Add ability to merge Document.Body.Data values

JSONAPI.playground/Pages/Usage.xcplaygroundpage/Contents.swift

@@ -19,7 +19,14 @@ let singleDogData = try! JSONEncoder().encode(singleDogDocument)
 
 // MARK: - Parse a request or response body with one Dog in it
 let dogResponse = try! JSONDecoder().decode(SingleDogDocument.self, from: singleDogData)
-let dogFromData = dogResponse.body.primaryData?.value
+let dogFromData = dogResponse.body.primaryResource?.value
+let dogOwner: Person.Identifier? = dogFromData.flatMap { $0 ~> \.owner }
+
+// MARKL - Parse a request or response body with one Dog in it using an alternative model
+typealias AltSingleDogDocument = JSONAPI.Document<SingleResourceBody<AlternativeDog>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>
+let altDogResponse = try! JSONDecoder().decode(AltSingleDogDocument.self, from: singleDogData)
+let altDogFromData = altDogResponse.body.primaryResource?.value
+let altDogHuman: Person.Identifier? = altDogFromData.flatMap { $0 ~> \.human }
 
 // MARK: - Create a request or response with multiple people and dogs and houses included
 let personIds = [Person.Identifier(), Person.Identifier()]
@@ -36,7 +43,7 @@ let batchPeopleData = try! JSONEncoder().encode(batchPeopleDocument)
 // MARK: - Parse a request or response body with multiple people in it and dogs and houses included
 
 let peopleResponse = try! JSONDecoder().decode(BatchPeopleDocument.self, from: batchPeopleData)
-let peopleFromData = peopleResponse.body.primaryData?.values
+let peopleFromData = peopleResponse.body.primaryResource?.values
 let dogsFromData = peopleResponse.body.includes?[Dog.self]
 let housesFromData = peopleResponse.body.includes?[House.self]
 

JSONAPI.playground/Sources/Entities.swift

@@ -91,6 +91,34 @@ public enum DogDescription: EntityDescription {
 
 public typealias Dog = ExampleEntity<DogDescription>
 
+public enum AlternativeDogDescription: EntityDescription {
+
+	public static var type: String { return "dogs" }
+
+	public struct Attributes: JSONAPI.Attributes {
+		public let name: Attribute<String>
+
+		public init(name: Attribute<String>) {
+			self.name = name
+		}
+	}
+
+	public struct Relationships: JSONAPI.Relationships {
+		public let human: ToOne<Person?>
+
+		public init(human: ToOne<Person?>) {
+			self.human = human
+		}
+
+		// define custom key mapping:
+		enum CodingKeys: String, CodingKey {
+			case human = "owner"
+		}
+	}
+}
+
+public typealias AlternativeDog = ExampleEntity<AlternativeDogDescription>
+
 public extension Entity where Description == DogDescription, MetaType == NoMetadata, LinksType == NoLinks, EntityRawIdType == String {
 	public init(name: String, owner: Person?) throws {
 		self = try Dog(attributes: .init(name: .init(rawValue: name)), relationships: DogDescription.Relationships(owner: .init(entity: owner)), meta: .none, links: .none)

README.md

@@ -67,7 +67,7 @@ Note that Playground support for importing non-system Frameworks is still a bit
 ### JSONAPITestLib
 #### Entity Validator
 - [x] Disallow optional array in `Attribute` (should be empty array, not `null`).
-- [x] Only allow `TransformedAttribute` and its derivatives within `Attributes` struct.
+- [x] Only allow `TransformedAttribute` and its derivatives as stored properties within `Attributes` struct. Computed properties can still be any type because they do not get encoded or decoded.
 - [x] Only allow `ToManyRelationship` and `ToOneRelationship` within `Relationships` struct.
 
 ### Potential Improvements
@@ -227,6 +227,11 @@ typealias Attributes = NoAttributes
 let favoriteColor: String = person[\.favoriteColor]
 ```
 
+NOTE: Because of support for computed properties that are not wrapped in `Attribute`, `TransformedAttribute`, or `ValidatedAttribute`, the compiler cannot always infer the type of thing you want back when using subscript attribute access. The following code is ambiguous about whether it should return a `String` or an `Attribute<String>`:
+```
+let favoriteColor = person[\.favoriteColor]
+```
+
 #### `Transformer`
 
 Sometimes you need to use a type that does not encode or decode itself in the way you need to represent it as a serialized JSON object. For example, the Swift `Foundation` type `Date` can encode/decode itself to `Double` out of the box, but you might want to represent dates as ISO 8601 compliant `String`s instead. The Foundation library `JSONDecoder` has a setting to make this adjustment, but for the sake of an example, you could create a `Transformer`.
@@ -265,7 +270,7 @@ You can also creator `Validators` and `ValidatedAttribute`s. A `Validator` is ju
 
 #### Computed `Attribute`
 
-You can add computed properties to your `EntityDescription.Attributes` struct if you would like to expose attributes that are not explicitly represented by the JSON. These computed properties should still have the type `Attribute` because that way you can take advantage of the quick access provided by `Entity`'s subscript operator. Here's an example of how you might take the `Person[\.name]` attribute from the example above and create a `fullName` computed property.
+You can add computed properties to your `EntityDescription.Attributes` struct if you would like to expose attributes that are not explicitly represented by the JSON. These computed properties do not have to be wrapped in `Attribute`, `ValidatedAttribute`, or `TransformedAttribute`. This allows computed attributes to be of types that are not `Codable`. Here's an example of how you might take the `Person[\.name]` attribute from the example above and create a `fullName` computed property.
 
 ```
 public var fullName: Attribute<String> {
@@ -273,6 +278,23 @@ public var fullName: Attribute<String> {
 }
 ```
 
+### Copying `Entities`
+`Entity` is a value type, so copying is its default behavior. There are two common mutations you might want to make when copying an `Entity`:
+1. Assigning a new `Identifier` to the copy of an identified `Entity`.
+2. Assigning a new `Identifier` to the copy of an unidentified `Entity`.
+
+The above can be accomplished with code like the following:
+
+```
+// use case 1
+let person1 = person.withNewIdentifier()
+
+// use case 2
+let newlyIdentifiedPerson1 = unidentifiedPerson.identified(byType: String.self)
+
+let newlyIdentifiedPerson2 = unidentifiedPerson.identified(by: "2232")
+```
+
 ### `JSONAPI.Document`
 
 The entirety of a JSON API request or response is encoded or decoded from- or to a `Document`. As an example, a JSON API response containing one `Person` and no included entities could be decoded as follows:
@@ -377,5 +399,75 @@ extension String: CreatableRawIdType {
 }
 ```
 
+### Custom Attribute or Relationship Key Mapping
+There is not anything special going on at the `JSONAPI.Attributes` and `JSONAPI.Relationships` levels, so you can easily provide custom key mappings by taking advantage of `Codable`'s `CodingKeys` pattern. Here are two models that will encode/decode equivalently but offer different naming in your codebase:
+```
+public enum EntityDescription1: JSONAPI.EntityDescription {
+	public static var type: String { return "entity" }
+
+	public struct Attributes: JSONAPI.Attributes {
+		public let coolProperty: Attribute<String>
+	}
+
+	public typealias Relationships = NoRelationships
+}
+
+public enum EntityDescription2: JSONAPI.EntityDescription {
+	public static var type: String { return "entity" }
+
+	public struct Attributes: JSONAPI.Attributes {
+		public let wholeOtherThing: Attribute<String>
+
+		enum CodingKeys: String, CodingKey {
+			case wholeOtherThing = "coolProperty"
+		}
+	}
+}
+```
+
+### Custom Attribute Encode/Decode
+You can safely provide your own encoding or decoding functions for your Attributes struct if you need to as long as you are careful that your encode operation correctly reverses your decode operation. Although this is generally not necessary, `AttributeType` provides a convenience method to make your decoding a bit less boilerplate ridden. This is what it looks like:
+```
+public enum EntityDescription1: JSONAPI.EntityDescription {
+	public static var type: String { return "entity" }
+
+	public struct Attributes: JSONAPI.Attributes {
+		public let property1: Attribute<String>
+		public let property2: Attribute<Int>
+		public let property3: Attribute<String>
+
+		public let weirdThing: Attribute<String>
+
+		enum CodingKeys: String, CodingKey {
+			case property1
+			case property2
+			case property3
+		}
+	}
+
+	public typealias Relationships = NoRelationships
+}
+
+extension EntityDescription1.Attributes {
+	public init(from decoder: Decoder) throws {
+		let container = try decoder.container(keyedBy: CodingKeys.self)
+
+		property1 = try .defaultDecoding(from: container, forKey: .property1)
+		property2 = try .defaultDecoding(from: container, forKey: .property2)
+		property3 = try .defaultDecoding(from: container, forKey: .property3)
+
+		weirdThing = .init(value: "hello world")
+	}
+
+	public func encode(to encoder: Encoder) throws {
+		var container = encoder.container(keyedBy: CodingKeys.self)
+
+		try container.encode(property1, forKey: .property1)
+		try container.encode(property2, forKey: .property2)
+		try container.encode(property3, forKey: .property3)
+	}
+}
+```
+
 # JSONAPITestLib
 The `JSONAPI` framework is packaged with a test library to help you test your `JSONAPI` integration. The test library is called `JSONAPITestLib`. It provides literal expressibility for `Attribute`, `ToOneRelationship`, and `Id` in many situations so that you can easily write test `Entity` values into your unit tests. It also provides a `check()` function for each `Entity` type that can be used to catch problems with your `JSONAPI` structures that are not caught by Swift's type system. You can see the `JSONAPITestLib` in action in the Playground included with the `JSONAPI` repository.

Sources/JSONAPI/Document/Document.swift

@@ -66,8 +66,13 @@ public struct Document<PrimaryResourceBody: JSONAPI.ResourceBody, MetaType: JSON
 			guard case let .errors(errors, meta: _, links: _) = self else { return nil }
 			return errors
 		}
+
+		public var data: Data? {
+			guard case let .data(data) = self else { return nil }
+			return data
+		}
 		
-		public var primaryData: PrimaryResourceBody? {
+		public var primaryResource: PrimaryResourceBody? {
 			guard case let .data(data) = self else { return nil }
 			return data.primary
 		}
@@ -184,6 +189,26 @@ extension Document where IncludeType == NoIncludes, MetaType == NoMetadata, Link
 }
 */
 
+extension Document.Body.Data where PrimaryResourceBody: AppendableResourceBody {
+	public func merging(_ other: Document.Body.Data,
+						combiningMetaWith metaMerge: (MetaType, MetaType) -> MetaType,
+						combiningLinksWith linksMerge: (LinksType, LinksType) -> LinksType) -> Document.Body.Data {
+		return Document.Body.Data(primary: primary.appending(other.primary),
+								  includes: includes.appending(other.includes),
+								  meta: metaMerge(meta, other.meta),
+								  links: linksMerge(links, other.links))
+	}
+}
+
+extension Document.Body.Data where PrimaryResourceBody: AppendableResourceBody, MetaType == NoMetadata, LinksType == NoLinks {
+	public func merging(_ other: Document.Body.Data) -> Document.Body.Data {
+		return merging(other,
+					   combiningMetaWith: { _, _ in .none },
+					   combiningLinksWith: { _, _ in .none })
+	}
+}
+
+// MARK: - Codable
 extension Document {
 	private enum RootCodingKeys: String, CodingKey {
 		case data

Sources/JSONAPI/Document/Includes.swift

@@ -50,6 +50,16 @@ public struct Includes<I: Include>: Codable, Equatable {
 	}
 }
 
+extension Includes {
+	public func appending(_ other: Includes<I>) -> Includes {
+		return Includes(values: values + other.values)
+	}
+}
+
+public func +<I: Include>(_ left: Includes<I>, _ right: Includes<I>) -> Includes<I> {
+	return left.appending(right)
+}
+
 extension Includes: CustomStringConvertible {
 	public var description: String {
 		return "Includes(\(String(describing: values))"
@@ -123,3 +133,17 @@ extension Includes where I: _Poly7 {
 }
 
 // MARK: - 8 includes
+public typealias Include8 = Poly8
+extension Includes where I: _Poly8 {
+	public subscript(_ lookup: I.H.Type) -> [I.H] {
+		return values.compactMap { $0.h }
+	}
+}
+
+// MARK: - 9 includes
+public typealias Include9 = Poly9
+extension Includes where I: _Poly9 {
+	public subscript(_ lookup: I.I.Type) -> [I.I] {
+		return values.compactMap { $0.i }
+	}
+}

Sources/JSONAPI/Document/ResourceBody.swift

@@ -19,6 +19,14 @@ extension Optional: MaybePrimaryResource where Wrapped: PrimaryResource {}
 public protocol ResourceBody: Codable, Equatable {
 }
 
+public protocol AppendableResourceBody: ResourceBody {
+	func appending(_ other: Self) -> Self
+}
+
+public func +<R: AppendableResourceBody>(_ left: R, right: R) -> R {
+	return left.appending(right)
+}
+
 public struct SingleResourceBody<Entity: JSONAPI.MaybePrimaryResource>: ResourceBody {
 	public let value: Entity
 
@@ -27,12 +35,16 @@ public struct SingleResourceBody<Entity: JSONAPI.MaybePrimaryResource>: Resource
 	}
 }
 
-public struct ManyResourceBody<Entity: JSONAPI.PrimaryResource>: ResourceBody {
+public struct ManyResourceBody<Entity: JSONAPI.PrimaryResource>: AppendableResourceBody {
 	public let values: [Entity]
 
 	public init(entities: [Entity]) {
 		values = entities
 	}
+
+	public func appending(_ other: ManyResourceBody) -> ManyResourceBody {
+		return ManyResourceBody(entities: values + other.values)
+	}
 }
 
 /// Use NoResourceBody to indicate you expect a JSON API document to not

Sources/JSONAPI/Resource/Attribute.swift

@@ -11,7 +11,7 @@ public protocol AttributeType: Codable {
 // MARK: TransformedAttribute
 /// A TransformedAttribute takes a Codable type and attempts to turn it into another type.
 public struct TransformedAttribute<RawValue: Codable, Transformer: JSONAPI.Transformer>: AttributeType where Transformer.From == RawValue {
-	private let rawValue: RawValue
+	let rawValue: RawValue
 	
 	public let value: Transformer.To
 	
@@ -84,3 +84,11 @@ extension TransformedAttribute {
 		try container.encode(rawValue)
 	}
 }
+
+// MARK: Attribute decoding and encoding defaults
+
+extension AttributeType {
+	public static func defaultDecoding<Container: KeyedDecodingContainerProtocol>(from container: Container, forKey key: Container.Key) throws -> Self {
+		return try container.decode(Self.self, forKey: key)
+	}
+}

Sources/JSONAPI/Resource/Entity.swift

@@ -8,11 +8,11 @@
 /// A JSON API structure within an Entity that contains
 /// named properties of types `ToOneRelationship` and
 /// `ToManyRelationship`.
-public typealias Relationships = Codable & Equatable
+public protocol Relationships: Codable & Equatable {}
 
 /// A JSON API structure within an Entity that contains
 /// properties of any types that are JSON encodable.
-public typealias Attributes = Codable & Equatable
+public protocol Attributes: Codable & Equatable {}
 
 /// Can be used as `Relationships` Type for Entities that do not
 /// have any Relationships.
@@ -32,21 +32,25 @@ public protocol JSONTyped {
 	static var type: String { get }
 }
 
+/// An `EntityProxyDescription` is an `EntityDescription`
+/// without Codable conformance.
+public protocol EntityProxyDescription: JSONTyped {
+	associatedtype Attributes: Equatable
+	associatedtype Relationships: Equatable
+}
+
 /// An `EntityDescription` describes a JSON API
 /// Resource Object. The Resource Object
 /// itself is encoded and decoded as an
 /// `Entity`, which gets specialized on an
 /// `EntityDescription`.
-public protocol EntityDescription: JSONTyped {
-	associatedtype Attributes: JSONAPI.Attributes
-	associatedtype Relationships: JSONAPI.Relationships
-}
+public protocol EntityDescription: EntityProxyDescription where Attributes: JSONAPI.Attributes, Relationships: JSONAPI.Relationships {}
 
 /// EntityProxy is a protocol that can be used to create
 /// types that _act_ like Entities but cannot be encoded
 /// or decoded as Entities.
 public protocol EntityProxy: Equatable, JSONTyped {
-	associatedtype Description: EntityDescription
+	associatedtype Description: EntityProxyDescription
 	associatedtype EntityRawIdType: JSONAPI.MaybeRawId
 
 	typealias Id = JSONAPI.Id<EntityRawIdType, Self>
@@ -75,7 +79,9 @@ extension EntityProxy {
 /// EntityType is the protocol that Entity conforms to. This
 /// protocol lets other types accept any Entity as a generic
 /// specialization.
-public protocol EntityType: EntityProxy, PrimaryResource {
+public protocol EntityType: EntityProxy, PrimaryResource where Description: EntityDescription {
+	associatedtype Meta: JSONAPI.Meta
+	associatedtype Links: JSONAPI.Links
 }
 
 public protocol IdentifiableEntityType: EntityType, Relatable where EntityRawIdType: JSONAPI.RawIdType {}
@@ -85,6 +91,10 @@ public protocol IdentifiableEntityType: EntityType, Relatable where EntityRawIdT
 /// "Resource Object."
 /// See https://jsonapi.org/format/#document-resource-objects
 public struct Entity<Description: JSONAPI.EntityDescription, MetaType: JSONAPI.Meta, LinksType: JSONAPI.Links, EntityRawIdType: JSONAPI.MaybeRawId>: EntityType {
+
+	public typealias Meta = MetaType
+	public typealias Links = LinksType
+
 	/// The `Entity`'s Id. This can be of type `Unidentified` if
 	/// the entity is being created clientside and the
 	/// server is being asked to create a unique Id. Otherwise,
@@ -377,10 +387,15 @@ extension Entity where MetaType == NoMetadata, LinksType == NoLinks, EntityRawId
 public extension Entity where EntityRawIdType: JSONAPI.RawIdType {
 
 	/// An Entity.Pointer is a `ToOneRelationship` with no metadata or links.
-	/// This is just a convenient way to reference an Entity given that
+	/// This is just a convenient way to reference an Entity so that
 	/// other Entities' Relationships can be built up from it.
 	public typealias Pointer = ToOneRelationship<Entity, NoMetadata, NoLinks>
 
+	/// Entity.Pointers is a `ToManyRelationship` with no metadata or links.
+	/// This is just a convenient way to reference a bunch of Entities so
+	/// that other Entities' Relationships can be built up from them.
+	public typealias Pointers = ToManyRelationship<Entity, NoMetadata, NoLinks>
+
 	/// Get a pointer to this entity that can be used as a
 	/// relationship to another entity.
 	public var pointer: Pointer {
@@ -392,6 +407,27 @@ public extension Entity where EntityRawIdType: JSONAPI.RawIdType {
 	}
 }
 
+// MARK: Identifying Unidentified Entities
+public extension Entity where EntityRawIdType == Unidentified {
+	/// Create a new Entity from this one with a newly created
+	/// unique Id of the given type.
+	public func identified<RawIdType: CreatableRawIdType>(byType: RawIdType.Type) -> Entity<Description, MetaType, LinksType, RawIdType> {
+		return .init(attributes: attributes, relationships: relationships, meta: meta, links: links)
+	}
+
+	/// Create a new Entity from this one with the given Id.
+	public func identified<RawIdType: JSONAPI.RawIdType>(by id: RawIdType) -> Entity<Description, MetaType, LinksType, RawIdType> {
+		return .init(id: Entity<Description, MetaType, LinksType, RawIdType>.Identifier(rawValue: id), attributes: attributes, relationships: relationships, meta: meta, links: links)
+	}
+}
+
+public extension Entity where EntityRawIdType: CreatableRawIdType {
+	/// Create a copy of this Entity with a new unique Id.
+	public func withNewIdentifier() -> Entity {
+		return Entity(attributes: attributes, relationships: relationships, meta: meta, links: links)
+	}
+}
+
 // MARK: Attribute Access
 public extension EntityProxy {
 	/// Access the attribute at the given keypath. This just
@@ -520,9 +556,10 @@ public extension Entity {
 
 		let maybeUnidentified = Unidentified() as? EntityRawIdType
 		id = try maybeUnidentified.map { Entity.Id(rawValue: $0) } ?? container.decode(Entity.Id.self, forKey: .id)
-		
-		attributes = try (NoAttributes() as? Description.Attributes) ?? container.decode(Description.Attributes.self, forKey: .attributes)
-		
+
+		attributes = try (NoAttributes() as? Description.Attributes) ??
+			container.decode(Description.Attributes.self, forKey: .attributes)
+
 		relationships = try (NoRelationships() as? Description.Relationships) ?? container.decode(Description.Relationships.self, forKey: .relationships)
 
 		meta = try (NoMetadata() as? MetaType) ?? container.decode(MetaType.self, forKey: .meta)

Sources/JSONAPI/Resource/Poly.swift

@@ -799,3 +799,360 @@ extension Poly7: CustomStringConvertible {
 		return "Poly(\(str))"
 	}
 }
+
+// MARK: - 8 types
+public protocol _Poly8: _Poly7 {
+	associatedtype H: EntityType
+	var h: H? { get }
+
+	init(_ h: H)
+}
+
+public extension _Poly8 {
+	subscript(_ lookup: H.Type) -> H? {
+		return h
+	}
+}
+
+public enum Poly8<A: EntityType, B: EntityType, C: EntityType, D: EntityType, E: EntityType, F: EntityType, G: EntityType, H: EntityType>: _Poly8 {
+	case a(A)
+	case b(B)
+	case c(C)
+	case d(D)
+	case e(E)
+	case f(F)
+	case g(G)
+	case h(H)
+
+	public var a: A? {
+		guard case let .a(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ a: A) {
+		self = .a(a)
+	}
+
+	public var b: B? {
+		guard case let .b(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ b: B) {
+		self = .b(b)
+	}
+
+	public var c: C? {
+		guard case let .c(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ c: C) {
+		self = .c(c)
+	}
+
+	public var d: D? {
+		guard case let .d(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ d: D) {
+		self = .d(d)
+	}
+
+	public var e: E? {
+		guard case let .e(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ e: E) {
+		self = .e(e)
+	}
+
+	public var f: F? {
+		guard case let .f(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ f: F) {
+		self = .f(f)
+	}
+
+	public var g: G? {
+		guard case let .g(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ g: G) {
+		self = .g(g)
+	}
+
+	public var h: H? {
+		guard case let .h(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ h: H) {
+		self = .h(h)
+	}
+
+	public init(from decoder: Decoder) throws {
+		let container = try decoder.singleValueContainer()
+
+		let attempts = [
+			try decode(A.self, from: container).map { Poly8.a($0) },
+			try decode(B.self, from: container).map { Poly8.b($0) },
+			try decode(C.self, from: container).map { Poly8.c($0) },
+			try decode(D.self, from: container).map { Poly8.d($0) },
+			try decode(E.self, from: container).map { Poly8.e($0) },
+			try decode(F.self, from: container).map { Poly8.f($0) },
+			try decode(G.self, from: container).map { Poly8.g($0) },
+			try decode(H.self, from: container).map { Poly8.h($0) }]
+
+		let maybeVal: Poly8<A, B, C, D, E, F, G, H>? = attempts
+			.compactMap { $0.value }
+			.first
+
+		guard let val = maybeVal else {
+			throw EncodingError.invalidValue(Poly8<A, B, C, D, E, F, G, H>.self, .init(codingPath: decoder.codingPath,
+																					   debugDescription: "Failed to find an include of the expected type. Attempts: \(attempts.map { $0.error }.compactMap { $0 })"))
+		}
+
+		self = val
+	}
+
+	public func encode(to encoder: Encoder) throws {
+		var container = encoder.singleValueContainer()
+
+		switch self {
+		case .a(let a):
+			try container.encode(a)
+		case .b(let b):
+			try container.encode(b)
+		case .c(let c):
+			try container.encode(c)
+		case .d(let d):
+			try container.encode(d)
+		case .e(let e):
+			try container.encode(e)
+		case .f(let f):
+			try container.encode(f)
+		case .g(let g):
+			try container.encode(g)
+		case .h(let h):
+			try container.encode(h)
+		}
+	}
+}
+
+extension Poly8: CustomStringConvertible {
+	public var description: String {
+		let str: String
+		switch self {
+		case .a(let a):
+			str = String(describing: a)
+		case .b(let b):
+			str = String(describing: b)
+		case .c(let c):
+			str = String(describing: c)
+		case .d(let d):
+			str = String(describing: d)
+		case .e(let e):
+			str = String(describing: e)
+		case .f(let f):
+			str = String(describing: f)
+		case .g(let g):
+			str = String(describing: g)
+		case .h(let h):
+			str = String(describing: h)
+		}
+
+		return "Poly(\(str))"
+	}
+}
+
+// MARK: - 9 types
+public protocol _Poly9: _Poly8 {
+	associatedtype I: EntityType
+	var i: I? { get }
+
+	init(_ i: I)
+}
+
+public extension _Poly9 {
+	subscript(_ lookup: I.Type) -> I? {
+		return i
+	}
+}
+
+public enum Poly9<A: EntityType, B: EntityType, C: EntityType, D: EntityType, E: EntityType, F: EntityType, G: EntityType, H: EntityType, I: EntityType>: _Poly9 {
+	case a(A)
+	case b(B)
+	case c(C)
+	case d(D)
+	case e(E)
+	case f(F)
+	case g(G)
+	case h(H)
+	case i(I)
+
+	public var a: A? {
+		guard case let .a(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ a: A) {
+		self = .a(a)
+	}
+
+	public var b: B? {
+		guard case let .b(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ b: B) {
+		self = .b(b)
+	}
+
+	public var c: C? {
+		guard case let .c(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ c: C) {
+		self = .c(c)
+	}
+
+	public var d: D? {
+		guard case let .d(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ d: D) {
+		self = .d(d)
+	}
+
+	public var e: E? {
+		guard case let .e(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ e: E) {
+		self = .e(e)
+	}
+
+	public var f: F? {
+		guard case let .f(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ f: F) {
+		self = .f(f)
+	}
+
+	public var g: G? {
+		guard case let .g(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ g: G) {
+		self = .g(g)
+	}
+
+	public var h: H? {
+		guard case let .h(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ h: H) {
+		self = .h(h)
+	}
+
+	public var i: I? {
+		guard case let .i(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ i: I) {
+		self = .i(i)
+	}
+
+	public init(from decoder: Decoder) throws {
+		let container = try decoder.singleValueContainer()
+
+		let attempts = [
+			try decode(A.self, from: container).map { Poly9.a($0) },
+			try decode(B.self, from: container).map { Poly9.b($0) },
+			try decode(C.self, from: container).map { Poly9.c($0) },
+			try decode(D.self, from: container).map { Poly9.d($0) },
+			try decode(E.self, from: container).map { Poly9.e($0) },
+			try decode(F.self, from: container).map { Poly9.f($0) },
+			try decode(G.self, from: container).map { Poly9.g($0) },
+			try decode(H.self, from: container).map { Poly9.h($0) },
+			try decode(I.self, from: container).map { Poly9.i($0) }]
+
+		let maybeVal: Poly9<A, B, C, D, E, F, G, H, I>? = attempts
+			.compactMap { $0.value }
+			.first
+
+		guard let val = maybeVal else {
+			throw EncodingError.invalidValue(Poly9<A, B, C, D, E, F, G, H, I>.self, .init(codingPath: decoder.codingPath,
+																						  debugDescription: "Failed to find an include of the expected type. Attempts: \(attempts.map { $0.error }.compactMap { $0 })"))
+		}
+
+		self = val
+	}
+
+	public func encode(to encoder: Encoder) throws {
+		var container = encoder.singleValueContainer()
+
+		switch self {
+		case .a(let a):
+			try container.encode(a)
+		case .b(let b):
+			try container.encode(b)
+		case .c(let c):
+			try container.encode(c)
+		case .d(let d):
+			try container.encode(d)
+		case .e(let e):
+			try container.encode(e)
+		case .f(let f):
+			try container.encode(f)
+		case .g(let g):
+			try container.encode(g)
+		case .h(let h):
+			try container.encode(h)
+		case .i(let i):
+			try container.encode(i)
+		}
+	}
+}
+
+extension Poly9: CustomStringConvertible {
+	public var description: String {
+		let str: String
+		switch self {
+		case .a(let a):
+			str = String(describing: a)
+		case .b(let b):
+			str = String(describing: b)
+		case .c(let c):
+			str = String(describing: c)
+		case .d(let d):
+			str = String(describing: d)
+		case .e(let e):
+			str = String(describing: e)
+		case .f(let f):
+			str = String(describing: f)
+		case .g(let g):
+			str = String(describing: g)
+		case .h(let h):
+			str = String(describing: h)
+		case .i(let i):
+			str = String(describing: i)
+		}
+
+		return "Poly(\(str))"
+	}
+}

Tests/JSONAPITests/Attribute/AttributeTests.swift

@@ -30,6 +30,18 @@ class AttributeTests: XCTestCase {
 		XCTAssertNoThrow(try TransformedAttribute<String, TestTransformer>(transformedValue: 10))
 	}
 
+	func test_EncodedPrimitives() {
+		testEncodedPrimitive(attribute: Attribute<Int>(value: 10))
+		testEncodedPrimitive(attribute: Attribute<Bool>(value: false))
+		testEncodedPrimitive(attribute: Attribute<Double>(value: 10.2))
+
+		testEncodedPrimitive(attribute: try! TransformedAttribute<Int, IntToString>(rawValue: 10))
+		testEncodedPrimitive(attribute: try! TransformedAttribute<Int, IntToInt>(rawValue: 10))
+		testEncodedPrimitive(attribute: try! TransformedAttribute<Int, IntToDouble>(rawValue: 10))
+		testEncodedPrimitive(attribute: try! TransformedAttribute<String, TestTransformer>(rawValue: "10"))
+		testEncodedPrimitive(attribute: try! TransformedAttribute<String?, OptionalToString<String>>(rawValue: "10"))
+	}
+
 	func test_NullableIsNullIfNil() {
 		struct Wrapper: Codable {
 			let dummy: Attribute<String?>
@@ -68,4 +80,28 @@ extension AttributeTests {
 			return String(value)
 		}
 	}
+
+	enum IntToString: Transformer {
+		public static func transform(_ from: Int) -> String {
+			return String(from)
+		}
+	}
+
+	enum IntToInt: Transformer {
+		public static func transform(_ from: Int) -> Int {
+			return from + 100
+		}
+	}
+
+	enum IntToDouble: Transformer {
+		public static func transform(_ from: Int) -> Double {
+			return Double(from)
+		}
+	}
+
+	enum OptionalToString<T>: Transformer {
+		public static func transform(_ from: T?) -> String {
+			return String(describing: from)
+		}
+	}
 }

Tests/JSONAPITests/Custom Attributes Tests/CustomAttributesTests.swift

@@ -0,0 +1,107 @@
+//
+//  CustomAttributesTests.swift
+//  JSONAPITests
+//
+//  Created by Mathew Polzin on 12/27/18.
+//
+
+import XCTest
+@testable import JSONAPI
+import JSONAPITestLib
+
+class CustomAttributesTests: XCTestCase {
+	func test_customDecode() {
+		let entity = decoded(type: CustomAttributeEntity.self, data: customAttributeEntityData)
+
+		XCTAssertEqual(entity[\.firstName], "Cool")
+		XCTAssertEqual(entity[\.name], "Cool Name")
+		XCTAssertNoThrow(try CustomAttributeEntity.check(entity))
+	}
+
+	func test_customEncode() {
+		test_DecodeEncodeEquality(type: CustomAttributeEntity.self,
+								  data: customAttributeEntityData)
+	}
+
+	func test_customKeysDecode() {
+		let entity = decoded(type: CustomKeysEntity.self, data: customAttributeEntityData)
+
+		XCTAssertEqual(entity[\.firstNameSilly], "Cool")
+		XCTAssertEqual(entity[\.lastNameSilly], "Name")
+		XCTAssertNoThrow(try CustomKeysEntity.check(entity))
+	}
+
+	func test_customKeysEncode() {
+		test_DecodeEncodeEquality(type: CustomKeysEntity.self,
+								  data: customAttributeEntityData)
+	}
+}
+
+// MARK: - Test Types
+extension CustomAttributesTests {
+	enum CustomAttributeEntityDescription: EntityDescription {
+		public static var type: String { return "test1" }
+
+		public struct Attributes: JSONAPI.Attributes {
+			let firstName: Attribute<String>
+			public let name: Attribute<String>
+
+			private enum CodingKeys: String, CodingKey {
+				case firstName
+				case lastName
+			}
+		}
+
+		public typealias Relationships = NoRelationships
+	}
+
+	typealias CustomAttributeEntity = BasicEntity<CustomAttributeEntityDescription>
+
+	enum CustomKeysEntityDescription: EntityDescription {
+		public static var type: String { return "test1" }
+
+		public struct Attributes: JSONAPI.Attributes {
+			public let firstNameSilly: Attribute<String>
+			public let lastNameSilly: Attribute<String>
+
+			enum CodingKeys: String, CodingKey {
+				case firstNameSilly = "firstName"
+				case lastNameSilly = "lastName"
+			}
+		}
+
+		public typealias Relationships = NoRelationships
+	}
+
+	typealias CustomKeysEntity = BasicEntity<CustomKeysEntityDescription>
+}
+
+extension CustomAttributesTests.CustomAttributeEntityDescription.Attributes {
+	public init(from decoder: Decoder) throws {
+		let container = try decoder.container(keyedBy: CodingKeys.self)
+
+		firstName = try .defaultDecoding(from: container, forKey: .firstName)
+		let lastName = try container.decode(String.self, forKey: .lastName)
+
+		name = firstName.map { "\($0) \(lastName)" }
+	}
+
+	public func encode(to encoder: Encoder) throws {
+		var container = encoder.container(keyedBy: CodingKeys.self)
+		try container.encode(firstName, forKey: .firstName)
+		let lastName = String(name.value.split(separator: " ")[1])
+		try container.encode(lastName, forKey: .lastName)
+	}
+}
+
+// MARK: - Test Data
+private let customAttributeEntityData = """
+{
+	"type": "test1",
+	"id": "1",
+	"attributes": {
+		"firstName": "Cool",
+		"lastName": "Name"
+	}
+}
+""".data(using: .utf8)!

Tests/JSONAPITests/Document/DocumentTests.swift

@@ -16,9 +16,9 @@ class DocumentTests: XCTestCase {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
+		XCTAssertNotNil(document.body.primaryResource)
 		XCTAssertEqual(document.body.meta, NoMetadata())
-		XCTAssertNil(document.body.primaryData?.value)
+		XCTAssertNil(document.body.primaryResource?.value)
 		XCTAssertEqual(document.body.includes?.count, 0)
 		XCTAssertEqual(document.body.links, NoLinks())
 		XCTAssertEqual(document.apiDescription, .none)
@@ -35,9 +35,9 @@ class DocumentTests: XCTestCase {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
+		XCTAssertNotNil(document.body.primaryResource)
 		XCTAssertEqual(document.body.meta, NoMetadata())
-		XCTAssertNil(document.body.primaryData?.value)
+		XCTAssertNil(document.body.primaryResource?.value)
 		XCTAssertEqual(document.body.includes?.count, 0)
 		XCTAssertEqual(document.body.links, NoLinks())
 		XCTAssertEqual(document.apiDescription.version, "1.0")
@@ -73,7 +73,7 @@ extension DocumentTests {
 
 		XCTAssertTrue(document.body.isError)
 		XCTAssertEqual(document.body.meta, NoMetadata())
-		XCTAssertNil(document.body.primaryData)
+		XCTAssertNil(document.body.primaryResource)
 		XCTAssertNil(document.body.includes)
 
 		guard case let .errors(errors) = document.body else {
@@ -98,7 +98,7 @@ extension DocumentTests {
 
 		XCTAssertTrue(document.body.isError)
 		XCTAssertEqual(document.body.meta, NoMetadata())
-		XCTAssertNil(document.body.primaryData)
+		XCTAssertNil(document.body.primaryResource)
 		XCTAssertNil(document.body.includes)
 		XCTAssertEqual(document.apiDescription.version, "1.0")
 
@@ -123,7 +123,7 @@ extension DocumentTests {
 
 		XCTAssertTrue(document.body.isError)
 		XCTAssertNil(document.body.meta)
-		XCTAssertNil(document.body.primaryData)
+		XCTAssertNil(document.body.primaryResource)
 		XCTAssertNil(document.body.includes)
 
 		guard case let .errors(errors) = document.body else {
@@ -146,7 +146,7 @@ extension DocumentTests {
 
 		XCTAssertTrue(document.body.isError)
 		XCTAssertNil(document.body.meta)
-		XCTAssertNil(document.body.primaryData)
+		XCTAssertNil(document.body.primaryResource)
 		XCTAssertNil(document.body.includes)
 		XCTAssertEqual(document.apiDescription.version, "1.0")
 
@@ -171,7 +171,7 @@ extension DocumentTests {
 
 		XCTAssertTrue(document.body.isError)
 		XCTAssertEqual(document.body.meta, NoMetadata())
-		XCTAssertNil(document.body.primaryData)
+		XCTAssertNil(document.body.primaryResource)
 		XCTAssertNil(document.body.includes)
 
 		guard case let .errors(errors) = document.body else {
@@ -196,7 +196,7 @@ extension DocumentTests {
 
 		XCTAssertTrue(document.body.isError)
 		XCTAssertEqual(document.body.meta, NoMetadata())
-		XCTAssertNil(document.body.primaryData)
+		XCTAssertNil(document.body.primaryResource)
 		XCTAssertNil(document.body.includes)
 		XCTAssertEqual(document.apiDescription.version, "1.0")
 
@@ -222,7 +222,7 @@ extension DocumentTests {
 
 		XCTAssertTrue(document.body.isError)
 		XCTAssertEqual(document.body.meta, TestPageMetadata(total: 70, limit: 40, offset: 10))
-		XCTAssertNil(document.body.primaryData)
+		XCTAssertNil(document.body.primaryResource)
 		XCTAssertNil(document.body.includes)
 
 		guard case let .errors(errors) = document.body else {
@@ -246,7 +246,7 @@ extension DocumentTests {
 
 		XCTAssertTrue(document.body.isError)
 		XCTAssertEqual(document.body.meta, TestPageMetadata(total: 70, limit: 40, offset: 10))
-		XCTAssertNil(document.body.primaryData)
+		XCTAssertNil(document.body.primaryResource)
 		XCTAssertNil(document.body.includes)
 		XCTAssertEqual(document.apiDescription.version, "1.0")
 
@@ -271,7 +271,7 @@ extension DocumentTests {
 
 		XCTAssertTrue(document.body.isError)
 		XCTAssertEqual(document.body.meta, TestPageMetadata(total: 70, limit: 40, offset: 10))
-		XCTAssertNil(document.body.primaryData)
+		XCTAssertNil(document.body.primaryResource)
 		XCTAssertNil(document.body.includes)
 
 		guard case let .errors(errors) = document.body else {
@@ -299,7 +299,7 @@ extension DocumentTests {
 
 		XCTAssertTrue(document.body.isError)
 		XCTAssertEqual(document.body.meta, TestPageMetadata(total: 70, limit: 40, offset: 10))
-		XCTAssertNil(document.body.primaryData)
+		XCTAssertNil(document.body.primaryResource)
 		XCTAssertNil(document.body.includes)
 		XCTAssertEqual(document.apiDescription.version, "1.0")
 
@@ -327,7 +327,7 @@ extension DocumentTests {
 							   data: error_document_with_links)
 
 		XCTAssertTrue(document.body.isError)
-		XCTAssertNil(document.body.primaryData)
+		XCTAssertNil(document.body.primaryResource)
 		XCTAssertNil(document.body.includes)
 
 		guard case let .errors(errors) = document.body else {
@@ -353,7 +353,7 @@ extension DocumentTests {
 							   data: error_document_with_links_with_api_description)
 
 		XCTAssertTrue(document.body.isError)
-		XCTAssertNil(document.body.primaryData)
+		XCTAssertNil(document.body.primaryResource)
 		XCTAssertNil(document.body.includes)
 		XCTAssertEqual(document.apiDescription.version, "1.0")
 
@@ -380,7 +380,7 @@ extension DocumentTests {
 							   data: error_document_no_metadata)
 
 		XCTAssertTrue(document.body.isError)
-		XCTAssertNil(document.body.primaryData)
+		XCTAssertNil(document.body.primaryResource)
 		XCTAssertNil(document.body.includes)
 
 		guard case let .errors(errors) = document.body else {
@@ -403,7 +403,7 @@ extension DocumentTests {
 							   data: error_document_no_metadata_with_api_description)
 
 		XCTAssertTrue(document.body.isError)
-		XCTAssertNil(document.body.primaryData)
+		XCTAssertNil(document.body.primaryResource)
 		XCTAssertNil(document.body.includes)
 		XCTAssertEqual(document.apiDescription.version, "1.0")
 
@@ -523,8 +523,8 @@ extension DocumentTests {
 		
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value.id.rawValue, "1")
 		XCTAssertEqual(document.body.includes?.count, 0)
 		XCTAssertEqual(document.body.meta, NoMetadata())
 	}
@@ -540,8 +540,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value.id.rawValue, "1")
 		XCTAssertEqual(document.body.includes?.count, 0)
 		XCTAssertEqual(document.body.meta, NoMetadata())
 		XCTAssertEqual(document.apiDescription.version, "1.0")
@@ -558,8 +558,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value?.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value?.id.rawValue, "1")
 		XCTAssertEqual(document.body.includes?.count, 0)
 		XCTAssertEqual(document.body.meta, NoMetadata())
 	}
@@ -575,8 +575,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value?.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value?.id.rawValue, "1")
 		XCTAssertEqual(document.body.includes?.count, 0)
 		XCTAssertEqual(document.body.meta, NoMetadata())
 		XCTAssertEqual(document.apiDescription.version, "1.0")
@@ -593,8 +593,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value.id.rawValue, "1")
 		XCTAssertEqual(document.body.includes?.count, 0)
 		XCTAssertEqual(document.body.meta, TestPageMetadata(total: 70, limit: 40, offset: 10))
 	}
@@ -610,8 +610,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value.id.rawValue, "1")
 		XCTAssertEqual(document.body.includes?.count, 0)
 		XCTAssertEqual(document.body.meta, TestPageMetadata(total: 70, limit: 40, offset: 10))
 		XCTAssertEqual(document.apiDescription.version, "1.0")
@@ -628,8 +628,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value.id.rawValue, "1")
 		XCTAssertEqual(document.body.includes?.count, 0)
 		XCTAssertEqual(document.body.meta, NoMetadata())
 		XCTAssertEqual(document.body.links?.link.url, "https://website.com")
@@ -650,8 +650,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value.id.rawValue, "1")
 		XCTAssertEqual(document.body.includes?.count, 0)
 		XCTAssertEqual(document.body.meta, NoMetadata())
 		XCTAssertEqual(document.body.links?.link.url, "https://website.com")
@@ -673,8 +673,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value.id.rawValue, "1")
 		XCTAssertEqual(document.body.includes?.count, 0)
 		XCTAssertEqual(document.body.meta, TestPageMetadata(total: 70, limit: 40, offset: 10))
 		XCTAssertEqual(document.body.links?.link.url, "https://website.com")
@@ -695,8 +695,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value.id.rawValue, "1")
 		XCTAssertEqual(document.body.includes?.count, 0)
 		XCTAssertEqual(document.body.meta, TestPageMetadata(total: 70, limit: 40, offset: 10))
 		XCTAssertEqual(document.body.links?.link.url, "https://website.com")
@@ -726,8 +726,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value.id.rawValue, "1")
 		XCTAssertEqual(document.body.includes?.count, 1)
 		XCTAssertEqual(document.body.includes?[Author.self].count, 1)
 		XCTAssertEqual(document.body.includes?[Author.self][0].id.rawValue, "33")
@@ -744,8 +744,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value.id.rawValue, "1")
 		XCTAssertEqual(document.body.includes?.count, 1)
 		XCTAssertEqual(document.body.includes?[Author.self].count, 1)
 		XCTAssertEqual(document.body.includes?[Author.self][0].id.rawValue, "33")
@@ -763,8 +763,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value.id.rawValue, "1")
 		XCTAssertEqual(document.body.includes?.count, 1)
 		XCTAssertEqual(document.body.includes?[Author.self].count, 1)
 		XCTAssertEqual(document.body.includes?[Author.self][0].id.rawValue, "33")
@@ -782,8 +782,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value.id.rawValue, "1")
 		XCTAssertEqual(document.body.includes?.count, 1)
 		XCTAssertEqual(document.body.includes?[Author.self].count, 1)
 		XCTAssertEqual(document.body.includes?[Author.self][0].id.rawValue, "33")
@@ -802,8 +802,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value.id.rawValue, "1")
 		XCTAssertEqual(document.body.meta, TestPageMetadata(total: 70, limit: 40, offset: 10))
 		XCTAssertEqual(document.body.links?.link.url, "https://website.com")
 		XCTAssertEqual(document.body.links?.link.meta, NoMetadata())
@@ -825,8 +825,8 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.value.id.rawValue, "1")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.value.id.rawValue, "1")
 		XCTAssertEqual(document.body.meta, TestPageMetadata(total: 70, limit: 40, offset: 10))
 		XCTAssertEqual(document.body.links?.link.url, "https://website.com")
 		XCTAssertEqual(document.body.links?.link.meta, NoMetadata())
@@ -850,8 +850,8 @@ extension DocumentTests {
 		let article = Article(id: Id(rawValue: "1"), attributes: .none, relationships: .init(author: ToOneRelationship(id: Id(rawValue: "33"))), meta: .none, links: .none)
 		let document = decoded(type: Document<SingleResourceBody<Poly2<Article, Author>>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>.self, data: single_document_no_includes)
 
-		XCTAssertEqual(document.body.primaryData?.value[Article.self], article)
-		XCTAssertNil(document.body.primaryData?.value[Author.self])
+		XCTAssertEqual(document.body.primaryResource?.value[Article.self], article)
+		XCTAssertNil(document.body.primaryResource?.value[Author.self])
 	}
 
 	func test_singleDocument_PolyPrimaryResource_encode() {
@@ -862,8 +862,8 @@ extension DocumentTests {
 		let article = Article(id: Id(rawValue: "1"), attributes: .none, relationships: .init(author: ToOneRelationship(id: Id(rawValue: "33"))), meta: .none, links: .none)
 		let document = decoded(type: Document<SingleResourceBody<Poly2<Article, Author>>, NoMetadata, NoLinks, NoIncludes, TestAPIDescription, UnknownJSONAPIError>.self, data: single_document_no_includes_with_api_description)
 
-		XCTAssertEqual(document.body.primaryData?.value[Article.self], article)
-		XCTAssertNil(document.body.primaryData?.value[Author.self])
+		XCTAssertEqual(document.body.primaryResource?.value[Article.self], article)
+		XCTAssertNil(document.body.primaryResource?.value[Author.self])
 		XCTAssertEqual(document.apiDescription.version, "1.0")
 	}
 
@@ -880,11 +880,11 @@ extension DocumentTests {
 		
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.values.count, 3)
-		XCTAssertEqual(document.body.primaryData?.values[0].id.rawValue, "1")
-		XCTAssertEqual(document.body.primaryData?.values[1].id.rawValue, "2")
-		XCTAssertEqual(document.body.primaryData?.values[2].id.rawValue, "3")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.values.count, 3)
+		XCTAssertEqual(document.body.primaryResource?.values[0].id.rawValue, "1")
+		XCTAssertEqual(document.body.primaryResource?.values[1].id.rawValue, "2")
+		XCTAssertEqual(document.body.primaryResource?.values[2].id.rawValue, "3")
 		XCTAssertEqual(document.body.includes?.count, 0)
 	}
 
@@ -899,11 +899,11 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.values.count, 3)
-		XCTAssertEqual(document.body.primaryData?.values[0].id.rawValue, "1")
-		XCTAssertEqual(document.body.primaryData?.values[1].id.rawValue, "2")
-		XCTAssertEqual(document.body.primaryData?.values[2].id.rawValue, "3")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.values.count, 3)
+		XCTAssertEqual(document.body.primaryResource?.values[0].id.rawValue, "1")
+		XCTAssertEqual(document.body.primaryResource?.values[1].id.rawValue, "2")
+		XCTAssertEqual(document.body.primaryResource?.values[2].id.rawValue, "3")
 		XCTAssertEqual(document.body.includes?.count, 0)
 		XCTAssertEqual(document.apiDescription.version, "1.0")
 	}
@@ -919,11 +919,11 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.values.count, 3)
-		XCTAssertEqual(document.body.primaryData?.values[0].id.rawValue, "1")
-		XCTAssertEqual(document.body.primaryData?.values[1].id.rawValue, "2")
-		XCTAssertEqual(document.body.primaryData?.values[2].id.rawValue, "3")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.values.count, 3)
+		XCTAssertEqual(document.body.primaryResource?.values[0].id.rawValue, "1")
+		XCTAssertEqual(document.body.primaryResource?.values[1].id.rawValue, "2")
+		XCTAssertEqual(document.body.primaryResource?.values[2].id.rawValue, "3")
 		XCTAssertEqual(document.body.includes?.count, 3)
 		XCTAssertEqual(document.body.includes?[Author.self].count, 3)
 		XCTAssertEqual(document.body.includes?[Author.self][0].id.rawValue, "33")
@@ -942,11 +942,11 @@ extension DocumentTests {
 
 		XCTAssertFalse(document.body.isError)
 		XCTAssertNil(document.body.errors)
-		XCTAssertNotNil(document.body.primaryData)
-		XCTAssertEqual(document.body.primaryData?.values.count, 3)
-		XCTAssertEqual(document.body.primaryData?.values[0].id.rawValue, "1")
-		XCTAssertEqual(document.body.primaryData?.values[1].id.rawValue, "2")
-		XCTAssertEqual(document.body.primaryData?.values[2].id.rawValue, "3")
+		XCTAssertNotNil(document.body.primaryResource)
+		XCTAssertEqual(document.body.primaryResource?.values.count, 3)
+		XCTAssertEqual(document.body.primaryResource?.values[0].id.rawValue, "1")
+		XCTAssertEqual(document.body.primaryResource?.values[1].id.rawValue, "2")
+		XCTAssertEqual(document.body.primaryResource?.values[2].id.rawValue, "3")
 		XCTAssertEqual(document.body.includes?.count, 3)
 		XCTAssertEqual(document.body.includes?[Author.self].count, 3)
 		XCTAssertEqual(document.body.includes?[Author.self][0].id.rawValue, "33")
@@ -961,6 +961,55 @@ extension DocumentTests {
 	}
 }
 
+// MARK: - Merging
+extension DocumentTests {
+	public func test_MergeBodyDataBasic(){
+		let entity1 = Article(attributes: .none, relationships: .init(author: "2"), meta: .none, links: .none)
+		let entity2 = Article(attributes: .none, relationships: .init(author: "3"), meta: .none, links: .none)
+
+		let bodyData1 = Document<ManyResourceBody<Article>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>.Body.Data(primary: .init(entities: [entity1]),
+																																			  includes: .none,
+																																			  meta: .none,
+																																			  links: .none)
+		let bodyData2 = Document<ManyResourceBody<Article>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>.Body.Data(primary: .init(entities: [entity2]),
+																																			  includes: .none,
+																																			  meta: .none,
+																																			  links: .none)
+		let combined = bodyData1.merging(bodyData2)
+
+		XCTAssertEqual(combined.primary.values, bodyData1.primary.values + bodyData2.primary.values)
+	}
+
+	public func test_MergeBodyDataWithMergeFunctions() {
+		let article1 = Article(attributes: .none, relationships: .init(author: "2"), meta: .none, links: .none)
+		let author1 = Author(id: "2", attributes: .none, relationships: .none, meta: .none, links: .none)
+		let article2 = Article(attributes: .none, relationships: .init(author: "3"), meta: .none, links: .none)
+		let author2 = Author(id: "3", attributes: .none, relationships: .none, meta: .none, links: .none)
+
+		let bodyData1 = Document<ManyResourceBody<Article>, TestPageMetadata, NoLinks, Include1<Author>, NoAPIDescription, UnknownJSONAPIError>.Body.Data(primary: .init(entities: [article1]),
+																																						  includes: .init(values: [.init(author1)]),
+																																						  meta: .init(total: 50, limit: 5, offset: 5),
+																																						  links: .none)
+		let bodyData2 = Document<ManyResourceBody<Article>, TestPageMetadata, NoLinks, Include1<Author>, NoAPIDescription, UnknownJSONAPIError>.Body.Data(primary: .init(entities: [article2]),
+																																						  includes: .init(values: [.init(author2)]),
+																																						  meta: .init(total: 60, limit: 5, offset: 5),
+																																						  links: .none)
+
+		let combined = bodyData1.merging(bodyData2,
+										 combiningMetaWith: { (meta1, meta2) in
+											return .init(total: max(meta1.total, meta2.total), limit: max(meta1.limit, meta2.limit), offset: max(meta1.offset, meta2.offset))
+		},
+										 combiningLinksWith: { _, _ in .none })
+
+		XCTAssertEqual(combined.meta.total, bodyData2.meta.total)
+		XCTAssertEqual(combined.meta.limit, bodyData2.meta.limit)
+		XCTAssertEqual(combined.meta.offset, bodyData1.meta.offset)
+
+		XCTAssertEqual(combined.includes, bodyData1.includes + bodyData2.includes)
+		XCTAssertEqual(combined.primary, bodyData1.primary + bodyData2.primary)
+	}
+}
+
 // MARK: - Test Types
 extension DocumentTests {
 	enum AuthorType: EntityDescription {

Tests/JSONAPITests/Entity/EntityTests.swift

@@ -26,7 +26,10 @@ class EntityTests: XCTestCase {
 	}
 
 	func test_optional_relationship_operator_access() {
-		
+		let entity1 = TestEntity1(attributes: .none, relationships: .none, meta: .none, links: .none)
+		let entity = TestEntity9(attributes: .none, relationships: .init(one: entity1.pointer, nullableOne: .init(entity: entity1, meta: .none, links: .none), optionalOne: .init(entity: entity1, meta: .none, links: .none), optionalNullableOne: nil, optionalMany: .init(entities: [entity1, entity1], meta: .none, links: .none)), meta: .none, links: .none)
+
+		XCTAssertEqual(entity ~> \.optionalOne, entity1.id)
 	}
 	
 	func test_toMany_relationship_operator_access() {
@@ -39,7 +42,10 @@ class EntityTests: XCTestCase {
 	}
 
 	func test_optionalToMany_relationship_opeartor_access() {
+		let entity1 = TestEntity1(attributes: .none, relationships: .none, meta: .none, links: .none)
+		let entity = TestEntity9(attributes: .none, relationships: .init(one: entity1.pointer, nullableOne: .init(entity: entity1, meta: .none, links: .none), optionalOne: nil, optionalNullableOne: nil, optionalMany: .init(entities: [entity1, entity1], meta: .none, links: .none)), meta: .none, links: .none)
 
+		XCTAssertEqual(entity ~> \.optionalMany, [entity1.id, entity1.id])
 	}
 	
 	func test_relationshipIds() {
@@ -59,6 +65,12 @@ class EntityTests: XCTestCase {
 		XCTAssertEqual(pointer.links.link1.url, "ok")
 	}
 
+	func test_unidentifiedEntityAttributeAccess() {
+		let entity = UnidentifiedTestEntity(attributes: .init(me: "hello"), relationships: .none, meta: .none, links: .none)
+
+		XCTAssertEqual(entity[\.me], "hello")
+	}
+
 	func test_initialization() {
 		let entity1 = TestEntity1(id: .init(rawValue: "wow"), attributes: .none, relationships: .none, meta: .none, links: .none)
 		let entity2 = TestEntity2(id: .init(rawValue: "cool"), attributes: .none, relationships: .init(other: .init(entity: entity1)), meta: .none, links: .none)
@@ -73,6 +85,7 @@ class EntityTests: XCTestCase {
 		XCTAssertNoThrow(try TestEntity8(id: .init(rawValue: "8"), attributes: .init(string: .init(value: "hello"), int: .init(value: 10), stringFromInt: .init(rawValue: 20), plus: .init(rawValue: 30), doubleFromInt: .init(rawValue: 32), omitted: nil, nullToString: .init(rawValue: nil)), relationships: .none, meta: .none, links: .none))
 		let _ = TestEntity9(id: .init(rawValue: "9"), attributes: .none, relationships: .init(one: entity1.pointer, nullableOne: nil, optionalOne: nil, optionalNullableOne: nil, optionalMany: nil), meta: .none, links: .none)
 		let _ = TestEntity9(id: .init(rawValue: "9"), attributes: .none, relationships: .init(one: entity1.pointer, nullableOne: .init(entity: nil), optionalOne: nil, optionalNullableOne: nil, optionalMany: nil), meta: .none, links: .none)
+		let _ = TestEntity9(id: .init(rawValue: "9"), attributes: .none, relationships: .init(one: entity1.pointer, nullableOne: .init(id: nil), optionalOne: nil, optionalNullableOne: nil, optionalMany: nil), meta: .none, links: .none)
 		let _ = TestEntity9(id: .init(rawValue: "9"), attributes: .none, relationships: .init(one: entity1.pointer, nullableOne: .init(entity: entity1, meta: .none, links: .none), optionalOne: nil, optionalNullableOne: nil, optionalMany: nil), meta: .none, links: .none)
 		let _ = TestEntity9(id: .init(rawValue: "9"), attributes: .none, relationships: .init(one: entity1.pointer, nullableOne: nil, optionalOne: entity1.pointer, optionalNullableOne: nil, optionalMany: nil), meta: .none, links: .none)
 		let _ = TestEntity9(id: .init(rawValue: "9"), attributes: .none, relationships: .init(one: entity1.pointer, nullableOne: nil, optionalOne: nil, optionalNullableOne: .init(entity: entity1, meta: .none, links: .none), optionalMany: nil), meta: .none, links: .none)
@@ -88,6 +101,36 @@ class EntityTests: XCTestCase {
 	}
 }
 
+// MARK: - Identifying entity copies
+extension EntityTests {
+	func test_copyIdentifiedByType() {
+		let unidentifiedEntity = UnidentifiedTestEntity(attributes: .init(me: .init(value: "hello")), relationships: .none, meta: .none, links: .none)
+
+		let identifiedCopy = unidentifiedEntity.identified(byType: String.self)
+
+		XCTAssertEqual(unidentifiedEntity.attributes, identifiedCopy.attributes)
+		XCTAssertEqual(unidentifiedEntity.relationships, identifiedCopy.relationships)
+	}
+
+	func test_copyIdentifiedByValue() {
+		let unidentifiedEntity = UnidentifiedTestEntity(attributes: .init(me: .init(value: "hello")), relationships: .none, meta: .none, links: .none)
+
+		let identifiedCopy = unidentifiedEntity.identified(by: "hello")
+
+		XCTAssertEqual(unidentifiedEntity.attributes, identifiedCopy.attributes)
+		XCTAssertEqual(unidentifiedEntity.relationships, identifiedCopy.relationships)
+		XCTAssertEqual(identifiedCopy.id, "hello")
+	}
+
+	func test_copyWithNewId() {
+		let identifiedEntity = TestEntity1(attributes: .none, relationships: .none, meta: .none, links: .none)
+
+		let identifiedCopy = identifiedEntity.withNewIdentifier()
+
+		XCTAssertNotEqual(identifiedEntity.id, identifiedCopy.id)
+	}
+}
+
 // MARK: - Encode/Decode
 extension EntityTests {
 
@@ -98,6 +141,8 @@ extension EntityTests {
 		XCTAssert(type(of: entity.relationships) == NoRelationships.self)
 		XCTAssert(type(of: entity.attributes) == NoAttributes.self)
 		XCTAssertNoThrow(try TestEntity1.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_EntityNoRelationshipsNoAttributes_encode() {
@@ -113,6 +158,8 @@ extension EntityTests {
 
 		XCTAssertEqual(entity[\.floater], 123.321)
 		XCTAssertNoThrow(try TestEntity5.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_EntityNoRelationshipsSomeAttributes_encode() {
@@ -128,6 +175,8 @@ extension EntityTests {
 		
 		XCTAssertEqual((entity ~> \.others).map { $0.rawValue }, ["364B3B69-4DF1-467F-B52E-B0C9E44F666E"])
 		XCTAssertNoThrow(try TestEntity3.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_EntitySomeRelationshipsNoAttributes_encode() {
@@ -143,6 +192,8 @@ extension EntityTests {
 		XCTAssertEqual(entity[\.number], 992299)
 		XCTAssertEqual((entity ~> \.other).rawValue, "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF")
 		XCTAssertNoThrow(try TestEntity4.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_EntitySomeRelationshipsSomeAttributes_encode() {
@@ -162,6 +213,8 @@ extension EntityTests {
 		XCTAssertNil(entity[\.maybeHere])
 		XCTAssertEqual(entity[\.maybeNull], "World")
 		XCTAssertNoThrow(try TestEntity6.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_entityOneOmittedAttribute_encode() {
@@ -177,6 +230,8 @@ extension EntityTests {
 		XCTAssertEqual(entity[\.maybeHere], "World")
 		XCTAssertNil(entity[\.maybeNull])
 		XCTAssertNoThrow(try TestEntity6.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_entityOneNullAttribute_encode() {
@@ -192,6 +247,8 @@ extension EntityTests {
 		XCTAssertEqual(entity[\.maybeHere], "World")
 		XCTAssertEqual(entity[\.maybeNull], "!")
 		XCTAssertNoThrow(try TestEntity6.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_entityAllAttribute_encode() {
@@ -208,7 +265,7 @@ extension EntityTests {
 		XCTAssertNil(entity[\.maybeNull])
 		XCTAssertNoThrow(try TestEntity6.check(entity))
 
-		print(encodable: entity)
+		testEncoded(entity: entity)
 	}
 
 	func test_entityOneNullAndOneOmittedAttribute_encode() {
@@ -229,7 +286,7 @@ extension EntityTests {
 		XCTAssertNil(entity[\.maybeHereMaybeNull])
 		XCTAssertNoThrow(try TestEntity7.check(entity))
 
-		print(encodable: entity)
+		testEncoded(entity: entity)
 	}
 
 	func test_NullOptionalNullableAttribute_encode() {
@@ -244,6 +301,8 @@ extension EntityTests {
 		XCTAssertEqual(entity[\.here], "Hello")
 		XCTAssertEqual(entity[\.maybeHereMaybeNull], "World")
 		XCTAssertNoThrow(try TestEntity7.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_NonNullOptionalNullableAttribute_encode() {
@@ -265,6 +324,8 @@ extension EntityTests {
 		XCTAssertEqual(entity[\.doubleFromInt], 22.0)
 		XCTAssertEqual(entity[\.nullToString], "nil")
 		XCTAssertNoThrow(try TestEntity8.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_IntToString_encode() {
@@ -299,6 +360,8 @@ extension EntityTests {
 		XCTAssertNil(entity ~> \.optionalOne)
 		XCTAssertEqual((entity ~> \.optionalNullableOne)?.rawValue, "1229")
 		XCTAssertNoThrow(try TestEntity9.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_nullableRelationshipNotNullOrOmitted_encode() {
@@ -314,6 +377,8 @@ extension EntityTests {
 		XCTAssertEqual((entity ~> \.one).rawValue, "4459")
 		XCTAssertNil(entity ~> \.optionalNullableOne)
 		XCTAssertNoThrow(try TestEntity9.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_nullableRelationshipNotNull_encode() {
@@ -329,6 +394,8 @@ extension EntityTests {
 		XCTAssertEqual((entity ~> \.one).rawValue, "4459")
 		XCTAssertNil(entity ~> \.optionalNullableOne)
 		XCTAssertNoThrow(try TestEntity9.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_optionalNullableRelationshipNulled_encode() {
@@ -344,6 +411,8 @@ extension EntityTests {
 		XCTAssertEqual((entity ~> \.one).rawValue, "4452")
 		XCTAssertNil(entity ~> \.optionalNullableOne)
 		XCTAssertNoThrow(try TestEntity9.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_nullableRelationshipIsNull_encode() {
@@ -360,6 +429,8 @@ extension EntityTests {
 		XCTAssertEqual((entity ~> \.optionalMany)?[0].rawValue, "332223")
 		XCTAssertNil(entity ~> \.optionalNullableOne)
 		XCTAssertNoThrow(try TestEntity9.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_optionalToManyIsNotOmitted_encode() {
@@ -377,6 +448,8 @@ extension EntityTests {
 
 		XCTAssertEqual((entity ~> \.selfRef).rawValue, "1")
 		XCTAssertNoThrow(try TestEntity10.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_RleationshipsOfSameType_encode() {
@@ -395,6 +468,8 @@ extension EntityTests {
 		XCTAssertNil(entity[\.me])
 		XCTAssertEqual(entity.id, .unidentified)
 		XCTAssertNoThrow(try UnidentifiedTestEntity.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_UnidentifiedEntity_encode() {
@@ -409,6 +484,8 @@ extension EntityTests {
 		XCTAssertEqual(entity[\.me], "unknown")
 		XCTAssertEqual(entity.id, .unidentified)
 		XCTAssertNoThrow(try UnidentifiedTestEntity.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_UnidentifiedEntityWithAttributes_encode() {
@@ -429,6 +506,8 @@ extension EntityTests {
 		XCTAssertEqual(entity.meta.x, "world")
 		XCTAssertEqual(entity.meta.y, 5)
 		XCTAssertNoThrow(try UnidentifiedTestEntityWithMeta.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_UnidentifiedEntityWithAttributesAndMeta_encode() {
@@ -444,6 +523,8 @@ extension EntityTests {
 		XCTAssertEqual(entity.id, .unidentified)
 		XCTAssertEqual(entity.links.link1, .init(url: "https://image.com/image.png"))
 		XCTAssertNoThrow(try UnidentifiedTestEntityWithLinks.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_UnidentifiedEntityWithAttributesAndLinks_encode() {
@@ -461,6 +542,8 @@ extension EntityTests {
 		XCTAssertEqual(entity.meta.y, 5)
 		XCTAssertEqual(entity.links.link1, .init(url: "https://image.com/image.png"))
 		XCTAssertNoThrow(try UnidentifiedTestEntityWithMetaAndLinks.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_UnidentifiedEntityWithAttributesAndMetaAndLinks_encode() {
@@ -478,6 +561,8 @@ extension EntityTests {
 		XCTAssertEqual(entity.meta.x, "world")
 		XCTAssertEqual(entity.meta.y, 5)
 		XCTAssertNoThrow(try TestEntity4WithMeta.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_EntitySomeRelationshipsSomeAttributesWithMeta_encode() {
@@ -494,6 +579,8 @@ extension EntityTests {
 		XCTAssertEqual((entity ~> \.other).rawValue, "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF")
 		XCTAssertEqual(entity.links.link1, .init(url: "https://image.com/image.png"))
 		XCTAssertNoThrow(try TestEntity4WithLinks.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_EntitySomeRelationshipsSomeAttributesWithLinks_encode() {
@@ -512,6 +599,8 @@ extension EntityTests {
 		XCTAssertEqual(entity.meta.y, 5)
 		XCTAssertEqual(entity.links.link1, .init(url: "https://image.com/image.png"))
 		XCTAssertNoThrow(try TestEntity4WithMetaAndLinks.check(entity))
+
+		testEncoded(entity: entity)
 	}
 
 	func test_EntitySomeRelationshipsSomeAttributesWithMetaAndLinks_encode() {

Tests/JSONAPITests/Includes/IncludeTests.swift

@@ -1,6 +1,6 @@
 
 import XCTest
-import JSONAPI
+@testable import JSONAPI
 
 class IncludedTests: XCTestCase {
 
@@ -139,6 +139,57 @@ class IncludedTests: XCTestCase {
 		test_DecodeEncodeEquality(type: Includes<Include7<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity5, TestEntity6, TestEntity7>>.self,
 								  data: seven_different_type_includes)
 	}
+
+	func test_EightDifferentIncludes() {
+		let includes = decoded(type: Includes<Include8<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity5, TestEntity6, TestEntity7, TestEntity8>>.self,
+							   data: eight_different_type_includes)
+
+		XCTAssertEqual(includes[TestEntity.self].count, 1)
+		XCTAssertEqual(includes[TestEntity2.self].count, 1)
+		XCTAssertEqual(includes[TestEntity3.self].count, 1)
+		XCTAssertEqual(includes[TestEntity4.self].count, 1)
+		XCTAssertEqual(includes[TestEntity5.self].count, 1)
+		XCTAssertEqual(includes[TestEntity6.self].count, 1)
+		XCTAssertEqual(includes[TestEntity7.self].count, 1)
+		XCTAssertEqual(includes[TestEntity8.self].count, 1)
+	}
+
+	func test_EightDifferentIncludes_encode() {
+		test_DecodeEncodeEquality(type: Includes<Include8<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity5, TestEntity6, TestEntity7, TestEntity8>>.self,
+								  data: eight_different_type_includes)
+	}
+
+	func test_NineDifferentIncludes() {
+		let includes = decoded(type: Includes<Include9<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity5, TestEntity6, TestEntity7, TestEntity8, TestEntity9>>.self,
+							   data: nine_different_type_includes)
+
+		XCTAssertEqual(includes[TestEntity.self].count, 1)
+		XCTAssertEqual(includes[TestEntity2.self].count, 1)
+		XCTAssertEqual(includes[TestEntity3.self].count, 1)
+		XCTAssertEqual(includes[TestEntity4.self].count, 1)
+		XCTAssertEqual(includes[TestEntity5.self].count, 1)
+		XCTAssertEqual(includes[TestEntity6.self].count, 1)
+		XCTAssertEqual(includes[TestEntity7.self].count, 1)
+		XCTAssertEqual(includes[TestEntity8.self].count, 1)
+		XCTAssertEqual(includes[TestEntity9.self].count, 1)
+	}
+
+	func test_NineDifferentIncludes_encode() {
+		test_DecodeEncodeEquality(type: Includes<Include9<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity5, TestEntity6, TestEntity7, TestEntity8, TestEntity9>>.self,
+								  data: nine_different_type_includes)
+	}
+}
+
+extension IncludedTests {
+	func test_appending() {
+		let include1 = Includes<Include2<TestEntity8, TestEntity9>>(values: [.init(TestEntity8(attributes: .none, relationships: .none, meta: .none, links: .none)), .init(TestEntity9(attributes: .none, relationships: .none, meta: .none, links: .none)), .init(TestEntity8(attributes: .none, relationships: .none, meta: .none, links: .none))])
+
+		let include2 = Includes<Include2<TestEntity8, TestEntity9>>(values: [.init(TestEntity8(attributes: .none, relationships: .none, meta: .none, links: .none)), .init(TestEntity9(attributes: .none, relationships: .none, meta: .none, links: .none)), .init(TestEntity8(attributes: .none, relationships: .none, meta: .none, links: .none))])
+
+		let combined = include1 + include2
+
+		XCTAssertEqual(combined.values, include1.values + include2.values)
+	}
 }
 
 // MARK: - Test types
@@ -232,4 +283,26 @@ extension IncludedTests {
 	}
 
 	typealias TestEntity7 = BasicEntity<TestEntityType7>
+
+	enum TestEntityType8: EntityDescription {
+
+		typealias Attributes = NoAttributes
+
+		public static var type: String { return "test_entity8" }
+
+		typealias Relationships = NoRelationships
+	}
+
+	typealias TestEntity8 = BasicEntity<TestEntityType8>
+
+	enum TestEntityType9: EntityDescription {
+
+		typealias Attributes = NoAttributes
+
+		public static var type: String { return "test_entity9" }
+
+		typealias Relationships = NoRelationships
+	}
+
+	typealias TestEntity9 = BasicEntity<TestEntityType9>
 }

Tests/JSONAPITests/Includes/stubs/IncludeStubs.swift

@@ -354,3 +354,161 @@ let seven_different_type_includes = """
 	}
 ]
 """.data(using: .utf8)!
+
+let eight_different_type_includes = """
+[
+	{
+		"type": "test_entity1",
+		"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF",
+		"attributes": {
+			"foo": "Hello",
+			"bar": 123
+		}
+	},
+	{
+		"type": "test_entity2",
+		"id": "90F03B69-4DF1-467F-B52E-B0C9E44FC333",
+		"attributes": {
+			"foo": "World",
+			"bar": 456
+		},
+		"relationships": {
+			"entity1": {
+				"data": {
+					"type": "test_entity1",
+					"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+				}
+			}
+		}
+	},
+	{
+		"type": "test_entity3",
+		"id": "11223B69-4DF1-467F-B52E-B0C9E44FC443",
+		"relationships": {
+			"entity1": {
+				"data": {
+					"type": "test_entity1",
+					"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+				}
+			},
+			"entity2": {
+				"data": [
+					{
+						"type": "test_entity2",
+						"id": "90F03B69-4DF1-467F-B52E-B0C9E44FC333"
+					}
+				]
+			}
+		}
+	},
+	{
+		"type": "test_entity6",
+		"id": "11113B69-4DF1-467F-B52E-B0C9E44FC444",
+		"relationships": {
+			"entity4": {
+				"data": {
+					"type": "test_entity4",
+					"id": "364B3B69-4DF1-467F-B52E-B0C9E44F666E"
+				}
+			}
+		}
+	},
+	{
+		"type": "test_entity5",
+		"id": "A24B3B69-4DF1-467F-B52E-B0C9E44F436A"
+	},
+	{
+		"type": "test_entity4",
+		"id": "364B3B69-4DF1-467F-B52E-B0C9E44F666E"
+	},
+	{
+		"type": "test_entity7",
+		"id": "364B3B69-4DF1-222F-B52E-B0C9E44F666E"
+	},
+	{
+		"type": "test_entity8",
+		"id": "364B3B69-4DF1-222F-B52E-B0C9E44F266F"
+	}
+]
+""".data(using: .utf8)!
+
+let nine_different_type_includes = """
+[
+	{
+		"type": "test_entity1",
+		"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF",
+		"attributes": {
+			"foo": "Hello",
+			"bar": 123
+		}
+	},
+	{
+		"type": "test_entity2",
+		"id": "90F03B69-4DF1-467F-B52E-B0C9E44FC333",
+		"attributes": {
+			"foo": "World",
+			"bar": 456
+		},
+		"relationships": {
+			"entity1": {
+				"data": {
+					"type": "test_entity1",
+					"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+				}
+			}
+		}
+	},
+	{
+		"type": "test_entity3",
+		"id": "11223B69-4DF1-467F-B52E-B0C9E44FC443",
+		"relationships": {
+			"entity1": {
+				"data": {
+					"type": "test_entity1",
+					"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+				}
+			},
+			"entity2": {
+				"data": [
+					{
+						"type": "test_entity2",
+						"id": "90F03B69-4DF1-467F-B52E-B0C9E44FC333"
+					}
+				]
+			}
+		}
+	},
+	{
+		"type": "test_entity6",
+		"id": "11113B69-4DF1-467F-B52E-B0C9E44FC444",
+		"relationships": {
+			"entity4": {
+				"data": {
+					"type": "test_entity4",
+					"id": "364B3B69-4DF1-467F-B52E-B0C9E44F666E"
+				}
+			}
+		}
+	},
+	{
+		"type": "test_entity5",
+		"id": "A24B3B69-4DF1-467F-B52E-B0C9E44F436A"
+	},
+	{
+		"type": "test_entity4",
+		"id": "364B3B69-4DF1-467F-B52E-B0C9E44F666E"
+	},
+	{
+		"type": "test_entity7",
+		"id": "364B3B69-4DF1-222F-B52E-B0C9E44F666E"
+	},
+	{
+		"type": "test_entity8",
+		"id": "364B3B69-4DF1-222F-B52E-B0C9E44F266F"
+	},
+	{
+		"type": "test_entity9",
+		"id": "364B3B69-4DF1-218F-B52E-B0C9E44F2661"
+	}
+]
+""".data(using: .utf8)!

Tests/JSONAPITests/JSONAPITestLib/EntityCheckTests.swift

@@ -61,7 +61,7 @@ extension EntityCheckTests {
 	enum EnumAttributesDescription: EntityDescription {
 		public static var type: String { return "hello" }
 
-		public enum Attributes: Codable, Equatable {
+		public enum Attributes: JSONAPI.Attributes {
 			case hello
 
 			public init(from decoder: Decoder) throws {
@@ -82,7 +82,7 @@ extension EntityCheckTests {
 
 		public typealias Attributes = NoAttributes
 
-		public enum Relationships: Codable, Equatable {
+		public enum Relationships: JSONAPI.Relationships {
 			case hello
 
 			public init(from decoder: Decoder) throws {

Tests/JSONAPITests/Poly/PolyProxyTests.swift

@@ -23,6 +23,7 @@ public class PolyProxyTests: XCTestCase {
 		XCTAssertEqual(polyUserA[\.name], "Ken Moore")
 		XCTAssertEqual(polyUserA.id, "1")
 		XCTAssertEqual(polyUserA.relationships, .none)
+		XCTAssertEqual(polyUserA[\.x], .init(x: "y"))
 	}
 
 	func test_UserAAndBEncodeEquality() {
@@ -57,6 +58,7 @@ public class PolyProxyTests: XCTestCase {
 		XCTAssertEqual(polyUserB[\.name], "Ken Less")
 		XCTAssertEqual(polyUserB.id, "2")
 		XCTAssertEqual(polyUserB.relationships, .none)
+		XCTAssertEqual(polyUserB[\.x], .init(x: "y"))
 	}
 }
 
@@ -111,9 +113,9 @@ extension Poly2: EntityProxy, JSONTyped where A == PolyProxyTests.UserA, B == Po
 	public var attributes: SharedUserDescription.Attributes {
 		switch self {
 		case .a(let a):
-			return .init(name: .init(value: "\(a[\.firstName]) \(a[\.lastName])"))
+			return .init(name: .init(value: "\(a[\.firstName]) \(a[\.lastName])"), x: .init(x: "y"))
 		case .b(let b):
-			return .init(name: .init(value: b[\.name].joined(separator: " ")))
+			return .init(name: .init(value: b[\.name].joined(separator: " ")), x: .init(x: "y"))
 		}
 	}
 
@@ -121,14 +123,19 @@ extension Poly2: EntityProxy, JSONTyped where A == PolyProxyTests.UserA, B == Po
 		return .none
 	}
 
-	public enum SharedUserDescription: EntityDescription {
+	public enum SharedUserDescription: EntityProxyDescription {
 		public static var type: String { return A.type }
 
-		public struct Attributes: JSONAPI.Attributes {
+		public struct Attributes: Equatable {
 			let name: Attribute<String>
+			let x: SomeRandomThingThatIsNotCodable
 		}
 
 		public typealias Relationships = NoRelationships
+
+		public struct SomeRandomThingThatIsNotCodable: Equatable {
+			let x: String
+		}
 	}
 
 	public typealias Description = SharedUserDescription

Tests/JSONAPITests/Poly/PolyTests.swift

@@ -230,6 +230,191 @@ class PolyTests: XCTestCase {
 		XCTAssertNil(poly7.e)
 		XCTAssertNil(poly7.f)
 	}
+
+	func test_init_Poly8() {
+		let entity = TestEntity5(attributes: .none, relationships: .none, meta: .none, links: .none)
+		let poly = Poly8<TestEntity5, TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity6, TestEntity7, TestEntity8>(entity)
+		XCTAssertEqual(poly.a, entity)
+		XCTAssertNil(poly.b)
+		XCTAssertNil(poly.c)
+		XCTAssertNil(poly.d)
+		XCTAssertNil(poly.e)
+		XCTAssertNil(poly.f)
+		XCTAssertNil(poly.g)
+		XCTAssertNil(poly.h)
+
+		let poly2 = Poly8<TestEntity, TestEntity5, TestEntity2, TestEntity3, TestEntity4, TestEntity6, TestEntity7, TestEntity8>(entity)
+		XCTAssertEqual(poly2.b, entity)
+		XCTAssertNil(poly2.a)
+		XCTAssertNil(poly2.c)
+		XCTAssertNil(poly2.d)
+		XCTAssertNil(poly2.e)
+		XCTAssertNil(poly2.f)
+		XCTAssertNil(poly2.g)
+		XCTAssertNil(poly2.h)
+
+		let poly3 = Poly8<TestEntity, TestEntity2, TestEntity5, TestEntity3, TestEntity4, TestEntity6, TestEntity7, TestEntity8>(entity)
+		XCTAssertEqual(poly3.c, entity)
+		XCTAssertNil(poly3.a)
+		XCTAssertNil(poly3.b)
+		XCTAssertNil(poly3.d)
+		XCTAssertNil(poly3.e)
+		XCTAssertNil(poly3.f)
+		XCTAssertNil(poly3.g)
+		XCTAssertNil(poly3.h)
+
+		let poly4 = Poly8<TestEntity, TestEntity2, TestEntity3, TestEntity5, TestEntity4, TestEntity6, TestEntity7, TestEntity8>(entity)
+		XCTAssertEqual(poly4.d, entity)
+		XCTAssertNil(poly4.a)
+		XCTAssertNil(poly4.b)
+		XCTAssertNil(poly4.c)
+		XCTAssertNil(poly4.e)
+		XCTAssertNil(poly4.f)
+		XCTAssertNil(poly4.g)
+		XCTAssertNil(poly4.h)
+
+		let poly5 = Poly8<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity5, TestEntity6, TestEntity7, TestEntity8>(entity)
+		XCTAssertEqual(poly5.e, entity)
+		XCTAssertNil(poly5.a)
+		XCTAssertNil(poly5.b)
+		XCTAssertNil(poly5.c)
+		XCTAssertNil(poly5.d)
+		XCTAssertNil(poly5.f)
+		XCTAssertNil(poly5.g)
+		XCTAssertNil(poly5.h)
+
+		let poly6 = Poly8<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity6, TestEntity5, TestEntity7, TestEntity8>(entity)
+		XCTAssertEqual(poly6.f, entity)
+		XCTAssertNil(poly6.a)
+		XCTAssertNil(poly6.b)
+		XCTAssertNil(poly6.c)
+		XCTAssertNil(poly6.d)
+		XCTAssertNil(poly6.e)
+		XCTAssertNil(poly6.g)
+		XCTAssertNil(poly6.h)
+
+		let poly7 = Poly8<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity6, TestEntity7, TestEntity5, TestEntity8>(entity)
+		XCTAssertEqual(poly7.g, entity)
+		XCTAssertNil(poly7.a)
+		XCTAssertNil(poly7.b)
+		XCTAssertNil(poly7.c)
+		XCTAssertNil(poly7.d)
+		XCTAssertNil(poly7.e)
+		XCTAssertNil(poly7.f)
+		XCTAssertNil(poly7.h)
+
+		let poly8 = Poly8<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity6, TestEntity7, TestEntity8, TestEntity5>(entity)
+		XCTAssertEqual(poly8.h, entity)
+		XCTAssertNil(poly8.a)
+		XCTAssertNil(poly8.b)
+		XCTAssertNil(poly8.c)
+		XCTAssertNil(poly8.d)
+		XCTAssertNil(poly8.e)
+		XCTAssertNil(poly8.f)
+		XCTAssertNil(poly8.g)
+	}
+
+	func test_init_Poly9() {
+		let entity = TestEntity5(attributes: .none, relationships: .none, meta: .none, links: .none)
+		let poly = Poly9<TestEntity5, TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity6, TestEntity7, TestEntity8, TestEntity9>(entity)
+		XCTAssertEqual(poly.a, entity)
+		XCTAssertNil(poly.b)
+		XCTAssertNil(poly.c)
+		XCTAssertNil(poly.d)
+		XCTAssertNil(poly.e)
+		XCTAssertNil(poly.f)
+		XCTAssertNil(poly.g)
+		XCTAssertNil(poly.h)
+		XCTAssertNil(poly.i)
+
+		let poly2 = Poly9<TestEntity, TestEntity5, TestEntity2, TestEntity3, TestEntity4, TestEntity6, TestEntity7, TestEntity8, TestEntity9>(entity)
+		XCTAssertEqual(poly2.b, entity)
+		XCTAssertNil(poly2.a)
+		XCTAssertNil(poly2.c)
+		XCTAssertNil(poly2.d)
+		XCTAssertNil(poly2.e)
+		XCTAssertNil(poly2.f)
+		XCTAssertNil(poly2.g)
+		XCTAssertNil(poly2.h)
+		XCTAssertNil(poly2.i)
+
+		let poly3 = Poly9<TestEntity, TestEntity2, TestEntity5, TestEntity3, TestEntity4, TestEntity6, TestEntity7, TestEntity8, TestEntity9>(entity)
+		XCTAssertEqual(poly3.c, entity)
+		XCTAssertNil(poly3.a)
+		XCTAssertNil(poly3.b)
+		XCTAssertNil(poly3.d)
+		XCTAssertNil(poly3.e)
+		XCTAssertNil(poly3.f)
+		XCTAssertNil(poly3.g)
+		XCTAssertNil(poly3.h)
+		XCTAssertNil(poly3.i)
+
+		let poly4 = Poly9<TestEntity, TestEntity2, TestEntity3, TestEntity5, TestEntity4, TestEntity6, TestEntity7, TestEntity8, TestEntity9>(entity)
+		XCTAssertEqual(poly4.d, entity)
+		XCTAssertNil(poly4.a)
+		XCTAssertNil(poly4.b)
+		XCTAssertNil(poly4.c)
+		XCTAssertNil(poly4.e)
+		XCTAssertNil(poly4.f)
+		XCTAssertNil(poly4.g)
+		XCTAssertNil(poly4.h)
+		XCTAssertNil(poly4.i)
+
+		let poly5 = Poly9<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity5, TestEntity6, TestEntity7, TestEntity8, TestEntity9>(entity)
+		XCTAssertEqual(poly5.e, entity)
+		XCTAssertNil(poly5.a)
+		XCTAssertNil(poly5.b)
+		XCTAssertNil(poly5.c)
+		XCTAssertNil(poly5.d)
+		XCTAssertNil(poly5.f)
+		XCTAssertNil(poly5.g)
+		XCTAssertNil(poly5.h)
+		XCTAssertNil(poly5.i)
+
+		let poly6 = Poly9<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity6, TestEntity5, TestEntity7, TestEntity8, TestEntity9>(entity)
+		XCTAssertEqual(poly6.f, entity)
+		XCTAssertNil(poly6.a)
+		XCTAssertNil(poly6.b)
+		XCTAssertNil(poly6.c)
+		XCTAssertNil(poly6.d)
+		XCTAssertNil(poly6.e)
+		XCTAssertNil(poly6.g)
+		XCTAssertNil(poly6.h)
+		XCTAssertNil(poly6.i)
+
+		let poly7 = Poly9<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity6, TestEntity7, TestEntity5, TestEntity8, TestEntity9>(entity)
+		XCTAssertEqual(poly7.g, entity)
+		XCTAssertNil(poly7.a)
+		XCTAssertNil(poly7.b)
+		XCTAssertNil(poly7.c)
+		XCTAssertNil(poly7.d)
+		XCTAssertNil(poly7.e)
+		XCTAssertNil(poly7.f)
+		XCTAssertNil(poly7.h)
+		XCTAssertNil(poly7.i)
+
+		let poly8 = Poly9<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity6, TestEntity7, TestEntity8, TestEntity5, TestEntity9>(entity)
+		XCTAssertEqual(poly8.h, entity)
+		XCTAssertNil(poly8.a)
+		XCTAssertNil(poly8.b)
+		XCTAssertNil(poly8.c)
+		XCTAssertNil(poly8.d)
+		XCTAssertNil(poly8.e)
+		XCTAssertNil(poly8.f)
+		XCTAssertNil(poly8.g)
+		XCTAssertNil(poly8.i)
+
+		let poly9 = Poly9<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity6, TestEntity7, TestEntity8, TestEntity9, TestEntity5>(entity)
+		XCTAssertEqual(poly9.i, entity)
+		XCTAssertNil(poly9.a)
+		XCTAssertNil(poly9.b)
+		XCTAssertNil(poly9.c)
+		XCTAssertNil(poly9.d)
+		XCTAssertNil(poly9.e)
+		XCTAssertNil(poly9.f)
+		XCTAssertNil(poly9.g)
+		XCTAssertNil(poly9.h)
+	}
 }
 
 // MARK: - subscript lookup
@@ -303,6 +488,35 @@ extension PolyTests {
 		XCTAssertNil(poly[TestEntity6.self])
 		XCTAssertEqual(entity, poly[TestEntity7.self])
 	}
+
+	func test_Poly8_lookup() {
+		let entity = decoded(type: TestEntity8.self, data: poly_entity8)
+		let poly = decoded(type: Poly8<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity5, TestEntity6, TestEntity7, TestEntity8>.self, data: poly_entity8)
+
+		XCTAssertNil(poly[TestEntity.self])
+		XCTAssertNil(poly[TestEntity2.self])
+		XCTAssertNil(poly[TestEntity3.self])
+		XCTAssertNil(poly[TestEntity4.self])
+		XCTAssertNil(poly[TestEntity5.self])
+		XCTAssertNil(poly[TestEntity6.self])
+		XCTAssertNil(poly[TestEntity7.self])
+		XCTAssertEqual(entity, poly[TestEntity8.self])
+	}
+
+	func test_Poly9_lookup() {
+		let entity = decoded(type: TestEntity9.self, data: poly_entity9)
+		let poly = decoded(type: Poly9<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity5, TestEntity6, TestEntity7, TestEntity8, TestEntity9>.self, data: poly_entity9)
+
+		XCTAssertNil(poly[TestEntity.self])
+		XCTAssertNil(poly[TestEntity2.self])
+		XCTAssertNil(poly[TestEntity3.self])
+		XCTAssertNil(poly[TestEntity4.self])
+		XCTAssertNil(poly[TestEntity5.self])
+		XCTAssertNil(poly[TestEntity6.self])
+		XCTAssertNil(poly[TestEntity7.self])
+		XCTAssertNil(poly[TestEntity8.self])
+		XCTAssertEqual(entity, poly[TestEntity9.self])
+	}
 }
 
 // MARK: - failures
@@ -342,6 +556,14 @@ extension PolyTests {
 	func test_Poly7_decode_throws_typeNotFound() {
 		XCTAssertThrowsError(try JSONDecoder().decode(Poly7<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity5, TestEntity6, TestEntity7>.self, from: poly_entity8))
 	}
+
+	func test_Poly8_decode_throws_typeNotFound() {
+		XCTAssertThrowsError(try JSONDecoder().decode(Poly8<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity5, TestEntity6, TestEntity7, TestEntity8>.self, from: poly_entity9))
+	}
+
+	func test_Poly9_decode_throws_typeNotFound() {
+		XCTAssertThrowsError(try JSONDecoder().decode(Poly9<TestEntity, TestEntity2, TestEntity3, TestEntity4, TestEntity5, TestEntity6, TestEntity7, TestEntity8, TestEntity9>.self, from: poly_entity10))
+	}
 }
 
 // MARK: - Test types
@@ -435,4 +657,26 @@ extension PolyTests {
 	}
 
 	typealias TestEntity7 = BasicEntity<TestEntityType7>
+
+	enum TestEntityType8: EntityDescription {
+
+		typealias Attributes = NoAttributes
+
+		public static var type: String { return "test_entity8" }
+
+		typealias Relationships = NoRelationships
+	}
+
+	typealias TestEntity8 = BasicEntity<TestEntityType8>
+
+	enum TestEntityType9: EntityDescription {
+
+		typealias Attributes = NoAttributes
+
+		public static var type: String { return "test_entity9" }
+
+		typealias Relationships = NoRelationships
+	}
+
+	typealias TestEntity9 = BasicEntity<TestEntityType9>
 }

Tests/JSONAPITests/Poly/stubs/PolyStubs.swift

@@ -100,3 +100,17 @@ let poly_entity8 = """
 	"id": "A24B3444-4DF1-467F-B52E-B0C9E44F436A"
 }
 """.data(using: .utf8)!
+
+let poly_entity9 = """
+{
+	"type": "test_entity9",
+	"id": "A24B3444-4DF1-467F-B52E-B0C2B44F436A"
+}
+""".data(using: .utf8)!
+
+let poly_entity10 = """
+{
+	"type": "test_entity10",
+	"id": "A24B3444-4DF1-467F-B52E-B0C9E12F436A"
+}
+""".data(using: .utf8)!

Tests/JSONAPITests/ResourceBody/ResourceBodyTests.swift

@@ -61,6 +61,31 @@ class ResourceBodyTests: XCTestCase {
 						   data: many_resource_body_empty)
 	}
 
+	func test_manyResourceBodyMerge() {
+		let body1 = ManyResourceBody(entities: [
+			Article(attributes: .init(title: "hello"),
+					relationships: .none,
+					meta: .none,
+					links: .none),
+			Article(attributes: .init(title: "world"),
+					relationships: .none,
+					meta: .none,
+					links: .none)
+			])
+
+		let body2 = ManyResourceBody(entities: [
+			Article(attributes: .init(title: "once more"),
+					relationships: .none,
+					meta: .none,
+					links: .none)
+			])
+
+		let combined = body1 + body2
+
+		XCTAssertEqual(combined.values.count, 3)
+		XCTAssertEqual(combined.values, body1.values + body2.values)
+	}
+
 	enum ArticleType: EntityDescription {
 		public static var type: String { return "articles" }