Update README and linuxmain

JSONAPI.playground/Sources/Entities.swift

@@ -23,8 +23,10 @@ extension String: CreatableRawIdType {
 	}
 }
 
-// MARK: - Entity typealias for convenience
-public typealias ExampleEntity<Description: EntityDescription> = Entity<Description, String>
+// MARK: - typealiases for convenience
+public typealias ExampleEntity<Description: EntityDescription> = Entity<Description, NoMetadata, NoLinks, String>
+public typealias ToOne<E: OptionalRelatable> = ToOneRelationship<E, NoMetadata, NoLinks>
+public typealias ToMany<E: Relatable> = ToManyRelationship<E, NoMetadata, NoLinks>
 
 // MARK: - A few resource objects (entities)
 public enum PersonDescription: EntityDescription {
@@ -46,11 +48,11 @@ public enum PersonDescription: EntityDescription {
 	}
 	
 	public struct Relationships: JSONAPI.Relationships {
-		public let friends: ToManyRelationship<Person>
-		public let dogs: ToManyRelationship<Dog>
-		public let home: ToOneRelationship<House>
+		public let friends: ToMany<Person>
+		public let dogs: ToMany<Dog>
+		public let home: ToOne<House>
 
-		public init(friends: ToManyRelationship<Person>, dogs: ToManyRelationship<Dog>, home: ToOneRelationship<House>) {
+		public init(friends: ToMany<Person>, dogs: ToMany<Dog>, home: ToOne<House>) {
 			self.friends = friends
 			self.dogs = dogs
 			self.home = home
@@ -60,7 +62,7 @@ public enum PersonDescription: EntityDescription {
 
 public typealias Person = ExampleEntity<PersonDescription>
 
-public extension Entity where Description == PersonDescription, EntityRawIdType == String {
+public extension Entity where Description == PersonDescription, MetaType == NoMetadata, LinksType == NoLinks, EntityRawIdType == String {
 	public init(id: Person.Id? = nil,name: [String], favoriteColor: String, friends: [Person], dogs: [Dog], home: House) throws {
 		self = try Person(id: id ?? Person.Id(), attributes: .init(name: .init(rawValue: name), favoriteColor: .init(rawValue: favoriteColor)), relationships: .init(friends: .init(entities: friends), dogs: .init(entities: dogs), home: .init(entity: home)))
 	}
@@ -79,9 +81,9 @@ public enum DogDescription: EntityDescription {
 	}
 
 	public struct Relationships: JSONAPI.Relationships {
-		public let owner: ToOneRelationship<Person?>
+		public let owner: ToOne<Person?>
 
-		public init(owner: ToOneRelationship<Person?>) {
+		public init(owner: ToOne<Person?>) {
 			self.owner = owner
 		}
 	}
@@ -89,7 +91,7 @@ public enum DogDescription: EntityDescription {
 
 public typealias Dog = ExampleEntity<DogDescription>
 
-public extension Entity where Description == DogDescription, EntityRawIdType == String {
+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)))
 	}

README.md

@@ -52,8 +52,8 @@ Note that Playground support for importing non-system Frameworks is still a bit
 
 #### Relationship Object
 - [x] `data`
-- [ ] `links`
-- [ ] `meta`
+- [x] `links`
+- [x] `meta`
 
 #### Links Object
 - [x] `href`
@@ -186,9 +186,11 @@ Note that I am assuming an unidentified person is a "new" person. I suspect that
 
 There are two types of `Relationships`: `ToOneRelationship` and `ToManyRelationship`. An `EntityDescription`'s `Relationships` type can contain any number of `Relationship` properties of either of these types. Do not store anything other than `Relationship` properties in the `Relationships` struct of an `EntityDescription`.
 
-To describe a relationship that may be omitted (i.e. the key is not even present in the JSON object), you make the entire `ToOneRelationship` or `ToManyRelationship` optional. However, this is not recommended because you can also represent optional relationships as nullable which means the key is always present. A `ToManyRelationship` can naturally represent the absence of related values with an empty array, so `ToManyRelationship` does not support nullability at all. A `ToOneRelationship` can be marked as nullable (i.e. the value might be `null` or it might be a resource identifier) like this:
+In addition to identifying entities by Id and type, `Relationships` can contain `Meta` or `Links` that follow the same rules as [`Meta`](#jsonapimeta) and [`Links`](#jsonapilinks) elsewhere in the JSON API Document.
+
+To describe a relationship that may be omitted (i.e. the key is not even present in the JSON object), you make the entire `ToOneRelationship` or `ToManyRelationship` optional. However, this is not recommended because you can also represent optional relationships as nullable which means the key is always present. A `ToManyRelationship` can naturally represent the absence of related values with an empty array, so `ToManyRelationship` does not support nullability at all. A `ToOneRelationship` can be marked as nullable (i.e. the value could be either `null` or a resource identifier) like this:
 ```
-let nullableRelative: ToOneRelationship<Person?>
+let nullableRelative: ToOneRelationship<Person?, NoMetadata, NoLinks>
 ```
 
 An entity that does not have relationships can be described by adding the following to an `EntityDescription`:

Sources/JSONAPI/Resource/Entity.swift

@@ -320,24 +320,46 @@ extension Entity where MetaType == NoMetadata {
 	}
 }
 
+extension Entity where MetaType == NoMetadata, EntityRawIdType: CreatableRawIdType {
+	public init(attributes: Description.Attributes, relationships: Description.Relationships, links: LinksType) {
+		self.init(attributes: attributes, relationships: relationships, meta: .none, links: links)
+	}
+}
+
 extension Entity where LinksType == NoLinks {
 	public init(id: Entity.Id, attributes: Description.Attributes, relationships: Description.Relationships, meta: MetaType) {
 		self.init(id: id, attributes: attributes, relationships: relationships, meta: meta, links: .none)
 	}
 }
 
+extension Entity where LinksType == NoLinks, EntityRawIdType: CreatableRawIdType {
+	public init(attributes: Description.Attributes, relationships: Description.Relationships, meta: MetaType) {
+		self.init(attributes: attributes, relationships: relationships, meta: meta, links: .none)
+	}
+}
+
 extension Entity where MetaType == NoMetadata, LinksType == NoLinks {
 	public init(id: Entity.Id, attributes: Description.Attributes, relationships: Description.Relationships) {
 		self.init(id: id, attributes: attributes, relationships: relationships, meta: .none, links: .none)
 	}
 }
 
+extension Entity where MetaType == NoMetadata, LinksType == NoLinks, EntityRawIdType: CreatableRawIdType {
+	public init(attributes: Description.Attributes, relationships: Description.Relationships) {
+		self.init(attributes: attributes, relationships: relationships, meta: .none, links: .none)
+	}
+}
+
 // MARK: Pointer for Relationships use.
 public extension Entity where EntityRawIdType: JSONAPI.RawIdType {
 	/// Get a pointer to this entity that can be used as a
 	/// relationship to another entity.
-	public var pointer: ToOneRelationship<Entity> {
-		return ToOneRelationship(entity: self)
+	public var pointer: ToOneRelationship<Entity, NoMetadata, NoLinks> {
+		return ToOneRelationship(entity: self, meta: .none, links: .none)
+	}
+
+	public func pointer<MType: JSONAPI.Meta, LType: JSONAPI.Links>(withMeta meta: MType, links: LType) -> ToOneRelationship<Entity, MType, LType> {
+		return ToOneRelationship(entity: self, meta: meta, links: links)
 	}
 }
 
@@ -370,14 +392,14 @@ public extension EntityProxy {
 	/// Access to an Id of a `ToOneRelationship`.
 	/// This allows you to write `entity ~> \.other` instead
 	/// of `entity.relationships.other.id`.
-	public static func ~><OtherEntity: OptionalRelatable>(entity: Self, path: KeyPath<Description.Relationships, ToOneRelationship<OtherEntity>>) -> OtherEntity.WrappedIdentifier {
+	public static func ~><OtherEntity: OptionalRelatable, MType: JSONAPI.Meta, LType: JSONAPI.Links>(entity: Self, path: KeyPath<Description.Relationships, ToOneRelationship<OtherEntity, MType, LType>>) -> OtherEntity.WrappedIdentifier {
 		return entity.relationships[keyPath: path].id
 	}
 
 	/// Access to all Ids of a `ToManyRelationship`.
 	/// This allows you to write `entity ~> \.others` instead
 	/// of `entity.relationships.others.ids`.
-	public static func ~><OtherEntity: Relatable>(entity: Self, path: KeyPath<Description.Relationships, ToManyRelationship<OtherEntity>>) -> [OtherEntity.Identifier] {
+	public static func ~><OtherEntity: Relatable, MType: JSONAPI.Meta, LType: JSONAPI.Links>(entity: Self, path: KeyPath<Description.Relationships, ToManyRelationship<OtherEntity, MType, LType>>) -> [OtherEntity.Identifier] {
 		return entity.relationships[keyPath: path].ids
 	}
 }

Sources/JSONAPI/Resource/Relationship.swift

@@ -5,30 +5,59 @@
 //  Created by Mathew Polzin on 8/31/18.
 //
 
-public protocol RelationshipType: Codable {}
+public protocol RelationshipType: Codable {
+	associatedtype LinksType
+	associatedtype MetaType
+
+	var links: LinksType { get }
+	var meta: MetaType { get }
+}
 
 /// An Entity relationship that can be encoded to or decoded from
 /// a JSON API "Resource Linkage."
 /// See https://jsonapi.org/format/#document-resource-object-linkage
 /// A convenient typealias might make your code much more legible: `One<EntityDescription>`
-public struct ToOneRelationship<Relatable: JSONAPI.OptionalRelatable>: RelationshipType, Equatable {
+public struct ToOneRelationship<Relatable: JSONAPI.OptionalRelatable, MetaType: JSONAPI.Meta, LinksType: JSONAPI.Links>: RelationshipType, Equatable {
 
 	public let id: Relatable.WrappedIdentifier
 
-	public init(id: Relatable.WrappedIdentifier) {
+	public let meta: MetaType
+	public let links: LinksType
+
+	public init(id: Relatable.WrappedIdentifier, meta: MetaType, links: LinksType) {
 		self.id = id
+		self.meta = meta
+		self.links = links
+	}
+}
+
+extension ToOneRelationship where MetaType == NoMetadata, LinksType == NoLinks {
+	public init(id: Relatable.WrappedIdentifier) {
+		self.init(id: id, meta: .none, links: .none)
 	}
 }
 
 extension ToOneRelationship where Relatable.WrappedIdentifier == Relatable.Identifier {
+	public init<E: EntityType>(entity: E, meta: MetaType, links: LinksType) where E.Description == Relatable.Description, E.Id == Relatable.Identifier {
+		self.init(id: entity.id, meta: meta, links: links)
+	}
+}
+
+extension ToOneRelationship where Relatable.WrappedIdentifier == Relatable.Identifier, MetaType == NoMetadata, LinksType == NoLinks {
 	public init<E: EntityType>(entity: E) where E.Description == Relatable.Description, E.Id == Relatable.Identifier {
-		id = entity.id
+		self.init(id: entity.id, meta: .none, links: .none)
 	}
 }
 
 extension ToOneRelationship where Relatable.WrappedIdentifier == Relatable.Identifier? {
+	public init<E: EntityType>(entity: E?, meta: MetaType, links: LinksType) where E.Description == Relatable.Description, E.Id == Relatable.Identifier {
+		self.init(id: entity?.id, meta: meta, links: links)
+	}
+}
+
+extension ToOneRelationship where Relatable.WrappedIdentifier == Relatable.Identifier?, MetaType == NoMetadata, LinksType == NoLinks {
 	public init<E: EntityType>(entity: E?) where E.Description == Relatable.Description, E.Id == Relatable.Identifier {
-		id = entity?.id
+		self.init(id: entity?.id, meta: .none, links: .none)
 	}
 }
 
@@ -36,30 +65,54 @@ extension ToOneRelationship where Relatable.WrappedIdentifier == Relatable.Ident
 /// a JSON API "Resource Linkage."
 /// See https://jsonapi.org/format/#document-resource-object-linkage
 /// A convenient typealias might make your code much more legible: `Many<EntityDescription>`
-public struct ToManyRelationship<Relatable: JSONAPI.Relatable>: RelationshipType, Equatable {
+public struct ToManyRelationship<Relatable: JSONAPI.Relatable, MetaType: JSONAPI.Meta, LinksType: JSONAPI.Links>: RelationshipType, Equatable {
 
 	public let ids: [Relatable.Identifier]
 
-	public init(ids: [Relatable.Identifier]) {
+	public let meta: MetaType
+	public let links: LinksType
+
+	public init(ids: [Relatable.Identifier], meta: MetaType, links: LinksType) {
 		self.ids = ids
+		self.meta = meta
+		self.links = links
 	}
 
-	public init<T: JSONAPI.Relatable>(relationships: [ToOneRelationship<T>]) where T.WrappedIdentifier == Relatable.Identifier {
+	public init<T: JSONAPI.Relatable>(relationships: [ToOneRelationship<T, NoMetadata, NoLinks>], meta: MetaType, links: LinksType) where T.WrappedIdentifier == Relatable.Identifier {
 		ids = relationships.map { $0.id }
+		self.meta = meta
+		self.links = links
 	}
 
-	private init() {
-		ids = []
+	public init<E: EntityType>(entities: [E], meta: MetaType, links: LinksType) where E.Description == Relatable.Description, E.Id == Relatable.Identifier {
+		self.init(ids: entities.map { $0.id }, meta: meta, links: links)
+	}
+
+	private init(meta: MetaType, links: LinksType) {
+		self.init(ids: [], meta: meta, links: links)
 	}
 	
-	public static var none: ToManyRelationship {
-		return .init()
+	public static func none(withMeta meta: MetaType, links: LinksType) -> ToManyRelationship {
+		return ToManyRelationship(meta: meta, links: links)
 	}
 }
 
-extension ToManyRelationship {
+extension ToManyRelationship where MetaType == NoMetadata, LinksType == NoLinks {
+
+	public init(ids: [Relatable.Identifier]) {
+		self.init(ids: ids, meta: .none, links: .none)
+	}
+
+	public init<T: JSONAPI.Relatable>(relationships: [ToOneRelationship<T, NoMetadata, NoLinks>]) where T.WrappedIdentifier == Relatable.Identifier {
+		self.init(relationships: relationships, meta: .none, links: .none)
+	}
+
+	public static var none: ToManyRelationship {
+		return .none(withMeta: .none, links: .none)
+	}
+
 	public init<E: EntityType>(entities: [E]) where E.Description == Relatable.Description, E.Id == Relatable.Identifier {
-		ids = entities.map { $0.id }
+		self.init(entities: entities, meta: .none, links: .none)
 	}
 }
 
@@ -85,6 +138,8 @@ extension Optional: OptionalRelatable where Wrapped: Relatable {
 // MARK: Codable
 private enum ResourceLinkageCodingKeys: String, CodingKey {
 	case data = "data"
+	case meta = "meta"
+	case links = "links"
 }
 private enum ResourceIdentifierCodingKeys: String, CodingKey {
 	case id = "id"
@@ -103,6 +158,18 @@ extension ToOneRelationship {
 	public init(from decoder: Decoder) throws {
 		let container = try decoder.container(keyedBy: ResourceLinkageCodingKeys.self)
 
+		if let noMeta = NoMetadata() as? MetaType {
+			meta = noMeta
+		} else {
+			meta = try container.decode(MetaType.self, forKey: .meta)
+		}
+
+		if let noLinks = NoLinks() as? LinksType {
+			links = noLinks
+		} else {
+			links = try container.decode(LinksType.self, forKey: .links)
+		}
+
 		// A little trickery follows. If the id is nil, the
 		// container.decode(Identifier.self) will fail even if Identifier
 		// is Optional. However, we can check if decoding nil
@@ -133,6 +200,14 @@ extension ToOneRelationship {
 			try container.encodeNil(forKey: .data)
 		}
 
+		if MetaType.self != NoMetadata.self {
+			try container.encode(meta, forKey: .meta)
+		}
+
+		if LinksType.self != NoLinks.self {
+			try container.encode(links, forKey: .links)
+		}
+
 		var identifier = container.nestedContainer(keyedBy: ResourceIdentifierCodingKeys.self, forKey: .data)
 		
 		try identifier.encode(id, forKey: .id)
@@ -143,7 +218,19 @@ extension ToOneRelationship {
 extension ToManyRelationship {
 	public init(from decoder: Decoder) throws {
 		let container = try decoder.container(keyedBy: ResourceLinkageCodingKeys.self)
-		
+
+		if let noMeta = NoMetadata() as? MetaType {
+			meta = noMeta
+		} else {
+			meta = try container.decode(MetaType.self, forKey: .meta)
+		}
+
+		if let noLinks = NoLinks() as? LinksType {
+			links = noLinks
+		} else {
+			links = try container.decode(LinksType.self, forKey: .links)
+		}
+
 		var identifiers = try container.nestedUnkeyedContainer(forKey: .data)
 		
 		var newIds = [Relatable.Identifier]()
@@ -163,6 +250,15 @@ extension ToManyRelationship {
 	
 	public func encode(to encoder: Encoder) throws {
 		var container = encoder.container(keyedBy: ResourceLinkageCodingKeys.self)
+
+		if MetaType.self != NoMetadata.self {
+			try container.encode(meta, forKey: .meta)
+		}
+
+		if LinksType.self != NoLinks.self {
+			try container.encode(links, forKey: .links)
+		}
+
 		var identifiers = container.nestedUnkeyedContainer(forKey: .data)
 		
 		for id in ids {

Sources/JSONAPITestLib/EntityCheck.swift

@@ -45,6 +45,10 @@ extension TransformedAttribute: AttributeTypeWithOptionalArray where RawValue: O
 private protocol OptionalRelationshipType {}
 extension Optional: OptionalRelationshipType where Wrapped: RelationshipType {}
 
+private protocol _RelationshipType {}
+extension ToOneRelationship: _RelationshipType {}
+extension ToManyRelationship: _RelationshipType {}
+
 public extension Entity {
 	public static func check(_ entity: Entity) throws {
 		var problems = [EntityCheckError]()
@@ -72,7 +76,7 @@ public extension Entity {
 		}
 
 		for relationship in relationshipsMirror.children {
-			if relationship.value as? RelationshipType == nil {
+			if relationship.value as? _RelationshipType == nil {
 				problems.append(.nonRelationship(named: relationship.label ?? "unnamed"))
 			}
 		}

Sources/JSONAPITestLib/Relationship+Literal.swift

@@ -7,14 +7,14 @@
 
 import JSONAPI
 
-extension ToOneRelationship: ExpressibleByNilLiteral where Relatable.WrappedIdentifier: ExpressibleByNilLiteral {
+extension ToOneRelationship: ExpressibleByNilLiteral where Relatable.WrappedIdentifier: ExpressibleByNilLiteral, MetaType == NoMetadata, LinksType == NoLinks {
 	public init(nilLiteral: ()) {
 
 		self.init(id: Relatable.WrappedIdentifier(nilLiteral: ()))
 	}
 }
 
-extension ToOneRelationship: ExpressibleByUnicodeScalarLiteral where Relatable.WrappedIdentifier: ExpressibleByUnicodeScalarLiteral {
+extension ToOneRelationship: ExpressibleByUnicodeScalarLiteral where Relatable.WrappedIdentifier: ExpressibleByUnicodeScalarLiteral, MetaType == NoMetadata, LinksType == NoLinks {
 	public typealias UnicodeScalarLiteralType =  Relatable.WrappedIdentifier.UnicodeScalarLiteralType
 
 	public init(unicodeScalarLiteral value: UnicodeScalarLiteralType) {
@@ -22,7 +22,7 @@ extension ToOneRelationship: ExpressibleByUnicodeScalarLiteral where Relatable.W
 	}
 }
 
-extension ToOneRelationship: ExpressibleByExtendedGraphemeClusterLiteral where Relatable.WrappedIdentifier: ExpressibleByExtendedGraphemeClusterLiteral {
+extension ToOneRelationship: ExpressibleByExtendedGraphemeClusterLiteral where Relatable.WrappedIdentifier: ExpressibleByExtendedGraphemeClusterLiteral, MetaType == NoMetadata, LinksType == NoLinks {
 	public typealias ExtendedGraphemeClusterLiteralType =  Relatable.WrappedIdentifier.ExtendedGraphemeClusterLiteralType
 
 	public init(extendedGraphemeClusterLiteral value: ExtendedGraphemeClusterLiteralType) {
@@ -30,7 +30,7 @@ extension ToOneRelationship: ExpressibleByExtendedGraphemeClusterLiteral where R
 	}
 }
 
-extension ToOneRelationship: ExpressibleByStringLiteral where Relatable.WrappedIdentifier: ExpressibleByStringLiteral {
+extension ToOneRelationship: ExpressibleByStringLiteral where Relatable.WrappedIdentifier: ExpressibleByStringLiteral, MetaType == NoMetadata, LinksType == NoLinks {
 	public typealias StringLiteralType = Relatable.WrappedIdentifier.StringLiteralType
 
 	public init(stringLiteral value: StringLiteralType) {
@@ -38,7 +38,7 @@ extension ToOneRelationship: ExpressibleByStringLiteral where Relatable.WrappedI
 	}
 }
 
-extension ToManyRelationship: ExpressibleByArrayLiteral {
+extension ToManyRelationship: ExpressibleByArrayLiteral where MetaType == NoMetadata, LinksType == NoLinks {
 	public typealias ArrayLiteralElement = Relatable.Identifier
 
 	public init(arrayLiteral elements: ArrayLiteralElement...) {

Tests/JSONAPITests/APIDescription/APIDescriptionTests.swift

@@ -10,6 +10,10 @@ import JSONAPI
 
 class APIDescriptionTests: XCTestCase {
 
+	func test_NoDescriptionString() {
+		XCTAssertEqual(String(describing: NoAPIDescription()), "No JSON:API Object")
+	}
+
 	func test_empty() {
 		let description = decoded(type: APIDescription<NoMetadata>.self, data: api_description_empty)
 

Tests/JSONAPITests/Computed Properties/ComputedPropertiesTests.swift

@@ -49,9 +49,9 @@ extension ComputedPropertiesTests {
 		}
 
 		public struct Relationships: JSONAPI.Relationships {
-			public let other: ToOneRelationship<TestType>
+			public let other: ToOneRelationship<TestType, NoMetadata, NoLinks>
 
-			public var computed: ToOneRelationship<TestType> {
+			public var computed: ToOneRelationship<TestType, NoMetadata, NoLinks> {
 				return other
 			}
 		}

Tests/JSONAPITests/Document/DocumentTests.swift

@@ -978,7 +978,7 @@ extension DocumentTests {
 		typealias Attributes = NoAttributes
 		
 		struct Relationships: JSONAPI.Relationships {
-			let author: ToOneRelationship<Author>
+			let author: ToOneRelationship<Author, NoMetadata, NoLinks>
 		}
 	}
 	

Tests/JSONAPITests/Entity/EntityTests.swift

@@ -41,16 +41,31 @@ class EntityTests: XCTestCase {
 		XCTAssertEqual(entity2.relationships.other.id, entity1.id)
 	}
 
+	func test_pointerWithMetaAndLinks() {
+		let entity = TestEntity4WithMetaAndLinks(attributes: .init(word: "hello", number: 10, array: []), relationships: .init(other: .init(id: "2")), meta: .init(x: "world", y: nil), links: .init(link1: .init(url: "ok")))
+
+		let pointer = entity.pointer(withMeta: TestEntityMeta(x: "world", y: nil), links: TestEntityLinks(link1: .init(url: "ok")))
+
+		XCTAssertEqual(pointer.id, entity.id)
+		XCTAssertEqual(pointer.meta.x, "world")
+		XCTAssertEqual(pointer.links.link1.url, "ok")
+	}
+
 	func test_initialization() {
 		let entity1 = TestEntity1(id: .init(rawValue: "wow"))
 		let entity2 = TestEntity2(id: .init(rawValue: "cool"), relationships: .init(other: .init(entity: entity1)))
+		let _ = TestEntity2(id: .init(rawValue: "cool"), attributes: .none, relationships: .init(other: .init(entity: entity1)))
+		let _ = TestEntity2(id: .init(rawValue: "cool"), relationships: .init(other: .init(entity: entity1)), meta: .none)
 		let _ = TestEntity3(id: .init(rawValue: "3"), relationships: .init(others: .init(ids: [.init(rawValue: "10"), .init(rawValue: "20"), entity1.id])))
+		let _ = TestEntity3(id: .init(rawValue: "3"), relationships: .init(others: .none))
 		let _ = TestEntity4(id: .init(rawValue: "4"), attributes: .init(word: .init(value: "hello"), number: .init(value: 10), array: .init(value: [10.2, 10.3])), relationships: .init(other: entity2.pointer))
 		let _ = TestEntity5(id: .init(rawValue: "5"), attributes: .init(floater: .init(value: 10.2)))
 		let _ = TestEntity6(id: .init(rawValue: "6"), attributes: .init(here: .init(value: "here"), maybeHere: nil, maybeNull: .init(value: nil)))
 		let _ = TestEntity7(id: .init(rawValue: "7"), attributes: .init(here: .init(value: "hello"), maybeHereMaybeNull: .init(value: "world")))
 		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))))
 		let _ = TestEntity9(id: .init(rawValue: "9"), relationships: .init(one: entity1.pointer, nullableOne: nil))
+		let _ = TestEntity9(id: .init(rawValue: "9"), relationships: .init(one: entity1.pointer, nullableOne: .init(entity: nil)))
+		let _ = TestEntity9(id: .init(rawValue: "9"), relationships: .init(one: entity1.pointer, nullableOne: .init(entity: entity1, meta: .none, links: .none)))
 		let e10id1 = TestEntity10.Identifier(rawValue: "hello")
 		let e10id2 = TestEntity10.Id(rawValue: "world")
 		let e10id3: TestEntity10.Id = "!"
@@ -459,7 +474,7 @@ extension EntityTests {
 		typealias Attributes = NoAttributes
 		
 		struct Relationships: JSONAPI.Relationships {
-			let other: ToOneRelationship<TestEntity1>
+			let other: ToOneRelationship<TestEntity1, NoMetadata, NoLinks>
 		}
 	}
 
@@ -471,7 +486,7 @@ extension EntityTests {
 		typealias Attributes = NoAttributes
 		
 		struct Relationships: JSONAPI.Relationships {
-			let others: ToManyRelationship<TestEntity1>
+			let others: ToManyRelationship<TestEntity1, NoMetadata, NoLinks>
 		}
 	}
 
@@ -481,7 +496,7 @@ extension EntityTests {
 		static var type: String { return "fourth_test_entities"}
 
 		struct Relationships: JSONAPI.Relationships {
-			let other: ToOneRelationship<TestEntity2>
+			let other: ToOneRelationship<TestEntity2, NoMetadata, NoLinks>
 		}
 
 		struct Attributes: JSONAPI.Attributes {
@@ -562,9 +577,9 @@ extension EntityTests {
 		typealias Attributes = NoAttributes
 
 		public struct Relationships: JSONAPI.Relationships {
-			let one: ToOneRelationship<TestEntity1>
+			let one: ToOneRelationship<TestEntity1, NoMetadata, NoLinks>
 
-			let nullableOne: ToOneRelationship<TestEntity1?>
+			let nullableOne: ToOneRelationship<TestEntity1?, NoMetadata, NoLinks>
 
 			// a nullable many is not allowed. it should
 			// just be an empty array.
@@ -584,8 +599,8 @@ extension EntityTests {
 		typealias Attributes = NoAttributes
 
 		public struct Relationships: JSONAPI.Relationships {
-			let selfRef: ToOneRelationship<TestEntity10>
-			let selfRefs: ToManyRelationship<TestEntity10>
+			let selfRef: ToOneRelationship<TestEntity10, NoMetadata, NoLinks>
+			let selfRefs: ToManyRelationship<TestEntity10, NoMetadata, NoLinks>
 		}
 	}
 

Tests/JSONAPITests/Includes/IncludeTests.swift

@@ -144,7 +144,7 @@ extension IncludedTests {
 		public static var type: String { return "test_entity2" }
 
 		public struct Relationships: JSONAPI.Relationships {
-			let entity1: ToOneRelationship<TestEntity>
+			let entity1: ToOneRelationship<TestEntity, NoMetadata, NoLinks>
 		}
 
 		public struct Attributes: JSONAPI.Attributes {
@@ -162,8 +162,8 @@ extension IncludedTests {
 		public static var type: String { return "test_entity3" }
 		
 		public struct Relationships: JSONAPI.Relationships {
-			let entity1: ToOneRelationship<TestEntity>
-			let entity2: ToManyRelationship<TestEntity2>
+			let entity1: ToOneRelationship<TestEntity, NoMetadata, NoLinks>
+			let entity2: ToManyRelationship<TestEntity2, NoMetadata, NoLinks>
 		}
 	}
 
@@ -198,7 +198,7 @@ extension IncludedTests {
 		public static var type: String { return "test_entity6" }
 
 		struct Relationships: JSONAPI.Relationships {
-			let entity4: ToOneRelationship<TestEntity4>
+			let entity4: ToOneRelationship<TestEntity4, NoMetadata, NoLinks>
 		}
 	}
 

Tests/JSONAPITests/JSONAPITestLib/EntityCheckTests.swift

@@ -115,7 +115,7 @@ extension EntityCheckTests {
 		public typealias Attributes = NoAttributes
 
 		public struct Relationships: JSONAPI.Relationships {
-			let x: ToOneRelationship<OkEntity>
+			let x: ToOneRelationship<OkEntity, NoMetadata, NoLinks>
 			let y: Id<String, OkEntity>
 		}
 	}

Tests/JSONAPITests/JSONAPITestLib/Relationship+LiteralTests.swift

@@ -12,16 +12,16 @@ import JSONAPITestLib
 class Relationship_LiteralTests: XCTestCase {
 
 	func test_NilLiteral() {
-		XCTAssertEqual(ToOneRelationship<TestEntity?>(id: nil), nil)
+		XCTAssertEqual(ToOneRelationship<TestEntity?, NoMetadata, NoLinks>(id: nil), nil)
 	}
 
 	func test_ArrayLiteral() {
-		XCTAssertEqual(ToManyRelationship<TestEntity>(ids: ["1", "2", "3"]), ["1", "2", "3"])
+		XCTAssertEqual(ToManyRelationship<TestEntity, NoMetadata, NoLinks>(ids: ["1", "2", "3"]), ["1", "2", "3"])
 	}
 
 	func test_StringLiteral() {
-		XCTAssertEqual(ToOneRelationship<TestEntity>(id: "123"), "123")
-		XCTAssertEqual(ToOneRelationship<TestEntity?>(id: "123"), "123")
+		XCTAssertEqual(ToOneRelationship<TestEntity, NoMetadata, NoLinks>(id: "123"), "123")
+		XCTAssertEqual(ToOneRelationship<TestEntity?, NoMetadata, NoLinks>(id: "123"), "123")
 	}
 }
 

Tests/JSONAPITests/Poly/PolyTests.swift

@@ -282,7 +282,7 @@ extension PolyTests {
 		public static var type: String { return "test_entity2" }
 
 		public struct Relationships: JSONAPI.Relationships {
-			let entity1: ToOneRelationship<TestEntity>
+			let entity1: ToOneRelationship<TestEntity, NoMetadata, NoLinks>
 		}
 
 		public struct Attributes: JSONAPI.Attributes {
@@ -300,8 +300,8 @@ extension PolyTests {
 		public static var type: String { return "test_entity3" }
 
 		public struct Relationships: JSONAPI.Relationships {
-			let entity1: ToOneRelationship<TestEntity>
-			let entity2: ToManyRelationship<TestEntity2>
+			let entity1: ToOneRelationship<TestEntity, NoMetadata, NoLinks>
+			let entity2: ToManyRelationship<TestEntity2, NoMetadata, NoLinks>
 		}
 	}
 
@@ -336,7 +336,7 @@ extension PolyTests {
 		public static var type: String { return "test_entity6" }
 
 		struct Relationships: JSONAPI.Relationships {
-			let entity4: ToOneRelationship<TestEntity4>
+			let entity4: ToOneRelationship<TestEntity4, NoMetadata, NoLinks>
 		}
 	}
 

Tests/JSONAPITests/Relationships/RelationshipTests.swift

@@ -15,7 +15,7 @@ class RelationshipTests: XCTestCase {
 		let entity2 = TestEntity1()
 		let entity3 = TestEntity1()
 		let entity4 = TestEntity1()
-		let relationship = ToManyRelationship<TestEntity1>(entities: [entity1, entity2, entity3, entity4])
+		let relationship = ToManyRelationship<TestEntity1, NoMetadata, NoLinks>(entities: [entity1, entity2, entity3, entity4])
 
 		XCTAssertEqual(relationship.ids.count, 4)
 		XCTAssertEqual(relationship.ids, [entity1, entity2, entity3, entity4].map { $0.id })
@@ -26,7 +26,7 @@ class RelationshipTests: XCTestCase {
 		let entity2 = TestEntity1()
 		let entity3 = TestEntity1()
 		let entity4 = TestEntity1()
-		let relationship = ToManyRelationship<TestEntity1>(relationships: [entity1.pointer, entity2.pointer, entity3.pointer, entity4.pointer])
+		let relationship = ToManyRelationship<TestEntity1, NoMetadata, NoLinks>(relationships: [entity1.pointer, entity2.pointer, entity3.pointer, entity4.pointer])
 
 		XCTAssertEqual(relationship.ids.count, 4)
 		XCTAssertEqual(relationship.ids, [entity1, entity2, entity3, entity4].map { $0.id })
@@ -36,38 +36,118 @@ class RelationshipTests: XCTestCase {
 // MARK: - Encode/Decode
 extension RelationshipTests {
 	func test_ToOneRelationship() {
-		let relationship = decoded(type: ToOneRelationship<TestEntity1>.self,
+		let relationship = decoded(type: ToOneRelationship<TestEntity1, NoMetadata, NoLinks>.self,
 								   data: to_one_relationship)
 
 		XCTAssertEqual(relationship.id.rawValue, "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF")
 	}
 
 	func test_ToOneRelationship_encode() {
-		test_DecodeEncodeEquality(type: ToOneRelationship<TestEntity1>.self,
+		test_DecodeEncodeEquality(type: ToOneRelationship<TestEntity1, NoMetadata, NoLinks>.self,
 								   data: to_one_relationship)
 	}
 
+	func test_ToOneRelationshipWithMeta() {
+		let relationship = decoded(type: ToOneWithMeta.self,
+								   data: to_one_relationship_with_meta)
+
+		XCTAssertEqual(relationship.id.rawValue, "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF")
+		XCTAssertEqual(relationship.meta.a, "hello")
+	}
+
+	func test_ToOneRelationshipWithMeta_encode() {
+		test_DecodeEncodeEquality(type: ToOneWithMeta.self,
+								  data: to_one_relationship_with_meta)
+	}
+
+	func test_ToOneRelationshipWithLinks() {
+		let relationship = decoded(type: ToOneWithLinks.self,
+								   data: to_one_relationship_with_links)
+
+		XCTAssertEqual(relationship.id.rawValue, "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF")
+		XCTAssertEqual(relationship.links.b, .init(url: "world"))
+	}
+
+	func test_ToOneRelationshipWithLinks_encode() {
+		test_DecodeEncodeEquality(type: ToOneWithLinks.self,
+								  data: to_one_relationship_with_links)
+	}
+
+	func test_ToOneRelationshipWithMetaAndLinks() {
+		let relationship = decoded(type: ToOneWithMetaAndLinks.self,
+								   data: to_one_relationship_with_meta_and_links)
+
+		XCTAssertEqual(relationship.id.rawValue, "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF")
+		XCTAssertEqual(relationship.meta.a, "hello")
+		XCTAssertEqual(relationship.links.b, .init(url: "world"))
+	}
+
+	func test_ToOneRelationshipWithMetaAndLinks_encode() {
+		test_DecodeEncodeEquality(type: ToOneWithMetaAndLinks.self,
+								  data: to_one_relationship_with_meta_and_links)
+	}
+
 	func test_ToManyRelationship() {
-		let relationship = decoded(type: ToManyRelationship<TestEntity1>.self,
+		let relationship = decoded(type: ToManyRelationship<TestEntity1, NoMetadata, NoLinks>.self,
 								   data: to_many_relationship)
 
 		XCTAssertEqual(relationship.ids.map { $0.rawValue }, ["2DF03B69-4B0A-467F-B52E-B0C9E44FCECF", "90F03B69-4DF1-467F-B52E-B0C9E44FC333", "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"])
 	}
 
 	func test_ToManyRelationship_encode() {
-		test_DecodeEncodeEquality(type: ToManyRelationship<TestEntity1>.self,
+		test_DecodeEncodeEquality(type: ToManyRelationship<TestEntity1, NoMetadata, NoLinks>.self,
 								   data: to_many_relationship)
 	}
+
+	func test_ToManyRelationshipWithMeta() {
+		let relationship = decoded(type: ToManyWithMeta.self,
+								   data: to_many_relationship_with_meta)
+
+		XCTAssertEqual(relationship.ids.map { $0.rawValue }, ["2DF03B69-4B0A-467F-B52E-B0C9E44FCECF", "90F03B69-4DF1-467F-B52E-B0C9E44FC333", "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"])
+		XCTAssertEqual(relationship.meta.a, "hello")
+	}
+
+	func test_ToManyRelationshipWithMeta_encode() {
+		test_DecodeEncodeEquality(type: ToManyWithMeta.self,
+								  data: to_many_relationship_with_meta)
+	}
+
+	func test_ToManyRelationshipWithLinks() {
+		let relationship = decoded(type: ToManyWithLinks.self,
+								   data: to_many_relationship_with_links)
+
+		XCTAssertEqual(relationship.ids.map { $0.rawValue }, ["2DF03B69-4B0A-467F-B52E-B0C9E44FCECF", "90F03B69-4DF1-467F-B52E-B0C9E44FC333", "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"])
+		XCTAssertEqual(relationship.links.b, .init(url: "world"))
+	}
+
+	func test_ToManyRelationshipWithLinks_encode() {
+		test_DecodeEncodeEquality(type: ToManyWithLinks.self,
+								  data: to_many_relationship_with_links)
+	}
+
+	func test_ToManyRelationshipWithMetaAndLinks() {
+		let relationship = decoded(type: ToManyWithMetaAndLinks.self,
+								   data: to_many_relationship_with_meta_and_links)
+
+		XCTAssertEqual(relationship.ids.map { $0.rawValue }, ["2DF03B69-4B0A-467F-B52E-B0C9E44FCECF", "90F03B69-4DF1-467F-B52E-B0C9E44FC333", "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"])
+		XCTAssertEqual(relationship.meta.a, "hello")
+		XCTAssertEqual(relationship.links.b, .init(url: "world"))
+	}
+
+	func test_ToManyRelationshipWithMetaAndLinks_encode() {
+		test_DecodeEncodeEquality(type: ToManyWithMetaAndLinks.self,
+								  data: to_many_relationship_with_meta_and_links)
+	}
 }
 
 // MARK: Failure tests
 extension RelationshipTests {
 	func test_ToManyTypeMismatch() {
-		XCTAssertThrowsError(try JSONDecoder().decode(ToManyRelationship<TestEntity1>.self, from: to_many_relationship_type_mismatch))
+		XCTAssertThrowsError(try JSONDecoder().decode(ToManyRelationship<TestEntity1, NoMetadata, NoLinks>.self, from: to_many_relationship_type_mismatch))
 	}
 
 	func test_ToOneTypeMismatch() {
-		XCTAssertThrowsError(try JSONDecoder().decode(ToOneRelationship<TestEntity1>.self, from: to_one_relationship_type_mismatch))
+		XCTAssertThrowsError(try JSONDecoder().decode(ToOneRelationship<TestEntity1, NoMetadata, NoLinks>.self, from: to_one_relationship_type_mismatch))
 	}
 }
 
@@ -82,4 +162,23 @@ extension RelationshipTests {
 	}
 
 	typealias TestEntity1 = BasicEntity<TestEntityType1>
+
+	typealias ToOneWithMeta = ToOneRelationship<TestEntity1, TestMeta, NoLinks>
+
+	typealias ToOneWithLinks = ToOneRelationship<TestEntity1, NoMetadata, TestLinks>
+	typealias ToOneWithMetaAndLinks = ToOneRelationship<TestEntity1, TestMeta, TestLinks>
+
+	typealias ToManyWithMeta = ToManyRelationship<TestEntity1, TestMeta, NoLinks>
+	typealias ToManyWithLinks = ToManyRelationship<TestEntity1, NoMetadata, TestLinks>
+	typealias ToManyWithMetaAndLinks = ToManyRelationship<TestEntity1, TestMeta, TestLinks>
+
+	struct TestMeta: JSONAPI.Meta {
+		let a: String
+	}
+
+	typealias TestLink = JSONAPI.Link<String, NoMetadata>
+
+	struct TestLinks: JSONAPI.Links {
+		let b: TestLink
+	}
 }

Tests/JSONAPITests/Relationships/stubs/RelationshipStubs.swift

@@ -23,6 +23,45 @@ let to_one_relationship_type_mismatch = """
 }
 """.data(using: .utf8)!
 
+let to_one_relationship_with_meta = """
+{
+	"data": {
+		"type": "test_entity1",
+		"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+	},
+	"meta": {
+		"a": "hello"
+	}
+}
+""".data(using: .utf8)!
+
+let to_one_relationship_with_links = """
+{
+	"data": {
+		"type": "test_entity1",
+		"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+	},
+	"links": {
+		"b": "world"
+	}
+}
+""".data(using: .utf8)!
+
+let to_one_relationship_with_meta_and_links = """
+{
+	"data": {
+		"type": "test_entity1",
+		"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+	},
+	"meta": {
+		"a": "hello"
+	},
+	"links": {
+		"b": "world"
+	}
+}
+""".data(using: .utf8)!
+
 let to_many_relationship = """
 {
 	"data": [
@@ -42,6 +81,75 @@ let to_many_relationship = """
 }
 """.data(using: .utf8)!
 
+let to_many_relationship_with_meta = """
+{
+	"data": [
+		{
+			"type": "test_entity1",
+			"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+		},
+		{
+			"type": "test_entity1",
+			"id": "90F03B69-4DF1-467F-B52E-B0C9E44FC333"
+		},
+		{
+			"type": "test_entity1",
+			"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+		}
+	],
+	"meta": {
+		"a": "hello"
+	}
+}
+""".data(using: .utf8)!
+
+let to_many_relationship_with_links = """
+{
+	"data": [
+		{
+			"type": "test_entity1",
+			"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+		},
+		{
+			"type": "test_entity1",
+			"id": "90F03B69-4DF1-467F-B52E-B0C9E44FC333"
+		},
+		{
+			"type": "test_entity1",
+			"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+		}
+	],
+	"links": {
+		"b": "world"
+	}
+}
+""".data(using: .utf8)!
+
+let to_many_relationship_with_meta_and_links = """
+{
+	"data": [
+		{
+			"type": "test_entity1",
+			"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+		},
+		{
+			"type": "test_entity1",
+			"id": "90F03B69-4DF1-467F-B52E-B0C9E44FC333"
+		},
+		{
+			"type": "test_entity1",
+			"id": "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"
+		}
+	],
+	"meta": {
+		"a": "hello"
+	},
+	"links": {
+		"b": "world"
+	}
+}
+""".data(using: .utf8)!
+
 let to_many_relationship_type_mismatch = """
 {
 	"data": [

Tests/JSONAPITests/ResourceBody/ResourceBodyTests.swift

@@ -10,6 +10,16 @@ import JSONAPI
 
 class ResourceBodyTests: XCTestCase {
 
+	func test_initializers() {
+		let articles = [
+			Article(attributes: .init(title: "hello")),
+			Article(attributes: .init(title: "world"))
+		]
+		let _ = SingleResourceBody(entity: articles[0])
+		let _ = ManyResourceBody(entities: articles)
+		let _: NoResourceBody = .none
+	}
+
 	func test_singleResourceBody() {
 		let body = decoded(type: SingleResourceBody<Article>.self,
 						   data: single_resource_body)

Tests/JSONAPITests/XCTestManifests.swift

@@ -4,6 +4,7 @@ extension APIDescriptionTests {
     static let __allTests = [
         ("test_empty", test_empty),
         ("test_failsMissingMeta", test_failsMissingMeta),
+        ("test_NoDescriptionString", test_NoDescriptionString),
         ("test_WithMeta", test_WithMeta),
         ("test_WithVersion", test_WithVersion),
         ("test_WithVersionAndMeta", test_WithVersionAndMeta),
@@ -195,6 +196,7 @@ extension EntityTests {
         ("test_nullableRelationshipNotNull_encode", test_nullableRelationshipNotNull_encode),
         ("test_NullOptionalNullableAttribute", test_NullOptionalNullableAttribute),
         ("test_NullOptionalNullableAttribute_encode", test_NullOptionalNullableAttribute_encode),
+        ("test_pointerWithMetaAndLinks", test_pointerWithMetaAndLinks),
         ("test_relationship_access", test_relationship_access),
         ("test_relationship_operator_access", test_relationship_operator_access),
         ("test_relationshipIds", test_relationshipIds),
@@ -300,9 +302,21 @@ extension RelationshipTests {
         ("test_initToManyWithRelationships", test_initToManyWithRelationships),
         ("test_ToManyRelationship", test_ToManyRelationship),
         ("test_ToManyRelationship_encode", test_ToManyRelationship_encode),
+        ("test_ToManyRelationshipWithLinks", test_ToManyRelationshipWithLinks),
+        ("test_ToManyRelationshipWithLinks_encode", test_ToManyRelationshipWithLinks_encode),
+        ("test_ToManyRelationshipWithMeta", test_ToManyRelationshipWithMeta),
+        ("test_ToManyRelationshipWithMeta_encode", test_ToManyRelationshipWithMeta_encode),
+        ("test_ToManyRelationshipWithMetaAndLinks", test_ToManyRelationshipWithMetaAndLinks),
+        ("test_ToManyRelationshipWithMetaAndLinks_encode", test_ToManyRelationshipWithMetaAndLinks_encode),
         ("test_ToManyTypeMismatch", test_ToManyTypeMismatch),
         ("test_ToOneRelationship", test_ToOneRelationship),
         ("test_ToOneRelationship_encode", test_ToOneRelationship_encode),
+        ("test_ToOneRelationshipWithLinks", test_ToOneRelationshipWithLinks),
+        ("test_ToOneRelationshipWithLinks_encode", test_ToOneRelationshipWithLinks_encode),
+        ("test_ToOneRelationshipWithMeta", test_ToOneRelationshipWithMeta),
+        ("test_ToOneRelationshipWithMeta_encode", test_ToOneRelationshipWithMeta_encode),
+        ("test_ToOneRelationshipWithMetaAndLinks", test_ToOneRelationshipWithMetaAndLinks),
+        ("test_ToOneRelationshipWithMetaAndLinks_encode", test_ToOneRelationshipWithMetaAndLinks_encode),
         ("test_ToOneTypeMismatch", test_ToOneTypeMismatch),
     ]
 }
@@ -317,6 +331,7 @@ extension Relationship_LiteralTests {
 
 extension ResourceBodyTests {
     static let __allTests = [
+        ("test_initializers", test_initializers),
         ("test_manyResourceBody", test_manyResourceBody),
         ("test_manyResourceBody_encode", test_manyResourceBody_encode),
         ("test_manyResourceBodyEmpty", test_manyResourceBodyEmpty),