多个 NSEntityDescription 声明 NSManagedObject 子类

我正在创建一个允许我使用核心数据的框架。在框架的测试目标中，我配置了一个名为的数据模型MockModel.xcdatamodeld。它包含一个名为MockManaged有一个单一的Date财产。

为了测试我的逻辑，我正在创建一个内存存储。当我想验证我的保存逻辑时，我创建内存存储的实例并使用它。但是，我不断在控制台中收到以下输出：

2018-08-14 20:35:45.340157-0400 xctest[7529:822360] [error] warning: Multiple NSEntityDescriptions claim the NSManagedObject subclass 'LocalPersistenceTests.MockManaged' so +entity is unable to disambiguate.
CoreData: warning: Multiple NSEntityDescriptions claim the NSManagedObject subclass 'LocalPersistenceTests.MockManaged' so +entity is unable to disambiguate.
2018-08-14 20:35:45.340558-0400 xctest[7529:822360] [error] warning:     'MockManaged' (0x7f986861cae0) from NSManagedObjectModel (0x7f9868604090) claims 'LocalPersistenceTests.MockManaged'.
CoreData: warning:       'MockManaged' (0x7f986861cae0) from NSManagedObjectModel (0x7f9868604090) claims 'LocalPersistenceTests.MockManaged'.
2018-08-14 20:35:45.340667-0400 xctest[7529:822360] [error] warning:     'MockManaged' (0x7f986acc4d10) from NSManagedObjectModel (0x7f9868418ee0) claims 'LocalPersistenceTests.MockManaged'.
CoreData: warning:       'MockManaged' (0x7f986acc4d10) from NSManagedObjectModel (0x7f9868418ee0) claims 'LocalPersistenceTests.MockManaged'.
2018-08-14 20:35:45.342938-0400 xctest[7529:822360] [error] error: +[LocalPersistenceTests.MockManaged entity] Failed to find a unique match for an NSEntityDescription to a managed object subclass
CoreData: error: +[LocalPersistenceTests.MockManaged entity] Failed to find a unique match for an NSEntityDescription to a managed object subclass

下面是我用来创建内存存储的对象：

class MockNSManagedObjectContextCreator {

    // MARK: - NSManagedObjectContext Creation

    static func inMemoryContext() -> NSManagedObjectContext {
        guard let model = NSManagedObjectModel.mergedModel(from: [Bundle(for: self)]) else { fatalError("Could not create model") }
        let coordinator = NSPersistentStoreCoordinator(managedObjectModel: model)
        do {
            try coordinator.addPersistentStore(ofType: NSInMemoryStoreType, configurationName: nil, at: nil, options: nil)
        } catch {
            fatalError("Could not create in-memory store")
        }
        let context = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
        context.persistentStoreCoordinator = coordinator
        return context
    }

}

下面是我的构成MockManaged entity:

class MockManaged: NSManagedObject, Managed {

    // MARK: - Properties

    @NSManaged var date: Date

}

下面是我的构成XCTestCase:

class Tests_NSManagedObjectContext: XCTestCase {

    // MARK: - Object Insertion

    func test_NSManagedObjectContext_InsertsManagedObject_WhenObjectConformsToManagedProtocol() {
        let context = MockNSManagedObjectContextCreator.inMemoryContext()
        let changeExpectation = expectation(forNotification: .NSManagedObjectContextObjectsDidChange, object: context, handler: nil)
        let object: MockManaged = context.insertObject()
        object.date = Date()
        wait(for: [changeExpectation], timeout: 2)
    }

    // MARK: - Saving

    func test_NSManagedObjectContext_Saves_WhenChangesHaveBeenMade() {
        let context = MockNSManagedObjectContextCreator.inMemoryContext()
        let saveExpectation = expectation(forNotification: .NSManagedObjectContextDidSave, object: context, handler: nil)
        let object: MockManaged = context.insertObject()
        object.date = Date()
        do {
            try context.saveIfHasChanges()
        } catch {
            XCTFail("Expected successful save")
        }
        wait(for: [saveExpectation], timeout: 2)
    }

    func test_NSManagedObjectContext_DoesNotSave_WhenNoChangesHaveBeenMade() {
        let context = MockNSManagedObjectContextCreator.inMemoryContext()
        let saveExpectation = expectation(forNotification: .NSManagedObjectContextDidSave, object: context, handler: nil)
        saveExpectation.isInverted = true
        do {
            try context.saveIfHasChanges()
        } catch {
            XCTFail("Unexpected error: \(error)")
        }
        wait(for: [saveExpectation], timeout: 2)
    }

}

我在做什么导致测试中出现错误？

自动缓存后

这不应该再发生了NSPersistent[CloudKit]Container(name: String)，因为它现在似乎会自动缓存模型（Swift 5.1、Xcode 11、iOS13/MacOS V10.15）。

预自动缓存

NSPersistentContainer/NSPersistentCloudKitContainer确实有两个构造函数：

• 初始化（名称：字符串） https://developer.apple.com/documentation/coredata/nspersistentcontainer/1640557-init
• 初始化（名称：字符串， ManagedObjectModel模型：NSManagedObjectModel） https://developer.apple.com/documentation/coredata/nspersistentcontainer/1640584-init

第一个只是一个方便的初始化程序，使用从磁盘加载的模型调用第二个。问题是加载相同的NSManagedObjectModel两次从同一磁盘内app/test invocation导致上述错误，因为每次加载模型都会导致外部注册调用，一旦调用第二次，就会打印错误app/test invocation. And init(name: String) was不够智能，无法缓存模型。

因此，如果您想多次加载容器，则必须加载NSManagedObjectModel一次并将其存储在一个属性中，然后在每个属性中使用init(name:managedObjectModel:) call.

示例：缓存模型

import Foundation
import SwiftUI
import CoreData
import CloudKit

class PersistentContainer {
    private static var _model: NSManagedObjectModel?
    private static func model(name: String) throws -> NSManagedObjectModel {
        if _model == nil {
            _model = try loadModel(name: name, bundle: Bundle.main)
        }
        return _model!
    }
    private static func loadModel(name: String, bundle: Bundle) throws -> NSManagedObjectModel {
        guard let modelURL = bundle.url(forResource: name, withExtension: "momd") else {
            throw CoreDataError.modelURLNotFound(forResourceName: name)
        }

        guard let model = NSManagedObjectModel(contentsOf: modelURL) else {
            throw CoreDataError.modelLoadingFailed(forURL: modelURL)
       }
        return model
    }

    enum CoreDataError: Error {
        case modelURLNotFound(forResourceName: String)
        case modelLoadingFailed(forURL: URL)
    }

    public static func container() throws -> NSPersistentCloudKitContainer {
        let name = "ItmeStore"
        return NSPersistentCloudKitContainer(name: name, managedObjectModel: try model(name: name))
    }
}

旧答案

加载核心数据有点神奇，从磁盘加载模型并使用它意味着它会注册某些类型。第二次加载尝试再次注册该类型，这显然告诉您已经为该类型注册了某些内容。

您只能加载一次核心数据，并在每次测试后清理该实例。清理意味着删除每个对象实体然后保存。有一些函数可以为您提供所有实体，然后您可以获取和删除这些实体。批量删除在内存中不可用，但它是逐个托管对象存在的。

（可能更简单）的替代方案是加载模型一次，将其存储在某个地方，然后在每次调用时重用该模型。NSPersistentContainer调用时，它有一个构造函数来使用给定的模型，而不是从磁盘再次加载它。