update linuxmain

JSONAPI.playground/Pages/Test Library.xcplaygroundpage/Contents.swift

@@ -0,0 +1,24 @@
+//: [Previous](@previous)
+
+import Foundation
+import JSONAPI
+import JSONAPITestLib
+
+/*******
+
+Please enjoy these examples, but allow me the forced casting and the lack of error checking for the sake of brevity.
+
+********/
+
+// MARK: - Literal Expressibility
+// The JSONAPITestLib provides literal expressibility for key types to
+// make creating tests easier
+let dog = Dog(id: "1234", attributes: Dog.Attributes(name: "Buddy"), relationships: Dog.Relationships(owner: nil))
+
+// MARK: - JSON API structure checking
+// The JSONAPITestLib provides a `check` function for each Entity type
+// that uses reflection to catch mistakes that are not forbidden by
+// Swift's type system but will result in unexpected results when
+// encoding/decoding. It is a good idea to add a `check` to each of
+// your unit tests that create Entities.
+try Dog.check(dog)

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

@@ -11,7 +11,7 @@ Please enjoy these examples, but allow me the forced casting and the lack of err
 // MARK: - Create a request or response body with one Dog in it
 let dogFromCode = try! Dog(name: "Buddy", owner: nil)
 
-typealias SingleDogDocument = JSONAPIDocument<SingleResourceBody<Dog>, NoIncludes, BasicJSONAPIError>
+typealias SingleDogDocument = JSONAPI.Document<SingleResourceBody<Dog>, NoMetadata, NoLinks, NoIncludes, UnknownJSONAPIError>
 
 let singleDogDocument = SingleDogDocument(body: SingleResourceBody(entity: dogFromCode))
 
@@ -19,7 +19,7 @@ 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.data?.primary.value
+let dogFromData = dogResponse.body.primaryData?.value
 
 // MARK: - Create a request or response with multiple people and dogs and houses included
 let personIds = [Person.Identifier(), Person.Identifier()]
@@ -27,7 +27,7 @@ let dogs = try! [Dog(name: "Buddy", owner: personIds[0]), Dog(name: "Joy", owner
 let houses = [House(), House()]
 let people = try! [Person(id: personIds[0], name: ["Gary", "Doe"], favoriteColor: "Orange-Red", friends: [], dogs: [dogs[0], dogs[1]], home: houses[0]), Person(id: personIds[1], name: ["Elise", "Joy"], favoriteColor: "Red", friends: [], dogs: [dogs[2]], home: houses[1])]
 
-typealias BatchPeopleDocument = JSONAPIDocument<ManyResourceBody<Person>, Include2<Dog, House>, BasicJSONAPIError>
+typealias BatchPeopleDocument = JSONAPI.Document<ManyResourceBody<Person>, NoMetadata, NoLinks, Include2<Dog, House>, UnknownJSONAPIError>
 
 let includes = dogs.map { BatchPeopleDocument.Include($0) } + houses.map { BatchPeopleDocument.Include($0) }
 let batchPeopleDocument = BatchPeopleDocument(body: .init(entities: people), includes: .init(values: includes))
@@ -36,6 +36,28 @@ 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.data?.primary.values
-let dogsFromData = peopleResponse.body.data?.included[Dog.self]
-let housesFromData = peopleResponse.body.data?.included[House.self]
+let peopleFromData = peopleResponse.body.primaryData?.values
+let dogsFromData = peopleResponse.body.includes?[Dog.self]
+let housesFromData = peopleResponse.body.includes?[House.self]
+
+print("-----")
+print(peopleResponse)
+print("-----")
+
+// MARK: - Pass successfully parsed body to other parts of the code
+
+if case let .data(bodyData) = peopleResponse.body {
+	print("first person's name: \(bodyData.primary.values[0][\.fullName])")
+} else {
+	print("no body data")
+}
+
+// MARK: - Work in the abstract
+
+func process<T: JSONAPIDocument>(document: T) {
+	guard case let .data(body) = document.body else {
+		return
+	}
+	let x: T.BodyData = body
+}
+process(document: peopleResponse)

JSONAPI.playground/Sources/Entities.swift

@@ -24,7 +24,7 @@ extension String: CreatableRawIdType {
 }
 
 // MARK: - Entity typealias for convenience
-public typealias ExampleEntity<Description: EntityDescription> = Entity<Description, Id<String, Description>>
+public typealias ExampleEntity<Description: EntityDescription> = Entity<Description, String>
 
 // MARK: - A few resource objects (entities)
 public enum PersonDescription: EntityDescription {
@@ -34,20 +34,35 @@ public enum PersonDescription: EntityDescription {
 	public struct Attributes: JSONAPI.Attributes {
 		public let name: Attribute<[String]>
 		public let favoriteColor: Attribute<String>
+
+		public var fullName: Attribute<String> {
+			return name.map { $0.joined(separator: " ") }
+		}
+
+		public init(name: Attribute<[String]>, favoriteColor: Attribute<String>) {
+			self.name = name
+			self.favoriteColor = favoriteColor
+		}
 	}
 	
 	public struct Relationships: JSONAPI.Relationships {
 		public let friends: ToManyRelationship<Person>
 		public let dogs: ToManyRelationship<Dog>
 		public let home: ToOneRelationship<House>
+
+		public init(friends: ToManyRelationship<Person>, dogs: ToManyRelationship<Dog>, home: ToOneRelationship<House>) {
+			self.friends = friends
+			self.dogs = dogs
+			self.home = home
+		}
 	}
 }
 
 public typealias Person = ExampleEntity<PersonDescription>
 
-public extension Entity where Description == PersonDescription, Identifier == Id<String, PersonDescription> {
-	public init(id: Person.Identifier? = nil,name: [String], favoriteColor: String, friends: [Person], dogs: [Dog], home: House) throws {
-		self = try Person(id: id ?? Person.Identifier(), attributes: .init(name: .init(rawValue: name), favoriteColor: .init(rawValue: favoriteColor)), relationships: .init(friends: .init(entities: friends), dogs: .init(entities: dogs), home: .init(entity: home)))
+public extension Entity where Description == PersonDescription, 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)))
 	}
 }
 
@@ -57,21 +72,29 @@ public enum DogDescription: EntityDescription {
 
 	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 owner: ToOneRelationship<Person?>
+
+		public init(owner: ToOneRelationship<Person?>) {
+			self.owner = owner
+		}
 	}
 }
 
 public typealias Dog = ExampleEntity<DogDescription>
 
-public extension Entity where Description == DogDescription, Identifier == Id<String, DogDescription> {
+public extension Entity where Description == DogDescription, 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)))
 	}
 
-	public init(name: String, owner: Person.Identifier) throws {
+	public init(name: String, owner: Person.Id) throws {
 		self = try Dog(attributes: .init(name: .init(rawValue: name)), relationships: .init(owner: .init(id: owner)))
 	}
 }
@@ -81,7 +104,7 @@ public enum HouseDescription: EntityDescription {
 	public static var type: String { return "houses" }
 
 	public typealias Attributes = NoAttributes
-	public typealias Relationships = NoRelatives
+	public typealias Relationships = NoRelationships
 }
 
 public typealias House = ExampleEntity<HouseDescription>

JSONAPI.playground/contents.xcplayground

@@ -1,4 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
-<playground version='5.0' target-platform='macos' executeOnSourceChanges='false'>
-    <timeline fileName='timeline.xctimeline'/>
+<playground version='6.0' target-platform='macos' executeOnSourceChanges='false'>
+    <pages>
+        <page name='Test Library'/>
+        <page name='Usage'/>
+    </pages>
 </playground>

Package.swift

@@ -6,23 +6,27 @@ import PackageDescription
 let package = Package(
     name: "JSONAPI",
     products: [
-        // Products define the executables and libraries produced by a package, and make them visible to other packages.
         .library(
             name: "JSONAPI",
             targets: ["JSONAPI"]),
+		.library(
+			name: "JSONAPITestLib",
+			targets: ["JSONAPITestLib"])
     ],
     dependencies: [
+		// antitypical/Result without the Foundation requirement:
         .package(url: "https://github.com/mattpolzin/Result", .branch("master"))
     ],
     targets: [
-        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
-        // Targets can depend on other targets in this package, and on products in packages which this package depends on.
         .target(
             name: "JSONAPI",
             dependencies: ["Result"]),
+		.target(
+			name: "JSONAPITestLib",
+			dependencies: ["JSONAPI"]),
         .testTarget(
             name: "JSONAPITests",
-            dependencies: ["JSONAPI"]),
+            dependencies: ["JSONAPITestLib"])
     ],
   	swiftLanguageVersions: [.v4_2]
 )

README.md

@@ -13,6 +13,19 @@ The primary goals of this framework are:
 3. Do not sacrifice type safety.
 4. Be platform agnostic so that Swift code can be written once and used by both the client and the server.
 
+### Caveat
+The big caveat is that, although the aim is to support the JSON API spec, this framework ends up being _naturally_ opinionated about certain things that the API Spec does not specify. These caveats are largely a side effect of attempting to write the library in a "Swifty" way.
+
+If you find that something in the JSON API v1.0 Spec is not explicitly missing from the **Project Status** checklist but this library does not support it, please let me know! I want to keep working towards a library implementation that is useful in any application.
+
+## Dev Environment
+### Prerequisites
+1. Swift 4.2+ and Swift Package Manager
+
+### Xcode project
+To create an Xcode project for JSONAPI, run
+`swift package generate-xcodeproj`
+
 ## Project Status
 
 ### Decoding
@@ -67,10 +80,10 @@ The primary goals of this framework are:
 - [x] `href`
 - [x] `meta`
 
-### EntityDescription Validator (using reflection)
-- [ ] Disallow optional array in `Attribute` and `Relationship` (should be empty array, not `null`).
-- [ ] Only allow `Attribute` and `TransformAttribute` within `Attributes` struct.
-- [ ] Only allow `ToManyRelationship` and `ToOneRelationship` within `Relationships` struct.
+### Entity Validator (using reflection)
+- [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 `ToManyRelationship` and `ToOneRelationship` within `Relationships` struct.
 
 ### Strict Decoding/Encoding Settings
 - [ ] Error (potentially while still encoding/decoding successfully) if an included entity is not related to a primary entity (Turned off by default).
@@ -86,10 +99,10 @@ The primary goals of this framework are:
 - [ ] Property-based testing (using `SwiftCheck`)
 - [x] Roll my own `Result` or find an alternative that doesn't use `Foundation`.
 - [ ] Create more descriptive errors that are easier to use for troubleshooting.
+- [x] Make it easier to construct `Attributes` and `Relationships` values in test cases (literal expressibility).
+- [x] Make `TransformedAttribute` a Functor.
 
 ## Usage
-### Prerequisites
-1. Swift 4.2+ and Swift Package Manager
 
 ### `EntityDescription`
 
@@ -113,7 +126,7 @@ enum PersonDescription: IdentifiedEntityDescription {
 The requirements of an `EntityDescription` are:
 1. A static `var` "type" that matches the JSON type; The JSON spec requires every *Resource Object* to have a "type".
 2. A `struct` of `Attributes` **- OR -** `typealias Attributes = NoAttributes`
-3. A `struct` of `Relationships` **- OR -** `typealias Relationships = NoRelatives`
+3. A `struct` of `Relationships` **- OR -** `typealias Relationships = NoRelationships`
 
 Note that an `enum` type is used here for the `EntityDescription`; it could have been a `struct`, but `EntityDescription`s do not ever need to be created so an `enum` with no `case`s is a nice fit for the job.
 
@@ -157,13 +170,13 @@ An `Entity` needs to be specialized on two generic types. The first is the `Enti
 
 #### `IdType`
 
-An `IdType` packages up two pieces of information: A unique identifier of a given `RawIdType` and the `EntityDescription` of the type of entity the Id identifies. Having the `EntityDescription` type associated with the Id makes it easy to store all of your entities in a local hash broken out by `EntityDescription`; You can pass Ids around and always know where to look for the `Entity` to which the Id refers. `RawIdType`s are documented below.
+An `IdType` packages up two pieces of information: A unique identifier of a given `RawIdType` and the `Entity` type that the Id identifies. Having the `Entity` type associated with the Id makes it easy to store all of your entities in a local hash broken out by `Entity` type; You can pass Ids around and always know where to look for the `Entity` to which the Id refers. `RawIdType`s are documented below.
 
 #### Convenient `typealiases`
 
 Often you can use one `RawIdType` for many if not all of your `Entities`. That means you can save yourself some boilerplate by using `typealias`es like the following:
 ```
-public typealias Entity<Description: JSONAPI.EntityDescription> = JSONAPI.Entity<Description, Id<String, Description>>
+public typealias Entity<Description: JSONAPI.EntityDescription> = JSONAPI.Entity<Description, String>
 
 public typealias NewEntity<Description: JSONAPI.EntityDescription> = JSONAPI.Entity<Description, Unidentified>
 ```
@@ -188,7 +201,7 @@ let nullableRelative: ToOneRelationship<Person?>
 
 An entity that does not have relationships can be described by adding the following to an `EntityDescription`:
 ```
-typealias Relationships = NoRelatives
+typealias Relationships = NoRelationships
 ```
 
 `Relationship`s boil down to Ids of other entities. To access the Id of a related entity, you can use the shorthand `~>` operator with the `KeyPath` of the `Relationship` from which you want the Id. The friends of the above `Person` entity could be accessed as follows (type annotations for clarity):
@@ -244,13 +257,23 @@ Note that the first generic parameter of `TransformAttribute` is the type you ex
 
 You can also creator `Validator`s and `ValidatedAttribute`s. A `Validator` is just a `Transformer` that by convention does not perform a transformation. It simply `throws` if an attribute value is invalid.
 
+#### 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.
+
+```
+public var fullName: Attribute<String> {
+	return name.map { $0.joined(separator: " ") }
+}
+```
+
 ### `JSONAPIDocument`
 
 The entirety of a JSON API request or response is encoded or decoded from- or to a `JSONAPIDocument`. As an example, a JSON API response containing one `Person` and no included entities could be decoded as follows:
 ```
 let decoder = JSONDecoder()
 
-let responseStructure = JSONAPIDocument<SingleResourceBody<Person>, NoMetadata, NoLinks, NoIncludes, BasicJSONAPIError>.self
+let responseStructure = JSONAPIDocument<SingleResourceBody<Person>, NoMetadata, NoLinks, NoIncludes, UnknownJSONAPIError>.self
 
 let document = try decoder.decode(responseStructure, from: data)
 ```
@@ -279,9 +302,9 @@ The second generic type of a `JSONAPIDocument` is a `Meta`. This structure is en
 You would then create the following `Meta` type:
 ```
 struct PageMetadata: JSONAPI.Meta {
-		let total: Int
-		let limit: Int
-		let offset: Int
+	let total: Int
+	let limit: Int
+	let offset: Int
 }
 ```
 
@@ -321,3 +344,6 @@ extension String: CreatableRawIdType {
 	}
 }
 ```
+
+# JSONAPITestLib
+JSONAPI comes with a test library to help you test your JSON API 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

@@ -5,6 +5,18 @@
 //  Created by Mathew Polzin on 11/5/18.
 //
 
+public protocol JSONAPIDocument: Codable, Equatable {
+	associatedtype PrimaryResourceBody: JSONAPI.ResourceBody
+	associatedtype MetaType: JSONAPI.Meta
+	associatedtype LinksType: JSONAPI.Links
+	associatedtype IncludeType: JSONAPI.Include
+	associatedtype Error: JSONAPIError
+
+	typealias Body = Document<PrimaryResourceBody, MetaType, LinksType, IncludeType, Error>.Body
+
+	var body: Body { get }
+}
+
 /// A JSON API Document represents the entire body
 /// of a JSON API request or the entire body of
 /// a JSON API response.
@@ -12,7 +24,7 @@
 /// API uses snake case, you will want to use
 /// a conversion such as the one offerred by the
 /// Foundation JSONEncoder/Decoder: `KeyDecodingStrategy`
-public struct JSONAPIDocument<ResourceBody: JSONAPI.ResourceBody, MetaType: JSONAPI.Meta, LinksType: JSONAPI.Links, IncludeType: JSONAPI.Include, Error: JSONAPIError>: Equatable {
+public struct Document<PrimaryResourceBody: JSONAPI.ResourceBody, MetaType: JSONAPI.Meta, LinksType: JSONAPI.Links, IncludeType: JSONAPI.Include, Error: JSONAPIError>: JSONAPIDocument {
 	public typealias Include = IncludeType
 
 	public let body: Body
@@ -20,7 +32,21 @@ public struct JSONAPIDocument<ResourceBody: JSONAPI.ResourceBody, MetaType: JSON
 	
 	public enum Body: Equatable {
 		case errors([Error], meta: MetaType?, links: LinksType?)
-		case data(primary: ResourceBody, included: Includes<Include>, meta: MetaType, links: LinksType)
+		case data(Data)
+
+		public struct Data: Equatable {
+			public let primary: PrimaryResourceBody
+			public let includes: Includes<Include>
+			public let meta: MetaType
+			public let links: LinksType
+
+			public init(primary: PrimaryResourceBody, includes: Includes<Include>, meta: MetaType, links: LinksType) {
+				self.primary = primary
+				self.includes = includes
+				self.meta = meta
+				self.links = links
+			}
+		}
 
 		public var isError: Bool {
 			guard case .errors = self else { return false }
@@ -32,20 +58,21 @@ public struct JSONAPIDocument<ResourceBody: JSONAPI.ResourceBody, MetaType: JSON
 			return errors
 		}
 		
-		public var primaryData: ResourceBody? {
-			guard case let .data(primary: body, included: _, meta: _, links: _) = self else { return nil }
-			return body
+		public var primaryData: PrimaryResourceBody? {
+			guard case let .data(data) = self else { return nil }
+			return data.primary
 		}
 
 		public var includes: Includes<Include>? {
-			guard case let .data(primary: _, included: includes, meta: _, links: _) = self else { return nil }
-			return includes
+			guard case let .data(data) = self else { return nil }
+			return data.includes
 		}
 
 		public var meta: MetaType? {
 			switch self {
-			case .data(primary: _, included: _, meta: let metadata, links: _),
-				 .errors(_, meta: let metadata?, links: _):
+			case .data(let data):
+				return data.meta
+			case .errors(_, meta: let metadata?, links: _):
 				return metadata
 			default:
 				return nil
@@ -54,8 +81,9 @@ public struct JSONAPIDocument<ResourceBody: JSONAPI.ResourceBody, MetaType: JSON
 
 		public var links: LinksType? {
 			switch self {
-			case .data(primary: _, included: _, meta: _, links: let links),
-				 .errors(_, meta: _, links: let links?):
+			case .data(let data):
+				return data.links
+			case .errors(_, meta: _, links: let links?):
 				return links
 			default:
 				return nil
@@ -67,54 +95,54 @@ public struct JSONAPIDocument<ResourceBody: JSONAPI.ResourceBody, MetaType: JSON
 		body = .errors(errors, meta: meta, links: links)
 	}
 
-	public init(body: ResourceBody, includes: Includes<Include>, meta: MetaType, links: LinksType) {
-		self.body = .data(primary: body, included: includes, meta: meta, links: links)
+	public init(body: PrimaryResourceBody, includes: Includes<Include>, meta: MetaType, links: LinksType) {
+		self.body = .data(.init(primary: body, includes: includes, meta: meta, links: links))
 	}
 }
 
-extension JSONAPIDocument where IncludeType == NoIncludes {
-	public init(body: ResourceBody, meta: MetaType, links: LinksType) {
-		self.body = .data(primary: body, included: .none, meta: meta, links: links)
+extension Document where IncludeType == NoIncludes {
+	public init(body: PrimaryResourceBody, meta: MetaType, links: LinksType) {
+		self.body = .data(.init(primary: body, includes: .none, meta: meta, links: links))
 	}
 }
 
-extension JSONAPIDocument where MetaType == NoMetadata {
-	public init(body: ResourceBody, includes: Includes<Include>, links: LinksType) {
-		self.body = .data(primary: body, included: includes, meta: .none, links: links)
+extension Document where MetaType == NoMetadata {
+	public init(body: PrimaryResourceBody, includes: Includes<Include>, links: LinksType) {
+		self.body = .data(.init(primary: body, includes: includes, meta: .none, links: links))
 	}
 }
 
-extension JSONAPIDocument where LinksType == NoLinks {
-	public init(body: ResourceBody, includes: Includes<Include>, meta: MetaType) {
-		self.body = .data(primary: body, included: includes, meta: meta, links: .none)
+extension Document where LinksType == NoLinks {
+	public init(body: PrimaryResourceBody, includes: Includes<Include>, meta: MetaType) {
+		self.body = .data(.init(primary: body, includes: includes, meta: meta, links: .none))
 	}
 }
 
-extension JSONAPIDocument where IncludeType == NoIncludes, LinksType == NoLinks {
-	public init(body: ResourceBody, meta: MetaType) {
-		self.body = .data(primary: body, included: .none, meta: meta, links: .none)
+extension Document where IncludeType == NoIncludes, LinksType == NoLinks {
+	public init(body: PrimaryResourceBody, meta: MetaType) {
+		self.body = .data(.init(primary: body, includes: .none, meta: meta, links: .none))
 	}
 }
 
-extension JSONAPIDocument where IncludeType == NoIncludes, MetaType == NoMetadata {
-	public init(body: ResourceBody, links: LinksType) {
-		self.body = .data(primary: body, included: .none, meta: .none, links: links)
+extension Document where IncludeType == NoIncludes, MetaType == NoMetadata {
+	public init(body: PrimaryResourceBody, links: LinksType) {
+		self.body = .data(.init(primary: body, includes: .none, meta: .none, links: links))
 	}
 }
 
-extension JSONAPIDocument where MetaType == NoMetadata, LinksType == NoLinks {
-	public init(body: ResourceBody, includes: Includes<Include>) {
-		self.body = .data(primary: body, included: includes, meta: .none, links: .none)
+extension Document where MetaType == NoMetadata, LinksType == NoLinks {
+	public init(body: PrimaryResourceBody, includes: Includes<Include>) {
+		self.body = .data(.init(primary: body, includes: includes, meta: .none, links: .none))
 	}
 }
 
-extension JSONAPIDocument where IncludeType == NoIncludes, MetaType == NoMetadata, LinksType == NoLinks {
-	public init(body: ResourceBody) {
-		self.body = .data(primary: body, included: .none, meta: .none, links: .none)
+extension Document where IncludeType == NoIncludes, MetaType == NoMetadata, LinksType == NoLinks {
+	public init(body: PrimaryResourceBody) {
+		self.body = .data(.init(primary: body, includes: .none, meta: .none, links: .none))
 	}
 }
 
-extension JSONAPIDocument: Codable {
+extension Document {
 	private enum RootCodingKeys: String, CodingKey {
 		case data
 		case errors
@@ -157,11 +185,11 @@ extension JSONAPIDocument: Codable {
 			return
 		}
 
-		let data: ResourceBody
-		if let noData = NoResourceBody() as? ResourceBody {
+		let data: PrimaryResourceBody
+		if let noData = NoResourceBody() as? PrimaryResourceBody {
 			data = noData
 		} else {
-			data = try container.decode(ResourceBody.self, forKey: .data)
+			data = try container.decode(PrimaryResourceBody.self, forKey: .data)
 		}
 
 		let maybeIncludes = try container.decodeIfPresent(Includes<Include>.self, forKey: .included)
@@ -175,7 +203,7 @@ extension JSONAPIDocument: Codable {
 			throw JSONAPIEncodingError.missingOrMalformedLinks
 		}
 		
-		body = .data(primary: data, included: maybeIncludes ?? Includes<Include>.none, meta: metaVal, links: linksVal)
+		body = .data(.init(primary: data, includes: maybeIncludes ?? Includes<Include>.none, meta: metaVal, links: linksVal))
 	}
 
 	public func encode(to encoder: Encoder) throws {
@@ -199,19 +227,19 @@ extension JSONAPIDocument: Codable {
 				try container.encode(linksVal, forKey: .links)
 			}
 
-		case .data(primary: let resourceBody, included: let includes, let meta, links: let links):
-			try container.encode(resourceBody, forKey: .data)
+		case .data(let data):
+			try container.encode(data.primary, forKey: .data)
 
 			if Include.self != NoIncludes.self {
-				try container.encode(includes, forKey: .included)
+				try container.encode(data.includes, forKey: .included)
 			}
 
 			if MetaType.self != NoMetadata.self {
-				try container.encode(meta, forKey: .meta)
+				try container.encode(data.meta, forKey: .meta)
 			}
 
 			if LinksType.self != NoLinks.self {
-				try container.encode(links, forKey: .links)
+				try container.encode(data.links, forKey: .links)
 			}
 		}
 	}
@@ -219,8 +247,25 @@ extension JSONAPIDocument: Codable {
 
 // MARK: - CustomStringConvertible
 
-extension JSONAPIDocument: CustomStringConvertible {
+extension Document: CustomStringConvertible {
 	public var description: String {
-		return "JSONAPIDocument(body: \(String(describing: body))"
+		return "Document(\(String(describing: body)))"
+	}
+}
+
+extension Document.Body: CustomStringConvertible {
+	public var description: String {
+		switch self {
+		case .errors(let errors, meta: let meta, links: let links):
+			return "errors: \(String(describing: errors)), meta: \(String(describing: meta)), links: \(String(describing: links))"
+		case .data(let data):
+			return String(describing: data)
+		}
+	}
+}
+
+extension Document.Body.Data: CustomStringConvertible {
+	public var description: String {
+		return "primary: \(String(describing: primary)), includes: \(String(describing: includes)), meta: \(String(describing: meta)), links: \(String(describing: links))"
 	}
 }

Sources/JSONAPI/Document/Error.swift

@@ -9,7 +9,7 @@ public protocol JSONAPIError: Swift.Error, Equatable, Codable {
 	static var unknown: Self { get }
 }
 
-public enum BasicJSONAPIError: JSONAPIError {
+public enum UnknownJSONAPIError: JSONAPIError {
 	case unknownError
 	
 	public init(from decoder: Decoder) throws {
@@ -21,7 +21,7 @@ public enum BasicJSONAPIError: JSONAPIError {
 		try container.encode("unknown")
 	}
 	
-	public static var unknown: BasicJSONAPIError {
+	public static var unknown: UnknownJSONAPIError {
 		return .unknownError
 	}
 }

Sources/JSONAPI/Document/ResourceBody.swift

@@ -1,5 +1,5 @@
 //
-//  ResourceBody.swift
+//  PrimaryResourceBody.swift
 //  JSONAPI
 //
 //  Created by Mathew Polzin on 11/10/18.
@@ -18,7 +18,7 @@ public struct SingleResourceBody<Entity: JSONAPI.PrimaryResource>: ResourceBody
 	}
 }
 
-public struct ManyResourceBody<Entity: JSONAPI.EntityType>: ResourceBody {
+public struct ManyResourceBody<Entity: JSONAPI.PrimaryResource>: ResourceBody {
 	public let values: [Entity]
 
 	public init(entities: [Entity]) {
@@ -32,7 +32,7 @@ public struct NoResourceBody: ResourceBody {
 	public static var none: NoResourceBody { return NoResourceBody() }
 }
 
-// MARK: Decodable
+// MARK: Codable
 extension SingleResourceBody {
 	public init(from decoder: Decoder) throws {
 		let container = try decoder.singleValueContainer()
@@ -80,12 +80,12 @@ extension ManyResourceBody {
 
 extension SingleResourceBody: CustomStringConvertible {
 	public var description: String {
-		return "ResourceBody(\(String(describing: value)))"
+		return "PrimaryResourceBody(\(String(describing: value)))"
 	}
 }
 
 extension ManyResourceBody: CustomStringConvertible {
 	public var description: String {
-		return "ResourceBody(\(String(describing: values)))"
+		return "PrimaryResourceBody(\(String(describing: values)))"
 	}
 }

Sources/JSONAPI/Meta/Links.swift

@@ -9,14 +9,16 @@
 public protocol Links: Codable, Equatable {}
 
 /// Use NoLinks where no links should belong to a JSON API component
-public struct NoLinks: Links {
+public struct NoLinks: Links, CustomStringConvertible {
 	public static var none: NoLinks { return NoLinks() }
 	public init() {}
+
+	public var description: String { return "No Links" }
 }
 
-public protocol URL: Codable, Equatable {}
+public protocol JSONAPIURL: Codable, Equatable {}
 
-public struct Link<URL: JSONAPI.URL, Meta: JSONAPI.Meta>: Equatable, Codable {
+public struct Link<URL: JSONAPI.JSONAPIURL, Meta: JSONAPI.Meta>: Equatable, Codable {
 	public let url: URL
 	public let meta: Meta
 }

Sources/JSONAPI/Meta/Meta.swift

@@ -19,8 +19,10 @@ public protocol Meta: Codable, Equatable {
 // nullable.
 extension Optional: Meta where Wrapped: Meta {}
 
-public struct NoMetadata: Meta {
+public struct NoMetadata: Meta, CustomStringConvertible {
 	public static var none: NoMetadata { return NoMetadata() }
 
 	public init() { }
+
+	public var description: String { return "No Metadata" }
 }

Sources/JSONAPI/Resource/Attribute+Functor.swift

@@ -0,0 +1,21 @@
+//
+//  Attribute+Functor.swift
+//  JSONAPI
+//
+//  Created by Mathew Polzin on 11/28/18.
+//
+
+public extension TransformedAttribute {
+	/// Map an Attribute to a new wrapped type.
+	/// Note that the resulting Attribute will have no transformer, even if the
+	/// source Attribute has a transformer.
+	/// You are mapping the output of the source transform into
+	/// the RawValue of a new transformerless Attribute.
+	///
+	/// Generally, this is the most useful operation. The transformer gives you
+	/// control over the decoding of the Attribute, but once the Attribute exists,
+	/// mapping on it is most useful for creating computed Attribute properties.
+	public func map<T: Codable>(_ transform: (Transformer.To) throws -> T) rethrows -> Attribute<T> {
+		return Attribute<T>(value: try transform(value))
+	}
+}

Sources/JSONAPI/Resource/Attribute.swift

@@ -5,7 +5,10 @@
 //  Created by Mathew Polzin on 11/13/18.
 //
 
-public struct TransformedAttribute<RawValue: Codable, Transformer: JSONAPI.Transformer>: Codable where Transformer.From == RawValue {
+public protocol AttributeType: Codable {
+}
+
+public struct TransformedAttribute<RawValue: Codable, Transformer: JSONAPI.Transformer>: AttributeType where Transformer.From == RawValue {
 	private let rawValue: RawValue
 	
 	public let value: Transformer.To
@@ -16,6 +19,13 @@ public struct TransformedAttribute<RawValue: Codable, Transformer: JSONAPI.Trans
 	}
 }
 
+extension TransformedAttribute where Transformer: ReversibleTransformer {
+	public init(transformedValue: Transformer.To) throws {
+		self.value = transformedValue
+		rawValue = try Transformer.reverse(value)
+	}
+}
+
 extension TransformedAttribute: CustomStringConvertible {
 	public var description: String {
 		return "Attribute<\(String(describing: Transformer.From.self)) -> \(String(describing: Transformer.To.self))>(\(String(describing: value)))"
@@ -24,6 +34,15 @@ extension TransformedAttribute: CustomStringConvertible {
 
 extension TransformedAttribute: Equatable where Transformer.From: Equatable, Transformer.To: Equatable {}
 
+extension TransformedAttribute where Transformer == IdentityTransformer<RawValue> {
+	// If we are using the identity transform, we can skip the transform and guarantee no
+	// error is thrown.
+	public init(value: RawValue) {
+		rawValue = value
+		self.value = value
+	}
+}
+
 public typealias ValidatedAttribute<RawValue: Codable, Validator: JSONAPI.Validator> = TransformedAttribute<RawValue, Validator> where RawValue == Validator.From
 
 public typealias Attribute<T: Codable> = TransformedAttribute<T, IdentityTransformer<T>>

Sources/JSONAPI/Resource/Entity.swift

@@ -16,11 +16,15 @@ public typealias Attributes = Codable & Equatable
 
 /// Can be used as `Relationships` Type for Entities that do not
 /// have any Relationships.
-public struct NoRelatives: Relationships {}
+public struct NoRelationships: Relationships {
+	public static var none: NoRelationships { return .init() }
+}
 
 /// Can be used as `Attributes` Type for Entities that do not
 /// have any Attributes.
-public struct NoAttributes: Attributes {}
+public struct NoAttributes: Attributes {
+	public static var none: NoAttributes { return .init() }
+}
 
 /// An `EntityDescription` describes a JSON API
 /// Resource Object. The Resource Object
@@ -34,28 +38,54 @@ public protocol EntityDescription {
 	static var type: String { get }
 }
 
+/// 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 {
+	associatedtype Description: EntityDescription
+	associatedtype EntityRawIdType: JSONAPI.MaybeRawId
+
+	typealias Id = JSONAPI.Id<EntityRawIdType, Self>
+
+	typealias Attributes = Description.Attributes
+	typealias Relationships = Description.Relationships
+
+	/// 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,
+	/// this should be of a type conforming to `IdType`.
+	var id: Id { get }
+
+	/// The JSON API compliant attributes of this `Entity`.
+	var attributes: Attributes { get }
+
+	/// The JSON API compliant relationships of this `Entity`.
+	var relationships: Relationships { get }
+}
+
+extension EntityProxy {
+	/// The JSON API compliant "type" of this `Entity`.
+	public static var type: String { return Description.type }
+}
+
 /// EntityType is the protocol that Entity conforms to. This
 /// protocol lets other types accept any Entity as a generic
 /// specialization.
-public protocol EntityType: PrimaryResource {
-	associatedtype Description: EntityDescription
-	associatedtype Identifier: Equatable & Codable
+public protocol EntityType: EntityProxy, PrimaryResource {
 }
 
+public protocol IdentifiableEntityType: EntityType, Relatable where EntityRawIdType: JSONAPI.RawIdType {}
+
 /// An `Entity` is a single model type that can be
 /// encoded to or decoded from a JSON API
 /// "Resource Object."
 /// See https://jsonapi.org/format/#document-resource-objects
-public struct Entity<Description: JSONAPI.EntityDescription, Identifier: JSONAPI.Identifier>: EntityType {
-	
-	/// The JSON API compliant "type" of this `Entity`.
-	public static var type: String { return Description.type }
-	
+public struct Entity<Description: JSONAPI.EntityDescription, EntityRawIdType: JSONAPI.MaybeRawId>: EntityType {
 	/// 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,
 	/// this should be of a type conforming to `IdType`.
-	public let id: Identifier
+	public let id: Entity.Id
 	
 	/// The JSON API compliant attributes of this `Entity`.
 	public let attributes: Description.Attributes
@@ -63,13 +93,18 @@ public struct Entity<Description: JSONAPI.EntityDescription, Identifier: JSONAPI
 	/// The JSON API compliant relationships of this `Entity`.
 	public let relationships: Description.Relationships
 	
-	public init(id: Identifier, attributes: Description.Attributes, relationships: Description.Relationships) {
+	public init(id: Entity.Id, attributes: Description.Attributes, relationships: Description.Relationships) {
 		self.id = id
 		self.attributes = attributes
 		self.relationships = relationships
 	}
 }
 
+extension Entity: IdentifiableEntityType, Relatable, WrappedRelatable where EntityRawIdType: JSONAPI.RawIdType {
+	public typealias Identifier = Entity.Id
+	public typealias WrappedIdentifier = Identifier
+}
+
 extension Entity: CustomStringConvertible {
 	public var description: String {
 		return "Entity<\(Entity.type)>(id: \(String(describing: id)), attributes: \(String(describing: attributes)), relationships: \(String(describing: relationships)))"
@@ -77,52 +112,52 @@ extension Entity: CustomStringConvertible {
 }
 
 // MARK: Convenience initializers
-extension Entity where Identifier: CreatableIdType {
+extension Entity where EntityRawIdType: CreatableRawIdType {
 	public init(attributes: Description.Attributes, relationships: Description.Relationships) {
-		self.id = Identifier()
+		self.id = Entity.Id()
 		self.attributes = attributes
 		self.relationships = relationships
 	}
 }
 
 extension Entity where Description.Attributes == NoAttributes {
-	public init(id: Identifier, relationships: Description.Relationships) {
+	public init(id: Entity.Id, relationships: Description.Relationships) {
 		self.init(id: id, attributes: NoAttributes(), relationships: relationships)
 	}
 }
 
-extension Entity where Description.Attributes == NoAttributes, Identifier: CreatableIdType {
+extension Entity where Description.Attributes == NoAttributes, EntityRawIdType: CreatableRawIdType {
 	public init(relationships: Description.Relationships) {
 		self.init(attributes: NoAttributes(), relationships: relationships)
 	}
 }
 
-extension Entity where Description.Relationships == NoRelatives {
-	public init(id: Identifier, attributes: Description.Attributes) {
-		self.init(id: id, attributes: attributes, relationships: NoRelatives())
+extension Entity where Description.Relationships == NoRelationships {
+	public init(id: Entity.Id, attributes: Description.Attributes) {
+		self.init(id: id, attributes: attributes, relationships: NoRelationships())
 	}
 }
 
-extension Entity where Description.Relationships == NoRelatives, Identifier: CreatableIdType {
+extension Entity where Description.Relationships == NoRelationships, EntityRawIdType: CreatableRawIdType {
 	public init(attributes: Description.Attributes) {
-		self.init(attributes: attributes, relationships: NoRelatives())
+		self.init(attributes: attributes, relationships: NoRelationships())
 	}
 }
 
-extension Entity where Description.Attributes == NoAttributes, Description.Relationships == NoRelatives {
-	public init(id: Identifier) {
-		self.init(id: id, attributes: NoAttributes(), relationships: NoRelatives())
+extension Entity where Description.Attributes == NoAttributes, Description.Relationships == NoRelationships {
+	public init(id: Entity.Id) {
+		self.init(id: id, attributes: NoAttributes(), relationships: NoRelationships())
 	}
 }
 
-extension Entity where Description.Attributes == NoAttributes, Description.Relationships == NoRelatives, Identifier: CreatableIdType {
+extension Entity where Description.Attributes == NoAttributes, Description.Relationships == NoRelationships, EntityRawIdType: CreatableRawIdType {
 	public init() {
-		self.init(attributes: NoAttributes(), relationships: NoRelatives())
+		self.init(attributes: NoAttributes(), relationships: NoRelationships())
 	}
 }
 
 // MARK: Pointer for Relationships use.
-public extension Entity where Identifier: IdType {
+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> {
@@ -131,21 +166,21 @@ public extension Entity where Identifier: IdType {
 }
 
 // MARK: Attribute Access
-public extension Entity {
+public extension EntityProxy {
 	/// Access the attribute at the given keypath. This just
 	/// allows you to write `entity[\.propertyName]` instead
 	/// of `entity.relationships.propertyName`.
 	subscript<T, TFRM: Transformer>(_ path: KeyPath<Description.Attributes, TransformedAttribute<T, TFRM>>) -> TFRM.To {
 		return attributes[keyPath: path].value
 	}
-	
+
 	/// Access the attribute at the given keypath. This just
 	/// allows you to write `entity[\.propertyName]` instead
 	/// of `entity.relationships.propertyName`.
 	subscript<T, TFRM: Transformer>(_ path: KeyPath<Description.Attributes, TransformedAttribute<T, TFRM>?>) -> TFRM.To? {
 		return attributes[keyPath: path]?.value
 	}
-	
+
 	/// Access the attribute at the given keypath. This just
 	/// allows you to write `entity[\.propertyName]` instead
 	/// of `entity.relationships.propertyName`.
@@ -155,18 +190,18 @@ public extension Entity {
 }
 
 // MARK: Relationship Access
-public extension Entity {
+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: Entity, path: KeyPath<Description.Relationships, ToOneRelationship<OtherEntity>>) -> OtherEntity.WrappedIdentifier {
+	public static func ~><OtherEntity: OptionalRelatable>(entity: Self, path: KeyPath<Description.Relationships, ToOneRelationship<OtherEntity>>) -> 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: Entity, path: KeyPath<Description.Relationships, ToManyRelationship<OtherEntity>>) -> [OtherEntity.Identifier] {
+	public static func ~><OtherEntity: Relatable>(entity: Self, path: KeyPath<Description.Relationships, ToManyRelationship<OtherEntity>>) -> [OtherEntity.Identifier] {
 		return entity.relationships[keyPath: path].ids
 	}
 }
@@ -187,7 +222,7 @@ public extension Entity {
 		
 		try container.encode(Entity.type, forKey: .type)
 		
-		if Identifier.self != Unidentified.self {
+		if EntityRawIdType.self != Unidentified.self {
 			try container.encode(id, forKey: .id)
 		}
 		
@@ -195,7 +230,7 @@ public extension Entity {
 			try container.encode(attributes, forKey: .attributes)
 		}
 		
-		if Description.Relationships.self != NoRelatives.self {
+		if Description.Relationships.self != NoRelationships.self {
 			try container.encode(relationships, forKey: .relationships)
 		}
 	}
@@ -209,11 +244,12 @@ public extension Entity {
 		guard Entity.type == type else {
 			throw JSONAPIEncodingError.typeMismatch(expected: Description.type, found: type)
 		}
-		
-		id = try (Unidentified() as? Identifier) ?? container.decode(Identifier.self, forKey: .id)
+
+		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)
 		
-		relationships = try (NoRelatives() as? Description.Relationships) ?? container.decode(Description.Relationships.self, forKey: .relationships)
+		relationships = try (NoRelationships() as? Description.Relationships) ?? container.decode(Description.Relationships.self, forKey: .relationships)
 	}
 }

Sources/JSONAPI/Resource/Id.swift

@@ -5,10 +5,16 @@
 //  Created by Mathew Polzin on 7/24/18.
 //
 
+/// All types that are RawIdType and additionally
+/// Unidentified conform to this protocol. You
+/// should not add conformance to this protocol
+/// directly.
+public protocol MaybeRawId: Codable, Equatable {}
+
 /// Any type that you would like to be encoded to and
 /// decoded from JSON API ids should conform to this
 /// protocol. Conformance for `String` is given.
-public protocol RawIdType: Codable, Equatable {}
+public protocol RawIdType: MaybeRawId, Hashable {}
 
 /// If you would like to be able to create new
 /// Entities with Ids backed by a RawIdType then
@@ -22,18 +28,18 @@ public protocol CreatableRawIdType: RawIdType {
 
 extension String: RawIdType {}
 
-public protocol Identifier: Codable, Equatable {}
-
-public struct Unidentified: Identifier, CustomStringConvertible {
+public struct Unidentified: MaybeRawId, CustomStringConvertible {
 	public init() {}
 	
-	public var description: String { return "Id(Unidentified)" }
+	public var description: String { return "Unidentified" }
 }
 
-public protocol IdType: Identifier, CustomStringConvertible {
-	associatedtype EntityDescription: JSONAPI.EntityDescription
-	associatedtype RawType: RawIdType
-	
+public protocol MaybeId: Codable {
+	associatedtype EntityType: JSONAPI.EntityProxy
+	associatedtype RawType: MaybeRawId
+}
+
+public protocol IdType: MaybeId, CustomStringConvertible, Hashable where RawType: RawIdType {
 	var rawValue: RawType { get }
 }
 
@@ -47,27 +53,33 @@ public protocol CreatableIdType: IdType {
 
 /// An Entity ID. These IDs can be encoded to or decoded from
 /// JSON API IDs.
-public struct Id<RawType: RawIdType, EntityDescription: JSONAPI.EntityDescription>: IdType {
+public struct Id<RawType: MaybeRawId, EntityType: JSONAPI.EntityProxy>: Codable, Equatable, MaybeId {
 
 	public let rawValue: RawType
 	
 	public init(rawValue: RawType) {
 		self.rawValue = rawValue
 	}
-	
+
 	public init(from decoder: Decoder) throws {
 		let container = try decoder.singleValueContainer()
 		rawValue = try container.decode(RawType.self)
 	}
-	
+
 	public func encode(to encoder: Encoder) throws {
 		var container = encoder.singleValueContainer()
 		try container.encode(rawValue)
 	}
 }
 
+extension Id: Hashable, CustomStringConvertible, IdType where RawType: RawIdType {}
+
 extension Id: CreatableIdType where RawType: CreatableRawIdType {
 	public init() {
 		rawValue = .unique()
 	}
 }
+
+extension Id where RawType == Unidentified {
+	public static var unidentified: Id { return .init(rawValue: Unidentified()) }
+}

Sources/JSONAPI/Resource/Poly.swift

@@ -98,7 +98,7 @@ extension Poly1: CustomStringConvertible {
 		case .a(let a):
 			str = String(describing: a)
 		}
-		return "Include(\(str))"
+		return "Poly(\(str))"
 	}
 }
 
@@ -177,7 +177,7 @@ extension Poly2: CustomStringConvertible {
 		case .b(let b):
 			str = String(describing: b)
 		}
-		return "Include(\(str))"
+		return "Poly(\(str))"
 	}
 }
 
@@ -271,7 +271,7 @@ extension Poly3: CustomStringConvertible {
 		case .c(let c):
 			str = String(describing: c)
 		}
-		return "Include(\(str))"
+		return "Poly(\(str))"
 	}
 }
 
@@ -380,7 +380,7 @@ extension Poly4: CustomStringConvertible {
 		case .d(let d):
 			str = String(describing: d)
 		}
-		return "Include(\(str))"
+		return "Poly(\(str))"
 	}
 }
 
@@ -504,7 +504,7 @@ extension Poly5: CustomStringConvertible {
 		case .e(let e):
 			str = String(describing: e)
 		}
-		return "Include(\(str))"
+		return "Poly(\(str))"
 	}
 }
 
@@ -643,6 +643,6 @@ extension Poly6: CustomStringConvertible {
 		case .f(let f):
 			str = String(describing: f)
 		}
-		return "Include(\(str))"
+		return "Poly(\(str))"
 	}
 }

Sources/JSONAPI/Resource/Relationship.swift

@@ -5,17 +5,15 @@
 //  Created by Mathew Polzin on 8/31/18.
 //
 
+public protocol RelationshipType: Codable {}
+
 /// 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>: Equatable, Codable {
+public struct ToOneRelationship<Relatable: JSONAPI.OptionalRelatable>: RelationshipType, Equatable {
 
 	public let id: Relatable.WrappedIdentifier
-	
-	public var ids: [Relatable.WrappedIdentifier] {
-		return [id]
-	}
 
 	public init(id: Relatable.WrappedIdentifier) {
 		self.id = id
@@ -23,13 +21,13 @@ public struct ToOneRelationship<Relatable: JSONAPI.OptionalRelatable>: Equatable
 }
 
 extension ToOneRelationship where Relatable.WrappedIdentifier == Relatable.Identifier {
-	public init(entity: Entity<Relatable.Description, Relatable.Identifier>) {
+	public init<E: EntityType>(entity: E) where E.Description == Relatable.Description, E.Id == Relatable.Identifier {
 		id = entity.id
 	}
 }
 
-extension ToOneRelationship where Relatable.WrappedIdentifier == Optional<Relatable.Identifier> {
-	public init(entity: Entity<Relatable.Description, Relatable.Identifier>?) {
+extension ToOneRelationship where Relatable.WrappedIdentifier == Relatable.Identifier? {
+	public init<E: EntityType>(entity: E?) where E.Description == Relatable.Description, E.Id == Relatable.Identifier {
 		id = entity?.id
 	}
 }
@@ -38,10 +36,14 @@ extension ToOneRelationship where Relatable.WrappedIdentifier == Optional<Relata
 /// 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>: Equatable, Codable {
+public struct ToManyRelationship<Relatable: JSONAPI.Relatable>: RelationshipType, Equatable {
 
 	public let ids: [Relatable.Identifier]
 
+	public init(ids: [Relatable.Identifier]) {
+		self.ids = ids
+	}
+
 	public init<T: JSONAPI.Relatable>(relationships: [ToOneRelationship<T>]) where T.WrappedIdentifier == Relatable.Identifier {
 		ids = relationships.map { $0.id }
 	}
@@ -56,7 +58,7 @@ public struct ToManyRelationship<Relatable: JSONAPI.Relatable>: Equatable, Codab
 }
 
 extension ToManyRelationship {
-	public init(entities: [Entity<Relatable.Description, Relatable.Identifier>]) {
+	public init<E: EntityType>(entities: [E]) where E.Description == Relatable.Description, E.Id == Relatable.Identifier {
 		ids = entities.map { $0.id }
 	}
 }
@@ -74,10 +76,6 @@ public typealias OptionalRelatable = WrappedRelatable
 /// has an IdType Identifier
 public protocol Relatable: WrappedRelatable {}
 
-extension Entity: Relatable, WrappedRelatable where Identifier: JSONAPI.IdType {
-	public typealias WrappedIdentifier = Identifier
-}
-
 extension Optional: OptionalRelatable where Wrapped: Relatable {
 	public typealias Description = Wrapped.Description
 	public typealias Identifier = Wrapped.Identifier
@@ -182,5 +180,5 @@ extension ToOneRelationship: CustomStringConvertible {
 }
 
 extension ToManyRelationship: CustomStringConvertible {
-	public var description: String { return "Relationship(\(String(describing: ids)))" }
+	public var description: String { return "Relationship([\(ids.map(String.init(describing:)).joined(separator: ", "))])" }
 }

Sources/JSONAPI/Resource/Transformer.swift

@@ -9,11 +9,16 @@ public protocol Transformer {
 	associatedtype From
 	associatedtype To
 
-	static func transform(_ from: From) throws -> To
+	static func transform(_ value: From) throws -> To
 }
 
-public enum IdentityTransformer<T>: Transformer {
-	public static func transform(_ from: T) throws -> T { return from }
+public protocol ReversibleTransformer: Transformer {
+	static func reverse(_ value: To) throws -> From
+}
+
+public enum IdentityTransformer<T>: ReversibleTransformer {
+	public static func transform(_ value: T) throws -> T { return value }
+	public static func reverse(_ value: T) throws -> T { return value }
 }
 
 // MARK: - Validator
@@ -22,10 +27,19 @@ public enum IdentityTransformer<T>: Transformer {
 /// is passed to it but it does not change the type of the value. Any
 /// Transformer will perform validation in one sense so a Validator is
 /// really just semantic sugar (it can provide clarity in its use).
-public protocol Validator: Transformer where From == To {}
+/// To enforce the semantics, any change of the value in your implementation
+/// of `Validator.transform()` will be ignored.
+public protocol Validator: ReversibleTransformer where From == To {
+}
 
 extension Validator {
+	public static func reverse(_ value: To) throws -> To {
+		let _ = try transform(value)
+		return value
+	}
+
 	public static func validate(_ value: To) throws -> To {
-		return try transform(value)
+		let _ = try transform(value)
+		return value
 	}
 }

Sources/JSONAPITestLib/Attribute+Literal.swift

@@ -0,0 +1,96 @@
+
+import JSONAPI
+
+extension TransformedAttribute: ExpressibleByUnicodeScalarLiteral where RawValue: ExpressibleByUnicodeScalarLiteral, Transformer == IdentityTransformer<RawValue> {
+	public typealias UnicodeScalarLiteralType = RawValue.UnicodeScalarLiteralType
+
+	public init(unicodeScalarLiteral value: RawValue.UnicodeScalarLiteralType) {
+		self.init(value: RawValue(unicodeScalarLiteral: value))
+	}
+}
+
+extension TransformedAttribute: ExpressibleByExtendedGraphemeClusterLiteral where RawValue: ExpressibleByExtendedGraphemeClusterLiteral, Transformer == IdentityTransformer<RawValue> {
+	public typealias ExtendedGraphemeClusterLiteralType = RawValue.ExtendedGraphemeClusterLiteralType
+
+	public init(extendedGraphemeClusterLiteral value: RawValue.ExtendedGraphemeClusterLiteralType) {
+		self.init(value: RawValue(extendedGraphemeClusterLiteral: value))
+	}
+}
+
+extension TransformedAttribute: ExpressibleByStringLiteral where RawValue: ExpressibleByStringLiteral, Transformer == IdentityTransformer<RawValue> {
+	public typealias StringLiteralType = RawValue.StringLiteralType
+
+	public init(stringLiteral value: RawValue.StringLiteralType) {
+		self.init(value: RawValue(stringLiteral: value))
+	}
+}
+
+extension TransformedAttribute: ExpressibleByNilLiteral where RawValue: ExpressibleByNilLiteral, Transformer == IdentityTransformer<RawValue> {
+	public init(nilLiteral: ()) {
+		self.init(value: RawValue(nilLiteral: ()))
+	}
+}
+
+extension TransformedAttribute: ExpressibleByFloatLiteral where RawValue: ExpressibleByFloatLiteral, Transformer == IdentityTransformer<RawValue> {
+	public typealias FloatLiteralType = RawValue.FloatLiteralType
+
+	public init(floatLiteral value: RawValue.FloatLiteralType) {
+		self.init(value: RawValue(floatLiteral: value))
+	}
+}
+
+extension TransformedAttribute: ExpressibleByBooleanLiteral where RawValue: ExpressibleByBooleanLiteral, Transformer == IdentityTransformer<RawValue> {
+	public typealias BooleanLiteralType = RawValue.BooleanLiteralType
+
+	public init(booleanLiteral value: BooleanLiteralType) {
+		self.init(value: RawValue(booleanLiteral: value))
+	}
+}
+
+extension TransformedAttribute: ExpressibleByIntegerLiteral where RawValue: ExpressibleByIntegerLiteral, Transformer == IdentityTransformer<RawValue> {
+	public typealias IntegerLiteralType = RawValue.IntegerLiteralType
+
+	public init(integerLiteral value: IntegerLiteralType) {
+		self.init(value: RawValue(integerLiteral: value))
+	}
+}
+
+// regretably, array and dictionary literals are not so easy because Dictionaries and Arrays
+// cannot be turned back into variadic arguments to pass onto the RawValue type's constructor.
+
+// we can still provide a case for the Array and Dictionary types, though.
+public protocol DictionaryType {
+	associatedtype Key: Hashable
+	associatedtype Value
+
+	init<S>(_ keysAndValues: S, uniquingKeysWith combine: (Dictionary<Key, Value>.Value, Dictionary<Key, Value>.Value) throws -> Dictionary<Key, Value>.Value) rethrows where S : Sequence, S.Element == (Key, Value)
+}
+extension Dictionary: DictionaryType {}
+
+extension TransformedAttribute: ExpressibleByDictionaryLiteral where RawValue: DictionaryType, Transformer == IdentityTransformer<RawValue> {
+	public typealias Key = RawValue.Key
+
+	public typealias Value = RawValue.Value
+
+	public init(dictionaryLiteral elements: (RawValue.Key, RawValue.Value)...) {
+
+		// we arbitrarily keep the first value if two values are assigned to the same key
+		self.init(value: RawValue(elements, uniquingKeysWith: { val, _ in val }))
+	}
+}
+
+public protocol ArrayType {
+	associatedtype Element
+
+	init<S>(_ s: S) where Element == S.Element, S : Sequence
+}
+extension Array: ArrayType {}
+extension ArraySlice: ArrayType {}
+
+extension TransformedAttribute: ExpressibleByArrayLiteral where RawValue: ArrayType, Transformer == IdentityTransformer<RawValue> {
+	public typealias ArrayLiteralElement = RawValue.Element
+
+	public init(arrayLiteral elements: ArrayLiteralElement...) {
+		self.init(value: RawValue(elements))
+	}
+}

Sources/JSONAPITestLib/EntityCheck.swift

@@ -0,0 +1,84 @@
+//
+//  EntityCheck.swift
+//  JSONAPITestLib
+//
+//  Created by Mathew Polzin on 11/27/18.
+//
+
+import JSONAPI
+
+public enum EntityCheckError: Swift.Error {
+	/// The attributes should live in a struct, not
+	/// another type class.
+	case attributesNotStruct
+
+	/// The relationships should live in a struct, not
+	/// another type class.
+	case relationshipsNotStruct
+
+	/// All stored properties on an Attributes struct should
+	/// be one of the supplied Attribute types.
+	case nonAttribute(named: String)
+
+	/// All stored properties on a Relationships struct should
+	/// be one of the supplied Relationship types.
+	case nonRelationship(named: String)
+
+	/// It is explicitly stated by the JSON spec
+	/// a "none" value for arrays is an empty array, not `nil`.
+	case nullArray(named: String)
+}
+
+public struct EntityCheckErrors: Swift.Error {
+	let problems: [EntityCheckError]
+}
+
+private protocol OptionalAttributeType {}
+extension Optional: OptionalAttributeType where Wrapped: AttributeType {}
+
+private protocol OptionalArray {}
+extension Optional: OptionalArray where Wrapped: ArrayType {}
+
+private protocol AttributeTypeWithOptionalArray {}
+extension TransformedAttribute: AttributeTypeWithOptionalArray where RawValue: OptionalArray {}
+
+private protocol OptionalRelationshipType {}
+extension Optional: OptionalRelationshipType where Wrapped: RelationshipType {}
+
+public extension Entity {
+	public static func check(_ entity: Entity) throws {
+		var problems = [EntityCheckError]()
+
+		let attributesMirror = Mirror(reflecting: entity.attributes)
+
+		if attributesMirror.displayStyle != .`struct` {
+			problems.append(.attributesNotStruct)
+		}
+
+		for attribute in attributesMirror.children {
+			if attribute.value as? AttributeType == nil,
+				attribute.value as? OptionalAttributeType == nil {
+				problems.append(.nonAttribute(named: attribute.label ?? "unnamed"))
+			}
+			if attribute.value as? AttributeTypeWithOptionalArray != nil {
+				problems.append(.nullArray(named: attribute.label ?? "unnamed"))
+			}
+		}
+
+		let relationshipsMirror = Mirror(reflecting: entity.relationships)
+
+		if relationshipsMirror.displayStyle != .`struct` {
+			problems.append(.relationshipsNotStruct)
+		}
+
+		for relationship in relationshipsMirror.children {
+			if relationship.value as? RelationshipType == nil {
+				problems.append(.nonRelationship(named: relationship.label ?? "unnamed"))
+			}
+		}
+
+		guard problems.count == 0 else {
+			throw EntityCheckErrors(problems: problems)
+		}
+	}
+}