add test coverage and fill a logic gap around nullable relationships paired with non-optional id metadata.

Author: mattpolzin

Sources/JSONAPI/Resource/Relationship.swift

@@ -133,23 +133,23 @@ public struct ToManyRelationship<Relatable: JSONAPI.Relatable, IdMetaType: JSONA
         }
     }
 
-    public let metaIds: [ID]
+    public let idsWithMeta: [ID]
 
     public var ids: [Relatable.ID] {
-        metaIds.map(\.id)
+        idsWithMeta.map(\.id)
     }
 
     public let meta: MetaType
     public let links: LinksType
 
     public init(idsWithMetadata ids: [(Relatable.ID, IdMetaType)], meta: MetaType, links: LinksType) {
-        self.metaIds = ids.map { ID.init($0) }
+        self.idsWithMeta = ids.map { ID.init($0) }
         self.meta = meta
         self.links = links
     }
 
     public init<T: JSONAPIIdentifiable>(pointers: [ToOneRelationship<T, NoIdMetadata, NoMetadata, NoLinks>], meta: MetaType, links: LinksType) where T.ID == Relatable.ID, IdMetaType == NoIdMetadata {
-        metaIds = pointers.map { .init(id: $0.id, meta: .none) }
+        idsWithMeta = pointers.map { .init(id: $0.id, meta: .none) }
         self.meta = meta
         self.links = links
     }
@@ -169,7 +169,7 @@ public struct ToManyRelationship<Relatable: JSONAPI.Relatable, IdMetaType: JSONA
 
 extension ToManyRelationship where IdMetaType == NoIdMetadata {
     public init(ids: [Relatable.ID], meta: MetaType, links: LinksType) {
-        self.metaIds = ids.map { .init(id: $0, meta: .none) }
+        self.idsWithMeta = ids.map { .init(id: $0, meta: .none) }
         self.meta = meta
         self.links = links
     }
@@ -263,6 +263,9 @@ extension MetaRelationship: Codable {
     }
 }
 
+fileprivate protocol _Optional {}
+extension Optional: _Optional {}
+
 extension ToOneRelationship: Codable where Identifiable.ID: OptionalId {
     public init(from decoder: Decoder) throws {
         let container = try decoder.container(keyedBy: ResourceLinkageCodingKeys.self)
@@ -295,7 +298,15 @@ extension ToOneRelationship: Codable where Identifiable.ID: OptionalId {
                     )
                 )
             }
-            guard let noIdMeta = NoIdMetadata() as? IdMetaType else {
+            // if we know we aren't getting any Resource Identifer Object at all
+            // (which we do inside this block) then we better either be expecting
+            // no Id Metadata or optional Id Metadata or else we will report an
+            // error.
+            if let noIdMeta = NoIdMetadata() as? IdMetaType {
+                idMeta = noIdMeta
+            } else if let nilMeta = anyNil as? IdMetaType {
+                idMeta = nilMeta
+            } else {
                 throw DecodingError.valueNotFound(
                     Self.self,
                     DecodingError.Context(
@@ -304,7 +315,6 @@ extension ToOneRelationship: Codable where Identifiable.ID: OptionalId {
                     )
                 )
             }
-            idMeta = noIdMeta
             id = val
             return
         }
@@ -425,7 +435,7 @@ extension ToManyRelationship: Codable {
 
             newIds.append(.init(id: Relatable.ID(rawValue: id), meta: idMeta) )
         }
-        metaIds = newIds
+        idsWithMeta = newIds
     }
 
     public func encode(to encoder: Encoder) throws {
@@ -441,7 +451,7 @@ extension ToManyRelationship: Codable {
 
         var identifiers = container.nestedUnkeyedContainer(forKey: .data)
 
-        for id in metaIds {
+        for id in idsWithMeta {
             var identifier = identifiers.nestedContainer(keyedBy: ResourceIdentifierCodingKeys.self)
 
             try identifier.encode(id.id.rawValue, forKey: .id)

Tests/JSONAPITests/Relationships/RelationshipTests.swift

@@ -31,6 +31,26 @@ class RelationshipTests: XCTestCase {
 		XCTAssertEqual(relationship.ids.count, 4)
 		XCTAssertEqual(relationship.ids, [entity1, entity2, entity3, entity4].map(\.id))
 	}
+
+    func test_initToOneWithIdMeta() {
+        let entity1 = TestEntity1(attributes: .none, relationships: .none, meta: .none, links: .none)
+        let relationship = ToOneWithMetaInIds(
+            id: (entity1.id, .init(a: "hello"))
+        )
+        XCTAssertEqual(relationship.id, entity1.id)
+        XCTAssertEqual(relationship.idMeta, .init(a: "hello"))
+    }
+
+    func test_initToManyWithIdMeta() {
+        let entity1 = TestEntity1(attributes: .none, relationships: .none, meta: .none, links: .none)
+        let relationship = ToManyWithMetaInIds(
+            idsWithMetadata: [
+                (entity1.id, .init(a: "hello"))
+            ]
+        )
+        XCTAssertEqual(relationship.ids, [entity1.id])
+        XCTAssertEqual(relationship.idsWithMeta, [.init(id: entity1.id, meta: .init(a: "hello"))])
+    }
 }
 
 // MARK: - Encode/Decode
@@ -181,7 +201,7 @@ extension RelationshipTests {
                                    data: to_many_relationship_with_meta_inside_identifier)
 
         XCTAssertEqual(relationship.ids.map(\.rawValue), ["2DF03B69-4B0A-467F-B52E-B0C9E44FCECF", "90F03B69-4DF1-467F-B52E-B0C9E44FC333", "2DF03B69-4B0A-467F-B52E-B0C9E44FCECF"])
-        XCTAssertEqual(relationship.metaIds[0].meta.a, "hello")
+        XCTAssertEqual(relationship.idsWithMeta[0].meta.a, "hello")
     }
 
     func test_ToManyRelationshipWithMetaInsideIdentifier_encode() {
@@ -234,6 +254,10 @@ extension RelationshipTests {
 
 		XCTAssertEqual(encoded(value: relationship1), encoded(value: relationship2))
 	}
+
+    func test_nullableIdMeta() {
+        let _ = decoded(type: ToOneRelationship<TestEntity1?, TestMeta?, NoMetadata, NoLinks>.self, data: to_one_relationship_nulled_out)
+    }
 }
 
 // MARK: Failure tests
@@ -245,6 +269,10 @@ extension RelationshipTests {
 	func test_ToOneTypeMismatch() {
 		XCTAssertThrowsError(try JSONDecoder().decode(ToOneRelationship<TestEntity1, NoIdMetadata, NoMetadata, NoLinks>.self, from: to_one_relationship_type_mismatch))
 	}
+
+    func test_toOneNulledOutWithExpectedIdMetadata() {
+        XCTAssertThrowsError(try JSONDecoder().decode(ToOneRelationship<TestEntity1?, TestMeta, NoMetadata, NoLinks>.self, from: to_one_relationship_nulled_out))
+    }
 }
 
 // MARK: - Test types

Tests/JSONAPITests/Relationships/stubs/RelationshipStubs.swift

@@ -41,6 +41,12 @@ let to_one_relationship = """
 }
 """.data(using: .utf8)!
 
+let to_one_relationship_nulled_out = """
+{
+    "data": null
+}
+""".data(using: .utf8)!
+
 let to_one_relationship_type_mismatch = """
 {
 	"data": {