[Libraries] Persistence (#5)

This PR contains the work that implements the Persistence service, which is used to store and serve the data of the application.

To give further details on what was done:
- [x] created the `Persistence`library into the **Libraries** package;
- [x] defined the `Location` model into the **Model** core data model;
- [x] implemented the `PersistenceService` service;
- [x] removed the core data stack boilerplate code from the `AppDelegate` and `SceneDelegate` delegates in the *Locations* target.

Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Reviewed-on: rock-n-code/deep-linking-assignment#5

Apps/Locations/Libraries/Package.swift

@@ -27,6 +27,10 @@ let package = Package(
                 "APICore"
             ]
         ),
+        .target(
+            name: "Persistence",
+            dependencies: []
+        ),
         .testTarget(
             name: "APICoreTests",
             dependencies: [
@@ -40,5 +44,11 @@ let package = Package(
                 "Locations"
             ]
         ),
+        .testTarget(
+            name: "PersistenceTests",
+            dependencies: [
+                "Persistence"
+            ]
+        ),
     ]
 )

Apps/Locations/Libraries/Sources/Persistence/Model.xcdatamodeld/Locations.xcdatamodel/contents

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<model type="com.apple.IDECoreDataModeler.DataModel" documentVersion="1.0" lastSavedToolsVersion="21754" systemVersion="22E261" minimumToolsVersion="Automatic" sourceLanguage="Swift" userDefinedModelVersionIdentifier="">
+    <entity name="Location" representedClassName="Location" syncable="YES" codeGenerationType="class">
+        <attribute name="createdAt" attributeType="Date" usesScalarValueType="NO"/>
+        <attribute name="latitude" attributeType="Float" defaultValueString="0.0" usesScalarValueType="YES"/>
+        <attribute name="longitude" attributeType="Float" defaultValueString="0.0" usesScalarValueType="YES"/>
+        <attribute name="name" optional="YES" attributeType="String"/>
+        <attribute name="source" attributeType="Integer 16" defaultValueString="0" usesScalarValueType="YES"/>
+    </entity>
+</model>

Apps/Locations/Libraries/Sources/Persistence/Services/PersistenceService.swift

@@ -0,0 +1,133 @@
+//
+//  PersistenceService.swift
+//  Persistence
+//
+//  Created by Javier Cicchelli on 10/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import CoreData
+
+public struct PersistenceService {
+    
+    // MARK: Properties
+    
+    public static let shared = PersistenceService()
+    public static let inMemory = PersistenceService(inMemory: true)
+    
+    public let container: NSPersistentContainer
+    
+    // MARK: Initialisers
+    
+    init(inMemory: Bool = false) {
+        guard
+            let modelURL = Bundle.module.url(forResource: .Model.name, withExtension: .Model.extension),
+            let managedObjectModel = NSManagedObjectModel(contentsOf: modelURL)
+        else {
+            fatalError("Could not load the model from the library.")
+        }
+
+        container = NSPersistentContainer(
+            name: .Model.name,
+            managedObjectModel: managedObjectModel
+        )
+        
+        setContainer(inMemory)
+    }
+    
+    // MARK: Functions
+    
+    /// Create a private queue context.
+    /// - Returns: A concurrent `NSManagedObjectContext` context instance ready to use.
+    public func makeTaskContext() -> NSManagedObjectContext {
+        let taskContext = container.newBackgroundContext()
+        
+        taskContext.automaticallyMergesChangesFromParent = true
+        taskContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
+        
+        return taskContext
+    }
+    
+    /// Create a child context of the view context.
+    /// - Returns: A generated child `NSManagedObjectContext` context instance ready to use.
+    public func makeChildContext() -> NSManagedObjectContext {
+        let context = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
+        
+        context.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
+        context.parent = container.viewContext
+        context.automaticallyMergesChangesFromParent = true
+        
+        return context
+    }
+    
+    /// Save a given context,
+    /// - Parameter context: A `NSManagedObjectContext` context instance to save.
+    public func save(context: NSManagedObjectContext) {
+        guard context.hasChanges else {
+            return
+        }
+        
+        do {
+            try context.save()
+        } catch {
+            let nserror = error as NSError
+            fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
+        }
+    }
+    
+    /// Save a given child context as well as its respective parent context.
+    /// - Parameter context: A child `NSManagedObjectContext` context instance to save.
+    public func save(childContext context: NSManagedObjectContext) {
+        guard context.hasChanges else {
+            return
+        }
+        
+        do {
+            try context.save()
+            
+            guard
+                let parent = context.parent,
+                parent == container.viewContext
+            else {
+                return
+            }
+
+            try parent.performAndWait {
+                try parent.save()
+            }
+        } catch {
+            let nserror = error as NSError
+            fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
+        }
+    }
+    
+}
+
+// MARK: - Helpers
+
+private extension PersistenceService {
+    func setContainer(_ inMemory: Bool) {
+        container.persistentStoreDescriptions = [
+            NSPersistentStoreDescription(url:
+                inMemory
+                    ? URL(fileURLWithPath: "/dev/null")
+                    : NSPersistentContainer.defaultDirectoryURL().appending(path: "\(String.Model.name).sqlite")
+            )
+        ]
+        container.loadPersistentStores { _, error in
+            if let error = error as NSError? {
+                fatalError("Unresolved error \(error), \(error.userInfo)")
+            }
+        }
+        container.viewContext.automaticallyMergesChangesFromParent = true
+    }
+}
+
+// MARK: - String+Constants
+
+private extension String {
+    enum Model {
+        static let name = "Model"
+        static let `extension` = "momd"
+    }
+}

Apps/Locations/Libraries/Tests/PersistenceTests/Services/PersistenceServiceTests.swift

@@ -0,0 +1,104 @@
+//
+//  PersistenceServiceTests.swift
+//  PersistenceTests
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import CoreData
+import XCTest
+
+@testable import Persistence
+
+final class PersistenceServiceTests: XCTestCase {
+    
+    // MARK: Properties
+    
+    private var persistence: PersistenceService!
+
+    // MARK: Initialiser tests
+    
+    func test_initByDefault() {
+        // GIVEN
+        // WHEN
+        persistence = .init()
+        
+        // THEN
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.count, 1)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.type, NSSQLiteStoreType)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.url?.lastPathComponent, "Model.sqlite")
+        XCTAssertNotNil(persistence.container.viewContext)
+        XCTAssertTrue(persistence.container.viewContext.automaticallyMergesChangesFromParent)
+    }
+    
+    func test_initWithInMemory() {
+        // GIVEN
+        // WHEN
+        persistence = .init(inMemory: true)
+        
+        // THEN
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.count, 1)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.type, NSSQLiteStoreType)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.url?.absoluteString, "file:///dev/null")
+        XCTAssertNotNil(persistence.container.viewContext)
+        XCTAssertTrue(persistence.container.viewContext.automaticallyMergesChangesFromParent)
+    }
+    
+    // MARK: Static properties tests
+    
+    func test_shared() {
+        // GIVEN
+        persistence = .shared
+        
+        // WHEN
+        // THEN
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.count, 1)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.type, NSSQLiteStoreType)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.url?.lastPathComponent, "Model.sqlite")
+        XCTAssertNotNil(persistence.container.viewContext)
+        XCTAssertTrue(persistence.container.viewContext.automaticallyMergesChangesFromParent)
+    }
+    
+    func test_inMemory() {
+        // GIVEN
+        persistence = .inMemory
+        
+        // WHEN
+        // THEN
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.count, 1)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.type, NSSQLiteStoreType)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.url?.absoluteString, "file:///dev/null")
+        XCTAssertNotNil(persistence.container.viewContext)
+        XCTAssertTrue(persistence.container.viewContext.automaticallyMergesChangesFromParent)
+    }
+    
+    // MARK: Functions tests
+    
+    func test_makeTaskContext() {
+        // GIVEN
+        persistence = .inMemory
+        
+        // WHEN
+        let context = persistence.makeTaskContext()
+        
+        // THEN
+        XCTAssertTrue(context.automaticallyMergesChangesFromParent)
+        XCTAssertTrue(context.mergePolicy as AnyObject === NSMergeByPropertyObjectTrumpMergePolicy)
+        XCTAssertNil(context.parent)
+    }
+    
+    func test_makeChildContext() {
+        // GIVEN
+        persistence = .inMemory
+        
+        // WHEN
+        let context = persistence.makeChildContext()
+        
+        // THEN
+        XCTAssertTrue(context.automaticallyMergesChangesFromParent)
+        XCTAssertTrue(context.mergePolicy as AnyObject === NSMergeByPropertyObjectTrumpMergePolicy)
+        XCTAssertEqual(context.parent, persistence.container.viewContext)
+    }
+
+}

Apps/Locations/Resources/Locations.xcdatamodeld/Locations.xcdatamodel/contents

@@ -1,4 +0,0 @@
-<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
-<model type="com.apple.IDECoreDataModeler.DataModel" documentVersion="1.0" lastSavedToolsVersion="1" systemVersion="11A491" minimumToolsVersion="Automatic" sourceLanguage="Swift" usedWithCloudKit="false" userDefinedModelVersionIdentifier="">
-    <elements/>
-</model>

Apps/Locations/Sources/AppDelegate.swift

@@ -41,50 +41,5 @@ class AppDelegate: UIResponder, UIApplicationDelegate {
         // Use this method to release any resources that were specific to the discarded scenes, as they will not return.
     }
 
-    // MARK: - Core Data stack
-
-    lazy var persistentContainer: NSPersistentContainer = {
-        /*
-         The persistent container for the application. This implementation
-         creates and returns a container, having loaded the store for the
-         application to it. This property is optional since there are legitimate
-         error conditions that could cause the creation of the store to fail.
-        */
-        let container = NSPersistentContainer(name: "Locations")
-        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
-            if let error = error as NSError? {
-                // Replace this implementation with code to handle the error appropriately.
-                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
-                 
-                /*
-                 Typical reasons for an error here include:
-                 * The parent directory does not exist, cannot be created, or disallows writing.
-                 * The persistent store is not accessible, due to permissions or data protection when the device is locked.
-                 * The device is out of space.
-                 * The store could not be migrated to the current model version.
-                 Check the error message to determine what the actual problem was.
-                 */
-                fatalError("Unresolved error \(error), \(error.userInfo)")
-            }
-        })
-        return container
-    }()
-
-    // MARK: - Core Data Saving support
-
-    func saveContext () {
-        let context = persistentContainer.viewContext
-        if context.hasChanges {
-            do {
-                try context.save()
-            } catch {
-                // Replace this implementation with code to handle the error appropriately.
-                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
-                let nserror = error as NSError
-                fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
-            }
-        }
-    }
-
 }
 

Apps/Locations/Sources/SceneDelegate.swift

@@ -62,7 +62,6 @@ class SceneDelegate: UIResponder, UIWindowSceneDelegate {
         // to restore the scene back to its current state.
         
         // Save changes in the application's managed object context when the application transitions to the background.
-        (UIApplication.shared.delegate as? AppDelegate)?.saveContext()
     }
     
 }

DeepLinking.xcodeproj/project.pbxproj

@@ -10,7 +10,6 @@
 		46EB331B29E1CE04001D5EAF /* AppDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 46EB331A29E1CE04001D5EAF /* AppDelegate.swift */; };
 		46EB331D29E1CE04001D5EAF /* SceneDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 46EB331C29E1CE04001D5EAF /* SceneDelegate.swift */; };
 		46EB331F29E1CE04001D5EAF /* ViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 46EB331E29E1CE04001D5EAF /* ViewController.swift */; };
-		46EB332529E1CE04001D5EAF /* Locations.xcdatamodeld in Sources */ = {isa = PBXBuildFile; fileRef = 46EB332329E1CE04001D5EAF /* Locations.xcdatamodeld */; };
 		46EB332729E1CE05001D5EAF /* Assets.xcassets in Resources */ = {isa = PBXBuildFile; fileRef = 46EB332629E1CE05001D5EAF /* Assets.xcassets */; };
 		46EB332A29E1CE05001D5EAF /* LaunchScreen.storyboard in Resources */ = {isa = PBXBuildFile; fileRef = 46EB332829E1CE05001D5EAF /* LaunchScreen.storyboard */; };
 		46EB334429E1D1EC001D5EAF /* Libraries in Frameworks */ = {isa = PBXBuildFile; productRef = 46EB334329E1D1EC001D5EAF /* Libraries */; };
@@ -117,7 +116,6 @@
 		46EB331A29E1CE04001D5EAF /* AppDelegate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AppDelegate.swift; sourceTree = "<group>"; };
 		46EB331C29E1CE04001D5EAF /* SceneDelegate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SceneDelegate.swift; sourceTree = "<group>"; };
 		46EB331E29E1CE04001D5EAF /* ViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ViewController.swift; sourceTree = "<group>"; };
-		46EB332429E1CE04001D5EAF /* Locations.xcdatamodel */ = {isa = PBXFileReference; lastKnownFileType = wrapper.xcdatamodel; path = Locations.xcdatamodel; sourceTree = "<group>"; };
 		46EB332629E1CE05001D5EAF /* Assets.xcassets */ = {isa = PBXFileReference; lastKnownFileType = folder.assetcatalog; path = Assets.xcassets; sourceTree = "<group>"; };
 		46EB332929E1CE05001D5EAF /* Base */ = {isa = PBXFileReference; lastKnownFileType = file.storyboard; name = Base; path = Base.lproj/LaunchScreen.storyboard; sourceTree = "<group>"; };
 		46EB332B29E1CE05001D5EAF /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
@@ -214,7 +212,6 @@
 				46EB332629E1CE05001D5EAF /* Assets.xcassets */,
 				46EB332B29E1CE05001D5EAF /* Info.plist */,
 				46EB332829E1CE05001D5EAF /* LaunchScreen.storyboard */,
-				46EB332329E1CE04001D5EAF /* Locations.xcdatamodeld */,
 			);
 			path = Resources;
 			sourceTree = "<group>";
@@ -412,7 +409,6 @@
 			files = (
 				46EB331F29E1CE04001D5EAF /* ViewController.swift in Sources */,
 				46EB331B29E1CE04001D5EAF /* AppDelegate.swift in Sources */,
-				46EB332529E1CE04001D5EAF /* Locations.xcdatamodeld in Sources */,
 				46EB331D29E1CE04001D5EAF /* SceneDelegate.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
@@ -644,19 +640,6 @@
 			productName = Shared;
 		};
 /* End XCSwiftPackageProductDependency section */
-
-/* Begin XCVersionGroup section */
-		46EB332329E1CE04001D5EAF /* Locations.xcdatamodeld */ = {
-			isa = XCVersionGroup;
-			children = (
-				46EB332429E1CE04001D5EAF /* Locations.xcdatamodel */,
-			);
-			currentVersion = 46EB332429E1CE04001D5EAF /* Locations.xcdatamodel */;
-			path = Locations.xcdatamodeld;
-			sourceTree = "<group>";
-			versionGroupType = wrapper.xcdatamodel;
-		};
-/* End XCVersionGroup section */
 	};
 	rootObject = 46EB325129E1BBD1001D5EAF /* Project object */;
 }