Merge pull request #30 from mattpolzin/release/1.0

Release/1.0

JSONAPI.playground/Pages/Full Client & Server Example.xcplaygroundpage/Contents.swift

@@ -4,65 +4,66 @@ import Poly
 
 // MARK: - Preamble (setup)
 
-// We make String a CreatableRawIdType. This is actually done in
+// Make String a CreatableRawIdType. This is actually done in
 // this Playground's Entities.swift file, so it is commented out here.
 /*
-var GlobalStringId: Int = 0
-extension String: CreatableRawIdType {
-	public static func unique() -> String {
-		GlobalStringId += 1
-		return String(GlobalStringId)
-	}
-}
-*/
+ var globalStringId: Int = 0
+ extension String: CreatableRawIdType {
+ public static func unique() -> String {
+ globalStringId += 1
+ return String(globalStringId)
+ }
+ }
+ */
 
-// We create a typealias given that we do not expect JSON:API Resource
+// Create a typealias because we do not expect JSON:API Resource
 // Objects for this particular API to have Metadata or Links associated
 // with them. We also expect them to have String Identifiers.
 typealias JSONEntity<Description: ResourceObjectDescription> = JSONAPI.ResourceObject<Description, NoMetadata, NoLinks, String>
 
-// Similarly, we create a typealias for unidentified entities. JSON:API
+// Similarly, create a typealias for unidentified entities. JSON:API
 // only allows unidentified entities (i.e. no "id" field) for client
 // requests that create new entities. In these situations, the server
 // is expected to assign the new entity a unique ID.
 typealias UnidentifiedJSONEntity<Description: ResourceObjectDescription> = JSONAPI.ResourceObject<Description, NoMetadata, NoLinks, Unidentified>
 
-// We create typealiases given that we do not expect JSON:API Relationships
-// for this particular API to have Metadata or Links associated
-// with them.
+// Create relationship typealiases because we do not expect
+// JSON:API Relationships for this particular API to have
+// Metadata or Links associated with them.
 typealias ToOneRelationship<Entity: Identifiable> = JSONAPI.ToOneRelationship<Entity, NoMetadata, NoLinks>
 typealias ToManyRelationship<Entity: Relatable> = JSONAPI.ToManyRelationship<Entity, NoMetadata, NoLinks>
 
-// We create a typealias for a Document given that we do not expect
+// Create a typealias for a Document because we do not expect
 // JSON:API Documents for this particular API to have Metadata, Links,
-// useful Errors, or a JSON:API Object (i.e. APIDescription).
+// useful Errors, or an APIDescription (The *SPEC* calls this
+// "API Description" the "JSON:API Object").
 typealias Document<PrimaryResourceBody: JSONAPI.ResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, UnknownJSONAPIError>
 
 // MARK: Entity Definitions
 
 enum AuthorDescription: ResourceObjectDescription {
-	public static var jsonType: String { return "authors" }
+    public static var jsonType: String { return "authors" }
 
-	public struct Attributes: JSONAPI.Attributes {
-		public let name: Attribute<String>
-	}
+    public struct Attributes: JSONAPI.Attributes {
+        public let name: Attribute<String>
+    }
 
-	public typealias Relationships = NoRelationships
+    public typealias Relationships = NoRelationships
 }
 
 typealias Author = JSONEntity<AuthorDescription>
 
 enum ArticleDescription: ResourceObjectDescription {
-	public static var jsonType: String { return "articles" }
+    public static var jsonType: String { return "articles" }
 
-	public struct Attributes: JSONAPI.Attributes {
-		public let title: Attribute<String>
-		public let abstract: Attribute<String>
-	}
+    public struct Attributes: JSONAPI.Attributes {
+        public let title: Attribute<String>
+        public let abstract: Attribute<String>
+    }
 
-	public struct Relationships: JSONAPI.Relationships {
-		public let author: ToOneRelationship<Author>
-	}
+    public struct Relationships: JSONAPI.Relationships {
+        public let author: ToOneRelationship<Author>
+    }
 }
 
 typealias Article = JSONEntity<ArticleDescription>
@@ -83,38 +84,38 @@ typealias SingleArticleDocument = Document<SingleResourceBody<Article>, NoInclud
 // that creates a document. Note that this document is the entirety
 // of a JSON:API response body.
 func articleDocument(includeAuthor: Bool) -> Either<SingleArticleDocument, SingleArticleDocumentWithIncludes> {
-	// Let's pretend all of this is coming from a database:
+    // Let's pretend all of this is coming from a database:
 
-	let authorId = Author.Identifier(rawValue: "1234")
+    let authorId = Author.Identifier(rawValue: "1234")
 
-	let article = Article(id: .init(rawValue: "5678"),
-						  attributes: .init(title: .init(value: "JSON:API in Swift"),
-											abstract: .init(value: "Not yet written")),
-						  relationships: .init(author: .init(id: authorId)),
-						  meta: .none,
-						  links: .none)
+    let article = Article(id: .init(rawValue: "5678"),
+                          attributes: .init(title: .init(value: "JSON:API in Swift"),
+                                            abstract: .init(value: "Not yet written")),
+                          relationships: .init(author: .init(id: authorId)),
+                          meta: .none,
+                          links: .none)
 
-	let document = SingleArticleDocument(apiDescription: .none,
-										 body: .init(resourceObject: article),
-										 includes: .none,
-										 meta: .none,
-										 links: .none)
+    let document = SingleArticleDocument(apiDescription: .none,
+                                         body: .init(resourceObject: article),
+                                         includes: .none,
+                                         meta: .none,
+                                         links: .none)
 
-	switch includeAuthor {
-	case false:
-		return .a(document)
+    switch includeAuthor {
+    case false:
+        return .init(document)
 
-	case true:
-		let author = Author(id: authorId,
-							attributes: .init(name: .init(value: "Janice Bluff")),
-							relationships: .none,
-							meta: .none,
-							links: .none)
+    case true:
+        let author = Author(id: authorId,
+                            attributes: .init(name: .init(value: "Janice Bluff")),
+                            relationships: .none,
+                            meta: .none,
+                            links: .none)
 
-		let includes: Includes<SingleArticleDocumentWithIncludes.Include> = .init(values: [.init(author)])
+        let includes: Includes<SingleArticleDocumentWithIncludes.Include> = .init(values: [.init(author)])
 
-		return .b(document.including(.init(values: [.init(author)])))
-	}
+        return .init(document.including(includes))
+    }
 }
 
 let encoder = JSONEncoder()
@@ -124,8 +125,8 @@ encoder.outputFormatting = .prettyPrinted
 let responseBody = articleDocument(includeAuthor: true)
 let responseData = try! encoder.encode(responseBody)
 
-// Next step would be encoding and setting as the HTTP body of a response.
-// we will just print it out instead:
+// Next step would be setting the HTTP body of a response.
+// We will just print it out instead:
 print("-----")
 print(String(data: responseData, encoding: .utf8)!)
 
@@ -139,31 +140,31 @@ print(String(data: otherResponseData, encoding: .utf8)!)
 // MARK: - Client Pseudo-example
 
 enum NetworkError: Swift.Error {
-	case serverError
-	case quantityMismatch
+    case serverError
+    case quantityMismatch
 }
 
 // Skipping over all the API stuff, here's a chunk of code that will
 // decode a document. We will assume we have made a request for a
 // single article including the author.
 func docode(articleResponseData: Data) throws -> (article: Article, author: Author) {
-	let decoder = JSONDecoder()
-	decoder.keyDecodingStrategy = .convertFromSnakeCase
+    let decoder = JSONDecoder()
+    decoder.keyDecodingStrategy = .convertFromSnakeCase
 
-	let articleDocument = try decoder.decode(SingleArticleDocumentWithIncludes.self, from: articleResponseData)
+    let articleDocument = try decoder.decode(SingleArticleDocumentWithIncludes.self, from: articleResponseData)
 
-	switch articleDocument.body {
-	case .data(let data):
-		let authors = data.includes[Author.self]
+    switch articleDocument.body {
+    case .data(let data):
+        let authors = data.includes[Author.self]
 
-		guard authors.count == 1 else {
-			throw NetworkError.quantityMismatch
-		}
+        guard authors.count == 1 else {
+            throw NetworkError.quantityMismatch
+        }
 
-		return (article: data.primary.value, author: authors[0])
-	case .errors(let errors, meta: _, links: _):
-		throw NetworkError.serverError
-	}
+        return (article: data.primary.value, author: authors[0])
+    case .errors(let errors, meta: _, links: _):
+        throw NetworkError.serverError
+    }
 }
 
 let response = try! docode(articleResponseData: responseData)

JSONAPI.playground/Pages/Sparse Fieldsets Example.xcplaygroundpage/Contents.swift

@@ -0,0 +1,72 @@
+
+import JSONAPI
+import Foundation
+
+// MARK: - Resource Object
+
+enum ThingWithPropertiesDescription: JSONAPI.ResourceObjectDescription {
+    static let jsonType: String = "thing"
+
+    //
+    // NOTE: `JSONAPI.SparsableAttributes` as opposed to `JSONAPI.Attributes`
+    //
+    struct Attributes: JSONAPI.SparsableAttributes {
+        let stringThing: Attribute<String>
+        let numberThing: Attribute<Double>
+        let boolThing: Attribute<Bool?>
+
+        //
+        // NOTE: Special implementation of `CodingKeys`
+        //
+        enum CodingKeys: String, JSONAPI.SparsableCodingKey {
+            case stringThing
+            case numberThing
+            case boolThing
+        }
+    }
+
+    typealias Relationships = NoRelationships
+}
+
+typealias ThingWithProperties = JSONAPI.ResourceObject<ThingWithPropertiesDescription, NoMetadata, NoLinks, String>
+
+// MARK: - Document
+
+//
+// NOTE: Using `JSONAPI.EncodableResourceBody` which means the document type will be `Encodable` but not `Decodable`.
+//
+typealias Document<PrimaryResourceBody: JSONAPI.EncodableResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, UnknownJSONAPIError>
+
+//
+// NOTE: Using `JSONAPI.EncodablePrimaryResource` which means the `ResourceBody` will be `Encodable` but not `Decodable.
+//
+typealias SingleDocument<T: JSONAPI.EncodablePrimaryResource> = Document<SingleResourceBody<T>, NoIncludes>
+
+// MARK: - Resource Initialization
+
+let resource = ThingWithProperties(id: .init(rawValue: "1234"),
+                                   attributes: .init(stringThing: .init(value: "hello world"),
+                                                     numberThing: .init(value: 10),
+                                                     boolThing: .init(value: nil)),
+                                   relationships: .none,
+                                   meta: .none,
+                                   links: .none)
+//
+// NOTE: Creating a sparse resource that will only encode
+//       the attribute named "stringThing"
+//
+let sparseResource = resource.sparse(with: [.stringThing])
+
+// MARK: - Encoding
+
+let encoder = JSONEncoder()
+
+let sparseResourceDoc = SingleDocument(apiDescription: .none,
+                                       body: .init(resourceObject: sparseResource),
+                                       includes: .none,
+                                       meta: .none,
+                                       links: .none)
+
+let data = try! encoder.encode(sparseResourceDoc)
+
+print(String(data: data, encoding: .utf8)!)

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

@@ -8,6 +8,7 @@ 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)
 
@@ -15,17 +16,20 @@ let singleDogDocument = SingleDogDocument(apiDescription: .none, body: .init(res
 
 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.primaryResource?.value
 let dogOwner: Person.Identifier? = dogFromData.flatMap { $0 ~> \.owner }
 
-// MARKL - Parse a request or response body with one Dog in it using an alternative model
+
+// MARK: - Parse a request or response body with one Dog in it using an alternative model
 typealias AltSingleDogDocument = JSONAPI.Document<SingleResourceBody<AlternativeDog>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>
 let altDogResponse = try! JSONDecoder().decode(AltSingleDogDocument.self, from: singleDogData)
 let altDogFromData = altDogResponse.body.primaryResource?.value
 let altDogHuman: Person.Identifier? = altDogFromData.flatMap { $0 ~> \.human }
 
+
 // MARK: - Create a request or response with multiple people and dogs and houses included
 let personIds = [Person.Identifier(), Person.Identifier()]
 let dogs = try! [Dog(name: "Buddy", owner: personIds[0]), Dog(name: "Joy", owner: personIds[0]), Dog(name: "Travis", owner: personIds[1])]
@@ -36,6 +40,7 @@ let includes = dogs.map { BatchPeopleDocument.Include($0) } + houses.map { Batch
 let batchPeopleDocument = BatchPeopleDocument(apiDescription: .none, body: .init(resourceObjects: people), includes: .init(values: includes), meta: .none, links: .none)
 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)
@@ -47,6 +52,7 @@ print("-----")
 print(peopleResponse)
 print("-----")
 
+
 // MARK: - Pass successfully parsed body to other parts of the code
 
 /*
@@ -59,6 +65,7 @@ if case let .data(bodyData) = peopleResponse.body {
 }
  */
 
+
 // MARK: - Work in the abstract
 
 func process<T: JSONAPIDocument>(document: T) {

JSONAPI.playground/contents.xcplayground

@@ -5,5 +5,6 @@
         <page name='Usage'/>
         <page name='Full Client &amp; Server Example'/>
         <page name='Full Document Verbose Generation'/>
+        <page name='Sparse Fieldsets Example'/>
     </pages>
 </playground>

JSONAPI.podspec

@@ -16,7 +16,7 @@ Pod::Spec.new do |spec|
   #
 
   spec.name         = "JSONAPI"
-  spec.version      = "0.30.0"
+  spec.version      = "1.0.0"
   spec.summary      = "Swift Codable JSON API framework."
 
   # This description is used to generate tags and improve search results.
@@ -93,7 +93,7 @@ See the JSON API Spec here: https://jsonapi.org/format/
   #  Not including the public_header_files will make all headers public.
   #
 
-  spec.source_files  = "Sources", "Sources/**/*.{swift}"
+  spec.source_files  = "Sources/JSONAPI/**/*.{swift}"
   # spec.exclude_files = "Classes/Exclude"
 
   # spec.public_header_files = "Classes/**/*.h"
@@ -119,7 +119,6 @@ See the JSON API Spec here: https://jsonapi.org/format/
   #  the lib prefix of their name.
   #
 
-  spec.framework  = "Poly"
   # spec.frameworks = "SomeFramework", "AnotherFramework"
 
   # spec.library   = "iconv"

Package.resolved

@@ -6,8 +6,8 @@
         "repositoryURL": "https://github.com/mattpolzin/Poly.git",
         "state": {
           "branch": null,
-          "revision": "d24d4c1214dd05f89eb1182a46592856dd0a0645",
-          "version": "2.0.0"
+          "revision": "38051821d7ef49e590e26e819a2fe447e50be9ff",
+          "version": "2.0.1"
         }
       }
     ]

Package.swift

@@ -18,7 +18,7 @@ let package = Package(
 			targets: ["JSONAPITesting"])
     ],
     dependencies: [
-		.package(url: "https://github.com/mattpolzin/Poly.git", from: "2.0.0"),
+		.package(url: "https://github.com/mattpolzin/Poly.git", .upToNextMajor(from: "2.0.0")),
     ],
     targets: [
         .target(

Sources/JSONAPI/Document/Document.swift

@@ -7,19 +7,26 @@
 
 import Poly
 
-public protocol JSONAPIDocument: Codable, Equatable {
-	associatedtype PrimaryResourceBody: JSONAPI.ResourceBody
-	associatedtype MetaType: JSONAPI.Meta
-	associatedtype LinksType: JSONAPI.Links
-	associatedtype IncludeType: JSONAPI.Include
-	associatedtype APIDescription: APIDescriptionType
-	associatedtype Error: JSONAPIError
+/// An `EncodableJSONAPIDocument` supports encoding but not decoding.
+/// It is actually more restrictive than `JSONAPIDocument` which supports both
+/// encoding and decoding.
+public protocol EncodableJSONAPIDocument: Equatable, Encodable {
+    associatedtype PrimaryResourceBody: JSONAPI.EncodableResourceBody
+    associatedtype MetaType: JSONAPI.Meta
+    associatedtype LinksType: JSONAPI.Links
+    associatedtype IncludeType: JSONAPI.Include
+    associatedtype APIDescription: APIDescriptionType
+    associatedtype Error: JSONAPIError
 
-	typealias Body = Document<PrimaryResourceBody, MetaType, LinksType, IncludeType, APIDescription, Error>.Body
+    typealias Body = Document<PrimaryResourceBody, MetaType, LinksType, IncludeType, APIDescription, Error>.Body
 
-	var body: Body { get }
+    var body: Body { get }
 }
 
+/// A `JSONAPIDocument` supports encoding and decoding of a JSON:API
+/// compliant Document.
+public protocol JSONAPIDocument: EncodableJSONAPIDocument, Decodable where PrimaryResourceBody: JSONAPI.ResourceBody, IncludeType: Decodable {}
+
 /// A JSON API Document represents the entire body
 /// of a JSON API request or the entire body of
 /// a JSON API response.
@@ -27,7 +34,7 @@ public protocol JSONAPIDocument: Codable, Equatable {
 /// API uses snake case, you will want to use
 /// a conversion such as the one offerred by the
 /// Foundation JSONEncoder/Decoder: `KeyDecodingStrategy`
-public struct Document<PrimaryResourceBody: JSONAPI.ResourceBody, MetaType: JSONAPI.Meta, LinksType: JSONAPI.Links, IncludeType: JSONAPI.Include, APIDescription: APIDescriptionType, Error: JSONAPIError>: JSONAPIDocument {
+public struct Document<PrimaryResourceBody: JSONAPI.EncodableResourceBody, MetaType: JSONAPI.Meta, LinksType: JSONAPI.Links, IncludeType: JSONAPI.Include, APIDescription: APIDescriptionType, Error: JSONAPIError>: EncodableJSONAPIDocument {
 	public typealias Include = IncludeType
 
 	/// The JSON API Spec calls this the JSON:API Object. It contains version
@@ -46,7 +53,9 @@ public struct Document<PrimaryResourceBody: JSONAPI.ResourceBody, MetaType: JSON
 		case data(Data)
 
 		public struct Data: Equatable {
+            /// The document's Primary Resource object(s)
 			public let primary: PrimaryResourceBody
+            /// The document's included objects
 			public let includes: Includes<Include>
 			public let meta: MetaType
 			public let links: LinksType
@@ -59,6 +68,8 @@ public struct Document<PrimaryResourceBody: JSONAPI.ResourceBody, MetaType: JSON
 			}
 		}
 
+        /// `true` if the document represents one or more errors. `false` if the
+        /// document represents JSON:API data and/or metadata.
 		public var isError: Bool {
 			guard case .errors = self else { return false }
 			return true
@@ -196,7 +207,7 @@ extension Document where IncludeType == NoIncludes, MetaType == NoMetadata, Link
 }
 */
 
-extension Document.Body.Data where PrimaryResourceBody: AppendableResourceBody {
+extension Document.Body.Data where PrimaryResourceBody: Appendable {
 	public func merging(_ other: Document.Body.Data,
 						combiningMetaWith metaMerge: (MetaType, MetaType) -> MetaType,
 						combiningLinksWith linksMerge: (LinksType, LinksType) -> LinksType) -> Document.Body.Data {
@@ -207,7 +218,7 @@ extension Document.Body.Data where PrimaryResourceBody: AppendableResourceBody {
 	}
 }
 
-extension Document.Body.Data where PrimaryResourceBody: AppendableResourceBody, MetaType == NoMetadata, LinksType == NoLinks {
+extension Document.Body.Data where PrimaryResourceBody: Appendable, MetaType == NoMetadata, LinksType == NoLinks {
 	public func merging(_ other: Document.Body.Data) -> Document.Body.Data {
 		return merging(other,
 					   combiningMetaWith: { _, _ in .none },
@@ -273,66 +284,6 @@ extension Document {
 		case links
 		case jsonapi
 	}
-	
-	public init(from decoder: Decoder) throws {
-		let container = try decoder.container(keyedBy: RootCodingKeys.self)
-
-		if let noData = NoAPIDescription() as? APIDescription {
-			apiDescription = noData
-		} else {
-			apiDescription = try container.decode(APIDescription.self, forKey: .jsonapi)
-		}
-
-		let errors = try container.decodeIfPresent([Error].self, forKey: .errors)
-
-		let meta: MetaType?
-		if let noMeta = NoMetadata() as? MetaType {
-			meta = noMeta
-		} else {
-			do {
-				meta = try container.decode(MetaType.self, forKey: .meta)
-			} catch {
-				meta = nil
-			}
-		}
-
-		let links: LinksType?
-		if let noLinks = NoLinks() as? LinksType {
-			links = noLinks
-		} else {
-			do {
-				links = try container.decode(LinksType.self, forKey: .links)
-			} catch {
-				links = nil
-			}
-		}
-
-		// If there are errors, there cannot be a body. Return errors and any metadata found.
-		if let errors = errors {
-			body = .errors(errors, meta: meta, links: links)
-			return
-		}
-
-		let data: PrimaryResourceBody
-		if let noData = NoResourceBody() as? PrimaryResourceBody {
-			data = noData
-		} else {
-			data = try container.decode(PrimaryResourceBody.self, forKey: .data)
-		}
-
-		let maybeIncludes = try container.decodeIfPresent(Includes<Include>.self, forKey: .included)
-		
-		// TODO come back to this and make robust
-
-		guard let metaVal = meta else {
-			throw JSONAPIEncodingError.missingOrMalformedMetadata
-		}
-		guard let linksVal = links else {
-			throw JSONAPIEncodingError.missingOrMalformedLinks
-		}
-		
-		body = .data(.init(primary: data, includes: maybeIncludes ?? Includes<Include>.none, meta: metaVal, links: linksVal))
-	}
 
 	public func encode(to encoder: Encoder) throws {
 		var container = encoder.container(keyedBy: RootCodingKeys.self)
@@ -377,6 +328,68 @@ extension Document {
 	}
 }
 
+extension Document: Decodable, JSONAPIDocument where PrimaryResourceBody: ResourceBody, IncludeType: Decodable {
+    public init(from decoder: Decoder) throws {
+        let container = try decoder.container(keyedBy: RootCodingKeys.self)
+
+        if let noData = NoAPIDescription() as? APIDescription {
+            apiDescription = noData
+        } else {
+            apiDescription = try container.decode(APIDescription.self, forKey: .jsonapi)
+        }
+
+        let errors = try container.decodeIfPresent([Error].self, forKey: .errors)
+
+        let meta: MetaType?
+        if let noMeta = NoMetadata() as? MetaType {
+            meta = noMeta
+        } else {
+            do {
+                meta = try container.decode(MetaType.self, forKey: .meta)
+            } catch {
+                meta = nil
+            }
+        }
+
+        let links: LinksType?
+        if let noLinks = NoLinks() as? LinksType {
+            links = noLinks
+        } else {
+            do {
+                links = try container.decode(LinksType.self, forKey: .links)
+            } catch {
+                links = nil
+            }
+        }
+
+        // If there are errors, there cannot be a body. Return errors and any metadata found.
+        if let errors = errors {
+            body = .errors(errors, meta: meta, links: links)
+            return
+        }
+
+        let data: PrimaryResourceBody
+        if let noData = NoResourceBody() as? PrimaryResourceBody {
+            data = noData
+        } else {
+            data = try container.decode(PrimaryResourceBody.self, forKey: .data)
+        }
+
+        let maybeIncludes = try container.decodeIfPresent(Includes<Include>.self, forKey: .included)
+
+        // TODO come back to this and make robust
+
+        guard let metaVal = meta else {
+            throw JSONAPIEncodingError.missingOrMalformedMetadata
+        }
+        guard let linksVal = links else {
+            throw JSONAPIEncodingError.missingOrMalformedLinks
+        }
+
+        body = .data(.init(primary: data, includes: maybeIncludes ?? Includes<Include>.none, meta: metaVal, links: linksVal))
+    }
+}
+
 // MARK: - CustomStringConvertible
 
 extension Document: CustomStringConvertible {

Sources/JSONAPI/Document/Error.swift

@@ -9,6 +9,9 @@ public protocol JSONAPIError: Swift.Error, Equatable, Codable {
 	static var unknown: Self { get }
 }
 
+/// `UnknownJSONAPIError` can actually be used in any sitaution
+/// where you don't know what errors are possible _or_ you just don't
+/// care what errors might show up.
 public enum UnknownJSONAPIError: JSONAPIError {
 	case unknownError
 	

Sources/JSONAPI/Document/Includes.swift

@@ -7,9 +7,19 @@
 
 import Poly
 
-public typealias Include = JSONPoly
+public typealias Include = EncodableJSONPoly
 
-public struct Includes<I: Include>: Codable, Equatable {
+/// A structure holding zero or more included Resource Objects.
+/// The resources are accessed by their type using a subscript.
+///
+/// If you have
+///
+/// `let includes: Includes<Include2<Thing1, Thing2>> = ...`
+///
+/// then you can access all `Thing1` included resources with
+///
+/// `let includedThings = includes[Thing1.self]`
+public struct Includes<I: Include>: Encodable, Equatable {
 	public static var none: Includes { return .init(values: []) }
 	
 	let values: [I]
@@ -17,23 +27,6 @@ public struct Includes<I: Include>: Codable, Equatable {
 	public init(values: [I]) {
 		self.values = values
 	}
-	
-	public init(from decoder: Decoder) throws {
-		var container = try decoder.unkeyedContainer()
-		
-		// If not parsing includes, no need to loop over them.
-		guard I.self != NoIncludes.self else {
-			values = []
-			return
-		}
-		
-		var valueAggregator = [I]()
-		while !container.isAtEnd {
-			valueAggregator.append(try container.decode(I.self))
-		}
-		
-		values = valueAggregator
-	}
 
 	public func encode(to encoder: Encoder) throws {
 		var container = encoder.unkeyedContainer()
@@ -52,6 +45,25 @@ public struct Includes<I: Include>: Codable, Equatable {
 	}
 }
 
+extension Includes: Decodable where I: Decodable {
+    public init(from decoder: Decoder) throws {
+        var container = try decoder.unkeyedContainer()
+
+        // If not parsing includes, no need to loop over them.
+        guard I.self != NoIncludes.self else {
+            values = []
+            return
+        }
+
+        var valueAggregator = [I]()
+        while !container.isAtEnd {
+            valueAggregator.append(try container.decode(I.self))
+        }
+
+        values = valueAggregator
+    }
+}
+
 extension Includes {
 	public func appending(_ other: Includes<I>) -> Includes {
 		return Includes(values: values + other.values)

Sources/JSONAPI/Document/ResourceBody.swift

@@ -5,29 +5,53 @@
 //  Created by Mathew Polzin on 11/10/18.
 //
 
-public protocol MaybePrimaryResource: Equatable, Codable {}
+/// This protocol allows for a `SingleResourceBody` to contain a `null`
+/// data object where `ManyResourceBody` cannot (because an empty
+/// array should be used for no results).
+public protocol OptionalEncodablePrimaryResource: Equatable, Encodable {}
 
-/// A PrimaryResource is a type that can be used in the body of a JSON API
+/// An `EncodablePrimaryResource` is a `PrimaryResource` that only supports encoding.
+/// This is actually more restrictave than `PrimaryResource`, which supports both encoding and
+/// decoding.
+public protocol EncodablePrimaryResource: OptionalEncodablePrimaryResource {}
+
+/// This protocol allows for `SingleResourceBody` to contain a `null`
+/// data object where `ManyResourceBody` cannot (because an empty
+/// array should be used for no results).
+public protocol OptionalPrimaryResource: OptionalEncodablePrimaryResource, Decodable {}
+
+/// A `PrimaryResource` is a type that can be used in the body of a JSON API
 /// document as the primary resource.
-public protocol PrimaryResource: MaybePrimaryResource {}
+public protocol PrimaryResource: EncodablePrimaryResource, OptionalPrimaryResource {}
 
-extension Optional: MaybePrimaryResource where Wrapped: PrimaryResource {}
+extension Optional: OptionalEncodablePrimaryResource where Wrapped: EncodablePrimaryResource {}
+
+extension Optional: OptionalPrimaryResource where Wrapped: PrimaryResource {}
+
+/// An `EncodableResourceBody` is a `ResourceBody` that only supports being
+/// encoded. It is actually weaker than `ResourceBody`, which supports both encoding
+/// and decoding.
+public protocol EncodableResourceBody: Equatable, Encodable {}
 
 /// A ResourceBody is a representation of the body of the JSON API Document.
 /// It can either be one resource (which can be specified as optional or not)
 /// or it can contain many resources (and array with zero or more entries).
-public protocol ResourceBody: Codable, Equatable {
-}
+public protocol ResourceBody: Decodable, EncodableResourceBody {}
 
-public protocol AppendableResourceBody: ResourceBody {
+/// A `ResourceBody` that has the ability to take on more primary
+/// resources by appending another similarly typed `ResourceBody`.
+public protocol Appendable {
 	func appending(_ other: Self) -> Self
 }
 
-public func +<R: AppendableResourceBody>(_ left: R, right: R) -> R {
+public func +<R: Appendable>(_ left: R, right: R) -> R {
 	return left.appending(right)
 }
 
-public struct SingleResourceBody<Entity: JSONAPI.MaybePrimaryResource>: ResourceBody {
+/// A type allowing for a document body containing 1 primary resource.
+/// If the `Entity` specialization is an `Optional` type, the body can contain
+/// 0 or 1 primary resources.
+public struct SingleResourceBody<Entity: JSONAPI.OptionalEncodablePrimaryResource>: EncodableResourceBody {
 	public let value: Entity
 
 	public init(resourceObject: Entity) {
@@ -35,7 +59,8 @@ public struct SingleResourceBody<Entity: JSONAPI.MaybePrimaryResource>: Resource
 	}
 }
 
-public struct ManyResourceBody<Entity: JSONAPI.PrimaryResource>: AppendableResourceBody {
+/// A type allowing for a document body containing 0 or more primary resources.
+public struct ManyResourceBody<Entity: JSONAPI.EncodablePrimaryResource>: EncodableResourceBody, Appendable {
 	public let values: [Entity]
 
 	public init(resourceObjects: [Entity]) {
@@ -55,41 +80,36 @@ public struct NoResourceBody: ResourceBody {
 
 // MARK: Codable
 extension SingleResourceBody {
-	public init(from decoder: Decoder) throws {
-		let container = try decoder.singleValueContainer()
-
-		let anyNil: Any? = nil
-		if container.decodeNil(),
-			let val = anyNil as? Entity {
-			value = val
-			return
-		}
-
-		value = try container.decode(Entity.self)
-	}
-
 	public func encode(to encoder: Encoder) throws {
 		var container = encoder.singleValueContainer()
 
-		if (value as Any?) == nil {
-			try container.encodeNil()
-			return
-		}
+        let anyNil: Any? = nil
+        let nilValue = anyNil as? Entity
+        guard value != nilValue else {
+            try container.encodeNil()
+            return
+        }
 
 		try container.encode(value)
 	}
 }
 
-extension ManyResourceBody {
-	public init(from decoder: Decoder) throws {
-		var container = try decoder.unkeyedContainer()
-		var valueAggregator = [Entity]()
-		while !container.isAtEnd {
-			valueAggregator.append(try container.decode(Entity.self))
-		}
-		values = valueAggregator
-	}
+extension SingleResourceBody: Decodable, ResourceBody where Entity: OptionalPrimaryResource {
+    public init(from decoder: Decoder) throws {
+        let container = try decoder.singleValueContainer()
 
+        let anyNil: Any? = nil
+        if container.decodeNil(),
+            let val = anyNil as? Entity {
+            value = val
+            return
+        }
+
+        value = try container.decode(Entity.self)
+    }
+}
+
+extension ManyResourceBody {
 	public func encode(to encoder: Encoder) throws {
 		var container = encoder.unkeyedContainer()
 
@@ -99,6 +119,17 @@ extension ManyResourceBody {
 	}
 }
 
+extension ManyResourceBody: Decodable, ResourceBody where Entity: PrimaryResource {
+    public init(from decoder: Decoder) throws {
+        var container = try decoder.unkeyedContainer()
+        var valueAggregator = [Entity]()
+        while !container.isAtEnd {
+            valueAggregator.append(try container.decode(Entity.self))
+        }
+        values = valueAggregator
+    }
+}
+
 // MARK: CustomStringConvertible
 
 extension SingleResourceBody: CustomStringConvertible {

Sources/JSONAPI/EmptyObjectDecoder.swift

@@ -0,0 +1,215 @@
+//
+//  EmptyObjectDecoder.swift
+//  JSONAPI
+//
+//  Created by Mathew Polzin on 7/2/19.
+//
+
+/// `EmptyObjectDecoder` exists internally for the sole purpose of
+/// allowing certain fallback logic paths to attempt to create `Decodable`
+/// types from empty containers (specifically in a way that is agnostic
+/// of any given encoding). In other words, this serves the same purpose
+/// as `JSONDecoder().decode(Thing.self, from: "{}".data(using: .utf8)!)`
+/// without needing to use a third party or `Foundation` library decoder.
+struct EmptyObjectDecoder: Decoder {
+
+    var codingPath: [CodingKey] = []
+
+    var userInfo: [CodingUserInfoKey : Any] = [:]
+
+    func container<Key>(keyedBy type: Key.Type) throws -> KeyedDecodingContainer<Key> where Key : CodingKey {
+        return KeyedDecodingContainer(EmptyKeyedContainer())
+    }
+
+    func unkeyedContainer() throws -> UnkeyedDecodingContainer {
+        return EmptyUnkeyedContainer()
+    }
+
+    func singleValueContainer() throws -> SingleValueDecodingContainer {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeSingleValue
+    }
+}
+
+enum EmptyObjectDecodingError: Swift.Error {
+    case emptyObjectCannotBeSingleValue
+    case emptyObjectCannotBeUnkeyedValues
+    case emptyObjectCannotHaveKeyedValues
+    case emptyObjectCannotHaveNestedContainers
+    case emptyObjectCannotHaveSuper
+}
+
+struct EmptyUnkeyedContainer: UnkeyedDecodingContainer {
+    var codingPath: [CodingKey] { return [] }
+
+    var count: Int? { return 0 }
+
+    var isAtEnd: Bool { return true }
+
+    var currentIndex: Int { return 0 }
+
+    mutating func decodeNil() throws -> Bool {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Bool.Type) throws -> Bool {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: String.Type) throws -> String {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Double.Type) throws -> Double {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Float.Type) throws -> Float {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Int.Type) throws -> Int {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Int8.Type) throws -> Int8 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Int16.Type) throws -> Int16 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Int32.Type) throws -> Int32 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Int64.Type) throws -> Int64 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: UInt.Type) throws -> UInt {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: UInt8.Type) throws -> UInt8 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: UInt16.Type) throws -> UInt16 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: UInt32.Type) throws -> UInt32 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: UInt64.Type) throws -> UInt64 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode<T>(_ type: T.Type) throws -> T where T : Decodable {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func nestedContainer<NestedKey>(keyedBy type: NestedKey.Type) throws -> KeyedDecodingContainer<NestedKey> where NestedKey : CodingKey {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveNestedContainers
+    }
+
+    mutating func nestedUnkeyedContainer() throws -> UnkeyedDecodingContainer {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveNestedContainers
+    }
+
+    mutating func superDecoder() throws -> Decoder {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveSuper
+    }
+}
+
+struct EmptyKeyedContainer<Key: CodingKey>: KeyedDecodingContainerProtocol {
+    var codingPath: [CodingKey] { return [] }
+
+    var allKeys: [Key] { return [] }
+
+    func contains(_ key: Key) -> Bool {
+        return false
+    }
+
+    func decodeNil(forKey key: Key) throws -> Bool {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Bool.Type, forKey key: Key) throws -> Bool {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: String.Type, forKey key: Key) throws -> String {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Double.Type, forKey key: Key) throws -> Double {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Float.Type, forKey key: Key) throws -> Float {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Int.Type, forKey key: Key) throws -> Int {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Int8.Type, forKey key: Key) throws -> Int8 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Int16.Type, forKey key: Key) throws -> Int16 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Int32.Type, forKey key: Key) throws -> Int32 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Int64.Type, forKey key: Key) throws -> Int64 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: UInt.Type, forKey key: Key) throws -> UInt {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: UInt8.Type, forKey key: Key) throws -> UInt8 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: UInt16.Type, forKey key: Key) throws -> UInt16 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: UInt32.Type, forKey key: Key) throws -> UInt32 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: UInt64.Type, forKey key: Key) throws -> UInt64 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode<T>(_ type: T.Type, forKey key: Key) throws -> T where T : Decodable {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func nestedContainer<NestedKey>(keyedBy type: NestedKey.Type, forKey key: Key) throws -> KeyedDecodingContainer<NestedKey> where NestedKey : CodingKey {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveNestedContainers
+    }
+
+    func nestedUnkeyedContainer(forKey key: Key) throws -> UnkeyedDecodingContainer {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveNestedContainers
+    }
+
+    func superDecoder() throws -> Decoder {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveSuper
+    }
+
+    func superDecoder(forKey key: Key) throws -> Decoder {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveSuper
+    }
+}

Sources/JSONAPI/Meta/Meta.swift

@@ -19,6 +19,8 @@ public protocol Meta: Codable, Equatable {
 // nullable.
 extension Optional: Meta where Wrapped: Meta {}
 
+/// Use this type when you want to specify not to encode or decode any metadata
+/// for a type.
 public struct NoMetadata: Meta, CustomStringConvertible {
 	public static var none: NoMetadata { return NoMetadata() }
 

Sources/JSONAPI/Resource/Id.swift

@@ -28,6 +28,9 @@ public protocol CreatableRawIdType: RawIdType {
 
 extension String: RawIdType {}
 
+/// A type that can be used as the `MaybeRawId` for a `ResourceObject` that does not
+/// have an Id (most likely because it was created by a client and the server will be responsible
+/// for assigning it an Id).
 public struct Unidentified: MaybeRawId, CustomStringConvertible {
 	public init() {}
 	

Sources/JSONAPI/Resource/Poly+PrimaryResource.swift

@@ -15,9 +15,10 @@ import Poly
 /// disparate types under one roof for
 /// the purposes of JSON API compliant
 /// encoding or decoding.
-public typealias JSONPoly = Poly & PrimaryResource
+public typealias EncodableJSONPoly = Poly & EncodablePrimaryResource
 
-public typealias PolyWrapped = Codable & Equatable
+public typealias EncodablePolyWrapped = Encodable & Equatable
+public typealias PolyWrapped = EncodablePolyWrapped & Decodable
 
 extension Poly0: PrimaryResource {
 	public init(from decoder: Decoder) throws {
@@ -30,28 +31,46 @@ extension Poly0: PrimaryResource {
 }
 
 // MARK: - 1 type
-extension Poly1: PrimaryResource, MaybePrimaryResource where A: PolyWrapped {}
+extension Poly1: EncodablePrimaryResource, OptionalEncodablePrimaryResource where A: EncodablePolyWrapped {}
+
+extension Poly1: PrimaryResource, OptionalPrimaryResource where A: PolyWrapped {}
 
 // MARK: - 2 types
-extension Poly2: PrimaryResource, MaybePrimaryResource where A: PolyWrapped, B: PolyWrapped {}
+extension Poly2: EncodablePrimaryResource, OptionalEncodablePrimaryResource where A: EncodablePolyWrapped, B: EncodablePolyWrapped {}
+
+extension Poly2: PrimaryResource, OptionalPrimaryResource where A: PolyWrapped, B: PolyWrapped {}
 
 // MARK: - 3 types
-extension Poly3: PrimaryResource, MaybePrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped {}
+extension Poly3: EncodablePrimaryResource, OptionalEncodablePrimaryResource where A: EncodablePolyWrapped, B: EncodablePolyWrapped, C: EncodablePolyWrapped {}
+
+extension Poly3: PrimaryResource, OptionalPrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped {}
 
 // MARK: - 4 types
-extension Poly4: PrimaryResource, MaybePrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped {}
+extension Poly4: EncodablePrimaryResource, OptionalEncodablePrimaryResource where A: EncodablePolyWrapped, B: EncodablePolyWrapped, C: EncodablePolyWrapped, D: EncodablePolyWrapped {}
+
+extension Poly4: PrimaryResource, OptionalPrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped {}
 
 // MARK: - 5 types
-extension Poly5: PrimaryResource, MaybePrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped, E: PolyWrapped {}
+extension Poly5: EncodablePrimaryResource, OptionalEncodablePrimaryResource where A: EncodablePolyWrapped, B: EncodablePolyWrapped, C: EncodablePolyWrapped, D: EncodablePolyWrapped, E: EncodablePolyWrapped {}
+
+extension Poly5: PrimaryResource, OptionalPrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped, E: PolyWrapped {}
 
 // MARK: - 6 types
-extension Poly6: PrimaryResource, MaybePrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped, E: PolyWrapped, F: PolyWrapped {}
+extension Poly6: EncodablePrimaryResource, OptionalEncodablePrimaryResource where A: EncodablePolyWrapped, B: EncodablePolyWrapped, C: EncodablePolyWrapped, D: EncodablePolyWrapped, E: EncodablePolyWrapped, F: EncodablePolyWrapped {}
+
+extension Poly6: PrimaryResource, OptionalPrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped, E: PolyWrapped, F: PolyWrapped {}
 
 // MARK: - 7 types
-extension Poly7: PrimaryResource, MaybePrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped, E: PolyWrapped, F: PolyWrapped, G: PolyWrapped {}
+extension Poly7: EncodablePrimaryResource, OptionalEncodablePrimaryResource where A: EncodablePolyWrapped, B: EncodablePolyWrapped, C: EncodablePolyWrapped, D: EncodablePolyWrapped, E: EncodablePolyWrapped, F: EncodablePolyWrapped, G: EncodablePolyWrapped {}
+
+extension Poly7: PrimaryResource, OptionalPrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped, E: PolyWrapped, F: PolyWrapped, G: PolyWrapped {}
 
 // MARK: - 8 types
-extension Poly8: PrimaryResource, MaybePrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped, E: PolyWrapped, F: PolyWrapped, G: PolyWrapped, H: PolyWrapped {}
+extension Poly8: EncodablePrimaryResource, OptionalEncodablePrimaryResource where A: EncodablePolyWrapped, B: EncodablePolyWrapped, C: EncodablePolyWrapped, D: EncodablePolyWrapped, E: EncodablePolyWrapped, F: EncodablePolyWrapped, G: EncodablePolyWrapped, H: EncodablePolyWrapped {}
+
+extension Poly8: PrimaryResource, OptionalPrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped, E: PolyWrapped, F: PolyWrapped, G: PolyWrapped, H: PolyWrapped {}
 
 // MARK: - 9 types
-extension Poly9: PrimaryResource, MaybePrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped, E: PolyWrapped, F: PolyWrapped, G: PolyWrapped, H: PolyWrapped, I: PolyWrapped {}
+extension Poly9: EncodablePrimaryResource, OptionalEncodablePrimaryResource where A: EncodablePolyWrapped, B: EncodablePolyWrapped, C: EncodablePolyWrapped, D: EncodablePolyWrapped, E: EncodablePolyWrapped, F: EncodablePolyWrapped, G: EncodablePolyWrapped, H: EncodablePolyWrapped, I: EncodablePolyWrapped {}
+
+extension Poly9: PrimaryResource, OptionalPrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped, E: PolyWrapped, F: PolyWrapped, G: PolyWrapped, H: PolyWrapped, I: PolyWrapped {}

Sources/JSONAPI/Resource/Relationship.swift

@@ -190,10 +190,6 @@ extension ToOneRelationship: Codable where Identifiable.Identifier: OptionalId {
 	public func encode(to encoder: Encoder) throws {
 		var container = encoder.container(keyedBy: ResourceLinkageCodingKeys.self)
 
-		if (id as Any?) == nil {
-			try container.encodeNil(forKey: .data)
-		}
-
 		if MetaType.self != NoMetadata.self {
 			try container.encode(meta, forKey: .meta)
 		}

Sources/JSONAPI/Resource/ResourceObject.swift

@@ -5,6 +5,7 @@
 //  Created by Mathew Polzin on 7/24/18.
 //
 
+
 /// A JSON API structure within an ResourceObject that contains
 /// named properties of types `ToOneRelationship` and
 /// `ToManyRelationship`.
@@ -14,6 +15,16 @@ public protocol Relationships: Codable & Equatable {}
 /// properties of any types that are JSON encodable.
 public protocol Attributes: Codable & Equatable {}
 
+/// CodingKeys must be `CodingKey` and `Equatable` in order
+/// to support Sparse Fieldsets.
+public typealias SparsableCodingKey = CodingKey & Equatable
+
+/// Attributes containing publicly accessible and `Equatable`
+/// CodingKeys are required to support Sparse Fieldsets.
+public protocol SparsableAttributes: Attributes {
+    associatedtype CodingKeys: SparsableCodingKey
+}
+
 /// Can be used as `Relationships` Type for Entities that do not
 /// have any Relationships.
 public struct NoRelationships: Relationships {
@@ -47,7 +58,7 @@ public protocol ResourceObjectProxyDescription: JSONTyped {
 	associatedtype Relationships: Equatable
 }
 
-/// An `ResourceObjectDescription` describes a JSON API
+/// A `ResourceObjectDescription` describes a JSON API
 /// Resource Object. The Resource Object
 /// itself is encoded and decoded as an
 /// `ResourceObject`, which gets specialized on an
@@ -394,14 +405,14 @@ extension ResourceObject where MetaType == NoMetadata, LinksType == NoLinks, Ent
 // MARK: Pointer for Relationships use.
 public extension ResourceObject where EntityRawIdType: JSONAPI.RawIdType {
 
-	/// An ResourceObject.Pointer is a `ToOneRelationship` with no metadata or links.
-	/// This is just a convenient way to reference an ResourceObject so that
-	/// other Entities' Relationships can be built up from it.
+	/// A `ResourceObject.Pointer` is a `ToOneRelationship` with no metadata or links.
+	/// This is just a convenient way to reference a `ResourceObject` so that
+	/// other ResourceObjects' Relationships can be built up from it.
 	typealias Pointer = ToOneRelationship<ResourceObject, NoMetadata, NoLinks>
 
-	/// ResourceObject.Pointers is a `ToManyRelationship` with no metadata or links.
-	/// This is just a convenient way to reference a bunch of Entities so
-	/// that other Entities' Relationships can be built up from them.
+	/// `ResourceObject.Pointers` is a `ToManyRelationship` with no metadata or links.
+	/// This is just a convenient way to reference a bunch of ResourceObjects so
+	/// that other ResourceObjects' Relationships can be built up from them.
 	typealias Pointers = ToManyRelationship<ResourceObject, NoMetadata, NoLinks>
 
 	/// Get a pointer to this resource object that can be used as a
@@ -410,6 +421,8 @@ public extension ResourceObject where EntityRawIdType: JSONAPI.RawIdType {
 		return Pointer(resourceObject: self)
 	}
 
+    /// Get a pointer (i.e. `ToOneRelationship`) to this resource
+    /// object with the given metadata and links attached.
 	func pointer<MType: JSONAPI.Meta, LType: JSONAPI.Links>(withMeta meta: MType, links: LType) -> ToOneRelationship<ResourceObject, MType, LType> {
 		return ToOneRelationship(resourceObject: self, meta: meta, links: links)
 	}
@@ -417,20 +430,20 @@ public extension ResourceObject where EntityRawIdType: JSONAPI.RawIdType {
 
 // MARK: Identifying Unidentified Entities
 public extension ResourceObject where EntityRawIdType == Unidentified {
-	/// Create a new ResourceObject from this one with a newly created
+	/// Create a new `ResourceObject` from this one with a newly created
 	/// unique Id of the given type.
 	func identified<RawIdType: CreatableRawIdType>(byType: RawIdType.Type) -> ResourceObject<Description, MetaType, LinksType, RawIdType> {
 		return .init(attributes: attributes, relationships: relationships, meta: meta, links: links)
 	}
 
-	/// Create a new ResourceObject from this one with the given Id.
+	/// Create a new `ResourceObject` from this one with the given Id.
 	func identified<RawIdType: JSONAPI.RawIdType>(by id: RawIdType) -> ResourceObject<Description, MetaType, LinksType, RawIdType> {
 		return .init(id: ResourceObject<Description, MetaType, LinksType, RawIdType>.Identifier(rawValue: id), attributes: attributes, relationships: relationships, meta: meta, links: links)
 	}
 }
 
 public extension ResourceObject where EntityRawIdType: CreatableRawIdType {
-	/// Create a copy of this ResourceObject with a new unique Id.
+	/// Create a copy of this `ResourceObject` with a new unique Id.
 	func withNewIdentifier() -> ResourceObject {
 		return ResourceObject(attributes: attributes, relationships: relationships, meta: meta, links: links)
 	}
@@ -546,61 +559,63 @@ infix operator ~>
 
 // MARK: - Codable
 private enum ResourceObjectCodingKeys: String, CodingKey {
-	case type = "type"
-	case id = "id"
-	case attributes = "attributes"
-	case relationships = "relationships"
-	case meta = "meta"
-	case links = "links"
+    case type = "type"
+    case id = "id"
+    case attributes = "attributes"
+    case relationships = "relationships"
+    case meta = "meta"
+    case links = "links"
 }
 
 public extension ResourceObject {
-	func encode(to encoder: Encoder) throws {
-		var container = encoder.container(keyedBy: ResourceObjectCodingKeys.self)
-		
-		try container.encode(ResourceObject.jsonType, forKey: .type)
-		
-		if EntityRawIdType.self != Unidentified.self {
-			try container.encode(id, forKey: .id)
-		}
-		
-		if Description.Attributes.self != NoAttributes.self {
-			try container.encode(attributes, forKey: .attributes)
-		}
-		
-		if Description.Relationships.self != NoRelationships.self {
-			try container.encode(relationships, forKey: .relationships)
-		}
+    func encode(to encoder: Encoder) throws {
+        var container = encoder.container(keyedBy: ResourceObjectCodingKeys.self)
 
-		if MetaType.self != NoMetadata.self {
-			try container.encode(meta, forKey: .meta)
-		}
+        try container.encode(ResourceObject.jsonType, forKey: .type)
 
-		if LinksType.self != NoLinks.self {
-			try container.encode(links, forKey: .links)
-		}
-	}
+        if EntityRawIdType.self != Unidentified.self {
+            try container.encode(id, forKey: .id)
+        }
 
-	init(from decoder: Decoder) throws {
-		
-		let container = try decoder.container(keyedBy: ResourceObjectCodingKeys.self)
-		
-		let type = try container.decode(String.self, forKey: .type)
-		
-		guard ResourceObject.jsonType == type else {
-			throw JSONAPIEncodingError.typeMismatch(expected: Description.jsonType, found: type)
-		}
+        if Description.Attributes.self != NoAttributes.self {
+            let nestedEncoder = container.superEncoder(forKey: .attributes)
+            try attributes.encode(to: nestedEncoder)
+        }
 
-		let maybeUnidentified = Unidentified() as? EntityRawIdType
-		id = try maybeUnidentified.map { ResourceObject.Id(rawValue: $0) } ?? container.decode(ResourceObject.Id.self, forKey: .id)
+        if Description.Relationships.self != NoRelationships.self {
+            try container.encode(relationships, forKey: .relationships)
+        }
 
-		attributes = try (NoAttributes() as? Description.Attributes) ??
-			container.decode(Description.Attributes.self, forKey: .attributes)
+        if MetaType.self != NoMetadata.self {
+            try container.encode(meta, forKey: .meta)
+        }
 
-		relationships = try (NoRelationships() as? Description.Relationships) ?? container.decode(Description.Relationships.self, forKey: .relationships)
+        if LinksType.self != NoLinks.self {
+            try container.encode(links, forKey: .links)
+        }
+    }
 
-		meta = try (NoMetadata() as? MetaType) ?? container.decode(MetaType.self, forKey: .meta)
+    init(from decoder: Decoder) throws {
+        let container = try decoder.container(keyedBy: ResourceObjectCodingKeys.self)
 
-		links = try (NoLinks() as? LinksType) ?? container.decode(LinksType.self, forKey: .links)
-	}
+        let type = try container.decode(String.self, forKey: .type)
+
+        guard ResourceObject.jsonType == type else {
+            throw JSONAPIEncodingError.typeMismatch(expected: Description.jsonType, found: type)
+        }
+
+        let maybeUnidentified = Unidentified() as? EntityRawIdType
+        id = try maybeUnidentified.map { ResourceObject.Id(rawValue: $0) } ?? container.decode(ResourceObject.Id.self, forKey: .id)
+
+        attributes = try (NoAttributes() as? Description.Attributes) ??
+            container.decode(Description.Attributes.self, forKey: .attributes)
+
+        relationships = try (NoRelationships() as? Description.Relationships)
+            ?? container.decodeIfPresent(Description.Relationships.self, forKey: .relationships)
+            ?? Description.Relationships(from: EmptyObjectDecoder())
+
+        meta = try (NoMetadata() as? MetaType) ?? container.decode(MetaType.self, forKey: .meta)
+
+        links = try (NoLinks() as? LinksType) ?? container.decode(LinksType.self, forKey: .links)
+    }
 }

Sources/JSONAPI/Resource/Transformer.swift

@@ -7,22 +7,26 @@
 
 /// A Transformer simply defines a static function that transforms a value.
 public protocol Transformer {
-	associatedtype From
-	associatedtype To
+    associatedtype From
+    associatedtype To
 
-	static func transform(_ value: From) throws -> To
+    /// Turn value of type `From` into a value of type `To` or
+    /// throw an error on failure.
+    static func transform(_ value: From) throws -> To
 }
 
 /// ReversibleTransformers define a function that reverses the transform
 /// operation.
 public protocol ReversibleTransformer: Transformer {
-	static func reverse(_ value: To) throws -> From
+    /// Turn a value of type `To` into a value of type `From` or
+    /// throw an error on failure.
+    static func reverse(_ value: To) throws -> From
 }
 
 /// The IdentityTransformer does not perform any transformation on a value.
 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 }
+    public static func transform(_ value: T) throws -> T { return value }
+    public static func reverse(_ value: T) throws -> T { return value }
 }
 
 // MARK: - Validator
@@ -37,13 +41,16 @@ 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 reverse(_ value: To) throws -> To {
+        let _ = try transform(value)
+        return value
+    }
 
-	public static func validate(_ value: To) throws -> To {
-		let _ = try transform(value)
-		return value
-	}
+    /// Validate the given value and then return it if valid.
+    /// throws an erro if invalid.
+    /// - returns: The same value passed in, if it was valid.
+    public static func validate(_ value: To) throws -> To {
+        let _ = try transform(value)
+        return value
+    }
 }

Sources/JSONAPI/SparseFields/SparseFieldEncoder.swift

@@ -0,0 +1,204 @@
+//
+//  SparseEncoder.swift
+//  
+//
+//  Created by Mathew Polzin on 8/4/19.
+//
+
+class SparseFieldEncoder<SparseKey: CodingKey & Equatable>: Encoder {
+    private let wrappedEncoder: Encoder
+    private let allowedKeys: [SparseKey]
+
+    public var codingPath: [CodingKey] {
+        return wrappedEncoder.codingPath
+    }
+
+    public var userInfo: [CodingUserInfoKey : Any] {
+        return wrappedEncoder.userInfo
+    }
+
+    public init(wrapping encoder: Encoder, encoding allowedKeys: [SparseKey]) {
+        wrappedEncoder = encoder
+        self.allowedKeys = allowedKeys
+    }
+
+    public func container<Key>(keyedBy type: Key.Type) -> KeyedEncodingContainer<Key> where Key : CodingKey {
+        let container = SparseFieldKeyedEncodingContainer(wrapping: wrappedEncoder.container(keyedBy: type),
+                                                          encoding: allowedKeys)
+        return KeyedEncodingContainer(container)
+    }
+
+    public func unkeyedContainer() -> UnkeyedEncodingContainer {
+        return wrappedEncoder.unkeyedContainer()
+    }
+
+    public func singleValueContainer() -> SingleValueEncodingContainer {
+        return wrappedEncoder.singleValueContainer()
+    }
+}
+
+struct SparseFieldKeyedEncodingContainer<Key, SparseKey>: KeyedEncodingContainerProtocol where SparseKey: CodingKey, SparseKey: Equatable, Key: CodingKey {
+    private var wrappedContainer: KeyedEncodingContainer<Key>
+    private let allowedKeys: [SparseKey]
+
+    public var codingPath: [CodingKey] {
+        return wrappedContainer.codingPath
+    }
+
+    public init(wrapping container: KeyedEncodingContainer<Key>, encoding allowedKeys: [SparseKey]) {
+        wrappedContainer = container
+        self.allowedKeys = allowedKeys
+    }
+
+    /// Ask the container whether the given key should be encoded.
+    public func shouldAllow(key: Key) -> Bool {
+        if let key = key as? SparseKey {
+            return allowedKeys.contains(key)
+        }
+        return true
+    }
+
+    public mutating func encodeNil(forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encodeNil(forKey: key)
+    }
+
+    public mutating func encode(_ value: Bool, forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func encode(_ value: String, forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func encode(_ value: Double, forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func encode(_ value: Float, forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func encode(_ value: Int, forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func encode(_ value: Int8, forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func encode(_ value: Int16, forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func encode(_ value: Int32, forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func encode(_ value: Int64, forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func encode(_ value: UInt, forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func encode(_ value: UInt8, forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func encode(_ value: UInt16, forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func encode(_ value: UInt32, forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func encode(_ value: UInt64, forKey key: Key) throws {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func encode<T>(_ value: T, forKey key: Key) throws where T : Encodable {
+        guard shouldAllow(key: key) else { return }
+
+        try wrappedContainer.encode(value, forKey: key)
+    }
+
+    public mutating func nestedContainer<NestedKey>(keyedBy keyType: NestedKey.Type,
+                                                    forKey key: Key) -> KeyedEncodingContainer<NestedKey> where NestedKey : CodingKey {
+        guard shouldAllow(key: key) else {
+            return KeyedEncodingContainer(
+                // TODO: not needed by JSONAPI library, but for completeness could
+                //      add an EmptyObjectEncoder that can be returned here so that
+                //      at least nothing gets encoded within the nested container
+                SparseFieldKeyedEncodingContainer<NestedKey, SparseKey>(wrapping: wrappedContainer.nestedContainer(keyedBy: keyType,
+                                                                                                                   forKey: key),
+                                                                        encoding: [])
+            )
+        }
+
+        return KeyedEncodingContainer(
+            SparseFieldKeyedEncodingContainer<NestedKey, SparseKey>(wrapping: wrappedContainer.nestedContainer(keyedBy: keyType,
+                                                                                                               forKey: key),
+                                                                    encoding: allowedKeys)
+        )
+    }
+
+    public mutating func nestedUnkeyedContainer(forKey key: Key) -> UnkeyedEncodingContainer {
+        guard shouldAllow(key: key) else {
+            // TODO: not needed by JSONAPI library, but for completeness could
+            //      add an EmptyObjectEncoder that can be returned here so that
+            //      at least nothing gets encoded within the nested container
+            return wrappedContainer.nestedUnkeyedContainer(forKey: key)
+        }
+
+        return wrappedContainer.nestedUnkeyedContainer(forKey: key)
+    }
+
+    public mutating func superEncoder() -> Encoder {
+        return SparseFieldEncoder(wrapping: wrappedContainer.superEncoder(),
+                                  encoding: allowedKeys)
+    }
+
+    public mutating func superEncoder(forKey key: Key) -> Encoder {
+        guard shouldAllow(key: key) else {
+            // NOTE: We are creating a sparse field encoder with no allowed keys
+            //      here because the given key should not be allowed.
+            return SparseFieldEncoder(wrapping: wrappedContainer.superEncoder(forKey: key),
+                                      encoding: [SparseKey]())
+        }
+
+        return SparseFieldEncoder(wrapping: wrappedContainer.superEncoder(forKey: key),
+                                  encoding: allowedKeys)
+    }
+}