Merge pull request #41 from mattpolzin/feature/resource-object-replacing

Resource Object replacing and tapping

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

@@ -12,25 +12,6 @@ import JSONAPI
 
  ********/
 
-// Mapping functions (will be included in future version of library)
-extension JSONAPI.ResourceObject {
-    func mapAttributes(_ transform: (Description.Attributes) -> Description.Attributes) -> Self {
-        return Self(id: id,
-                    attributes: transform(attributes),
-                    relationships: relationships,
-                    meta: meta,
-                    links: links)
-    }
-
-    func mapRelationships(_ transform: (Description.Relationships) -> Description.Relationships) -> Self {
-        return Self(id: id,
-                    attributes: attributes,
-                    relationships: transform(relationships),
-                    meta: meta,
-                    links: links)
-    }
-}
-
 // Mock up a server response
 let mockDogData = """
 {
@@ -62,11 +43,7 @@ var dog = parsedResponse.body.primaryResource!.value
 print("Received dog named: \(dog.name)")
 
 // change the dog's name
-let changedDog = dog.mapAttributes { currentAttributes in
-    var ret = currentAttributes
-    ret.name = .init(value: "Julia")
-    return ret
-}
+let changedDog = dog.tappingAttributes { $0.name = .init(value: "Julia") }
 
 // create a document to be used as a request body for a PATCH request
 let patchRequest = MutableDogDocument(apiDescription: .none,
@@ -97,7 +74,7 @@ var dog2 = parsedResponse2.body.primaryResource!.value
 print("Received dog named: \(dog2.name)")
 
 // change the dog's name
-let changedDog2 = dog2.mapAttributes { _ in
+let changedDog2 = dog2.replacingAttributes { _ in
     return .init(name: .init(value: "Nigel"))
 }
 
@@ -130,7 +107,7 @@ var dog3 = parsedResponse2.body.primaryResource!.value
 print("Received dog with owner: \(dog3 ~> \.owner)")
 
 // give the dog an owner
-let changedDog3 = dog3.mapRelationships { _ in
+let changedDog3 = dog3.replacingRelationships { _ in
     return .init(owner: .init(id: Id(rawValue: "1")))
 }
 

README.md

@@ -76,6 +76,9 @@ This library works well when used by both the server responsible for serializati
 		- [Sparse Fieldsets](#sparse-fieldsets)
 			- [Supporting Sparse Fieldset Encoding](#supporting-sparse-fieldset-encoding)
 			- [Sparse Fieldset `typealias` comparisons](#sparse-fieldset-typealias-comparisons)
+		- [Replacing and Tapping Attributes/Relationships](#replacing-and-tapping-attributesrelationships)
+			- [Tapping](#tapping)
+			- [Replacing](#replacing)
 		- [Custom Attribute or Relationship Key Mapping](#custom-attribute-or-relationship-key-mapping)
 		- [Custom Attribute Encode/Decode](#custom-attribute-encodedecode)
 		- [Meta-Attributes](#meta-attributes)
@@ -569,6 +572,35 @@ In order to support sparse fieldsets (which are encode-only), the following comp
 typealias SparseDocument<PrimaryResourceBody: JSONAPI.EncodableResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, BasicJSONAPIError<String>>
 ```
 
+### Replacing and Tapping Attributes/Relationships
+When you are working with an immutable Resource Object, it can be useful to replace its attributes or relationships. As a client, you might receive a resource from the server, update something, and then send the server a PATCH request.
+
+`ResourceObject` is immutable, but you can create a new copy of a `ResourceObject` having updated attributes or relationships.
+
+#### Tapping
+If your `Attributes` or `Relationships` struct is mutable (i.e. its properties are `var`s) then you may find `ResourceObject`'s `tappingAttributes()` and `tappingRelationships()` functions useful. For both, you pass a function that takes an `inout` copy of the respective object or value that you can mutate. The mutated value is then used to create a new `ResourceObject`.
+
+For example, to take a hypothetical `Dog` resource object and change the name attribute:
+```swift
+let resourceObject = Dog(...)
+
+let newResourceObject = resourceObject
+	.tappingAttributes { $0.name = .init(value: "Charlie") }
+```
+
+#### Replacing
+If your `Attributes` or `Relationships` struct is immutable (i.e. its properties are `let`s) then you may find `ResourceObject`'s `replacingAttributes()` and `replacingRelationships()` functions useful. For both, you pass a function that takes the current attributes or relationships and you return a new value. The new value is then used to create a new `ResourceObject`.
+
+For example, to take a hypothetical `Dog` resource object and change the name attribute:
+```swift
+let resourceObject = Dog(...)
+
+let newResourceObject = resourceObject
+	.replacingAttributes { _ in
+		return Dog.Attributes(name: .init(value: "Charlie"))
+}
+```
+
 ### Custom Attribute or Relationship Key Mapping
 There is not anything special going on at the `JSONAPI.Attributes` and `JSONAPI.Relationships` levels, so you can easily provide custom key mappings by taking advantage of `Codable`'s `CodingKeys` pattern. Here are two models that will encode/decode equivalently but offer different naming in your codebase:
 ```swift

Sources/JSONAPI/Resource/Resource Object/ResourceObject+Replacing.swift

@@ -0,0 +1,74 @@
+//
+//  ResourceObject+Replacing.swift
+//  JSONAPI
+//
+//  Created by Mathew Polzin on 10/12/19.
+//
+
+public extension JSONAPI.ResourceObject {
+    /// Return a new `ResourceObject`, having replaced `self`'s
+    /// `attributes` with the attributes returned by the given
+    /// replacement function.
+    ///
+    /// - important: `self` is not mutated. A copy of self is returned.
+    ///
+    /// - parameters:
+    ///     - replacement: A function that takes the existing `attributes` and returns the replacement.
+    func replacingAttributes(_ replacement: (Description.Attributes) -> Description.Attributes) -> Self {
+        return Self(id: id,
+                    attributes: replacement(attributes),
+                    relationships: relationships,
+                    meta: meta,
+                    links: links)
+    }
+
+    /// Return a new `ResourceObject`, having updated `self`'s
+    /// `attributes` with the tap function given.
+    ///
+    /// - important: `self` is not mutated. A copy of self is returned.
+    ///
+    /// - parameters:
+    ///     - tap: A function that takes a copy of the existing `attributes` and mutates them.
+    func tappingAttributes(_ tap: (inout Description.Attributes) -> Void) -> Self {
+        var newAttributes = attributes
+        tap(&newAttributes)
+        return Self(id: id,
+                    attributes: newAttributes,
+                    relationships: relationships,
+                    meta: meta,
+                    links: links)
+    }
+
+    /// Return a new `ResourceObject`, having replaced `self`'s
+    /// `relationships` with the `relationships` returned by the given
+    /// replacement function.
+    ///
+    /// - important: `self` is not mutated. A copy of self is returned.
+    ///
+    /// - parameters:
+    ///     - replacement: A function that takes the existing relationships and returns the replacement.
+    func replacingRelationships(_ replacement: (Description.Relationships) -> Description.Relationships) -> Self {
+        return Self(id: id,
+                    attributes: attributes,
+                    relationships: replacement(relationships),
+                    meta: meta,
+                    links: links)
+    }
+
+    /// Return a new `ResourceObject`, having updated `self`'s
+    /// `relationships` with the tap function given.
+    ///
+    /// - important: `self` is not mutated. A copy of self is returned.
+    ///
+    /// - parameters:
+    ///     - tap: A function that takes a copy of the existing `relationships` and mutates them.
+    func tappingRelationships(_ tap: (inout Description.Relationships) -> Void) -> Self {
+        var newRelationships = relationships
+        tap(&newRelationships)
+        return Self(id: id,
+                    attributes: attributes,
+                    relationships: newRelationships,
+                    meta: meta,
+                    links: links)
+    }
+}

Tests/JSONAPITests/ResourceObject/ResourceObject+ReplacingTests.swift

@@ -0,0 +1,155 @@
+//
+//  ResourceObject+ReplacingTests.swift
+//  JSONAPITests
+//
+//  Created by Mathew Polzin on 10/12/19.
+//
+
+import XCTest
+import JSONAPI
+
+final class ResourceObjectReplacingTests: XCTestCase {
+    func test_replaceMutableAttributes() {
+        let testResource = MutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                           relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                           meta: .none,
+                                           links: .none)
+
+        let mutatedResource = testResource
+            .replacingAttributes {
+                var newAttributes = $0
+                newAttributes.name = .init(value: "Matt 2")
+                return newAttributes
+        }
+
+        XCTAssertEqual(testResource.name, "Matt")
+        XCTAssertEqual(mutatedResource.name, "Matt 2")
+    }
+
+    func test_tapMutableAttributes() {
+        let testResource = MutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                           relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                           meta: .none,
+                                           links: .none)
+
+        let mutatedResource = testResource
+            .tappingAttributes { $0.name = .init(value: "Matt 2") }
+
+        XCTAssertEqual(testResource.name, "Matt")
+        XCTAssertEqual(mutatedResource.name, "Matt 2")
+    }
+
+    func test_replaceImmutableAttributes() {
+        let testResource = ImmutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                             relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                             meta: .none,
+                                             links: .none)
+
+        let mutatedResource = testResource
+            .replacingAttributes {
+                return .init(name: $0.name.map { $0 + " 2" })
+        }
+
+        XCTAssertEqual(testResource.name, "Matt")
+        XCTAssertEqual(mutatedResource.name, "Matt 2")
+    }
+
+    func test_tapImmutableAttributes() {
+        let testResource = ImmutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                             relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                             meta: .none,
+                                             links: .none)
+
+        let mutatedResource = testResource
+            .tappingAttributes { $0 = .init(name: $0.name.map { $0 + " 2" }) }
+
+        XCTAssertEqual(testResource.name, "Matt")
+        XCTAssertEqual(mutatedResource.name, "Matt 2")
+    }
+
+    func test_replaceMutableRelationships() {
+        let testResource = MutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                           relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                           meta: .none,
+                                           links: .none)
+
+        let mutatedResource = testResource
+            .replacingRelationships {
+                var newRelationships = $0
+                newRelationships.other = .init(id: .init(rawValue: "3"))
+                return newRelationships
+        }
+
+        XCTAssertEqual(testResource ~> \.other, "2")
+        XCTAssertEqual(mutatedResource ~> \.other, "3")
+    }
+
+    func test_tapMutableRelationships() {
+        let testResource = MutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                           relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                           meta: .none,
+                                           links: .none)
+
+        let mutatedResource = testResource
+            .tappingRelationships { $0.other = .init(id: .init(rawValue: "3")) }
+
+        XCTAssertEqual(testResource ~> \.other, "2")
+        XCTAssertEqual(mutatedResource ~> \.other, "3")
+    }
+
+    func test_replaceImmutableRelationships() {
+        let testResource = ImmutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                             relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                             meta: .none,
+                                             links: .none)
+
+        let mutatedResource = testResource
+            .replacingRelationships { _ in
+                return .init(other: .init(id: .init(rawValue: "3")))
+        }
+
+        XCTAssertEqual(testResource ~> \.other, "2")
+        XCTAssertEqual(mutatedResource ~> \.other, "3")
+    }
+
+    func test_tapImmutableRelationships() {
+        let testResource = ImmutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                             relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                             meta: .none,
+                                             links: .none)
+
+        let mutatedResource = testResource
+            .tappingRelationships { $0 = .init(other: .init(id: .init(rawValue: "3"))) }
+
+        XCTAssertEqual(testResource ~> \.other, "2")
+        XCTAssertEqual(mutatedResource ~> \.other, "3")
+    }
+}
+
+private enum MutableTestDescription: JSONAPI.ResourceObjectDescription {
+    static let jsonType: String = "test"
+
+    struct Attributes: JSONAPI.Attributes {
+        var name: Attribute<String>
+    }
+
+    struct Relationships: JSONAPI.Relationships {
+        var other: ToOneRelationship<MutableTestType, NoMetadata, NoLinks>
+    }
+}
+
+private typealias MutableTestType = JSONAPI.ResourceObject<MutableTestDescription, NoMetadata, NoLinks, String>
+
+private enum ImmutableTestDescription: JSONAPI.ResourceObjectDescription {
+    static let jsonType: String = "test2"
+
+    struct Attributes: JSONAPI.Attributes {
+        let name: Attribute<String>
+    }
+
+    struct Relationships: JSONAPI.Relationships {
+        let other: ToOneRelationship<ImmutableTestType, NoMetadata, NoLinks>
+    }
+}
+
+private typealias ImmutableTestType = JSONAPI.ResourceObject<ImmutableTestDescription, NoMetadata, NoLinks, String>