entityForName: nil 不是用于搜索实体名称的合法 NSPersistentStoreCoordinator答案

【问题标题】：entityForName: nil is not a legal NSPersistentStoreCoordinator for searching for entity nameentityForName: nil 不是用于搜索实体名称的合法 NSPersistentStoreCoordinator
【发布时间】：2020-05-09 22:30:03
【问题描述】：

我设置了一个 DatabaseApplicationService

获取以编程方式定义的 NSManagedObjectModel
基于此模型创建一个 NSPersistentCloudKitContainer，具有“本地”和“云”两个配置。

看起来一切正常。

    lazy var persistentContainer: NSPersistentCloudKitContainer = {

        // Ensure that we have the required path.
        pathHandler.ensurePersistentStorePath()

        #if DEBUG
        // get the store description
        guard let description = container.persistentStoreDescriptions.first
            else {
                fatalError("Could not retrieve a persistent store description.")
            }

        // initialize the CloudKit schema
        try? container.initializeCloudKitSchema(options: NSPersistentCloudKitContainerSchemaInitializationOptions.dryRun)

        #endif

        let local = NSPersistentStoreDescription(url: pathHandler.persistentLocalStoreURL)
        local.configuration = "Local"

        let cloud = NSPersistentStoreDescription(url: pathHandler.persistentCloudStoreURL)
        cloud.configuration = "Cloud"

        cloud.cloudKitContainerOptions = NSPersistentCloudKitContainerOptions(containerIdentifier: "iCloud.com.innoreq.HappyFreelancer")
        container.persistentStoreDescriptions = [ local, cloud ]

        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
    }()

在SceneDelegate中，环境获取了注入的NSManagedObjectContext：

        let contentView = ContentView().environment(\.managedObjectContext, databaseService.context)

在视图的模型中，环境被要求提供上下文：

    @Environment(\.managedObjectContext) var managedObjectContext: NSManagedObjectContext

现在，从上下文中获取数据时：

let fetchRequest: NSFetchRequest<NSFetchRequestResult> = NSFetchRequest(entityName: "EWork")

        do {

            return try managedObjectContext.execute(fetchRequest) as! [IsTimedAndTagged]
        } catch {

            fatalError("Failed to fetch EWork")
        }

这个错误在运行时抛出：

2020-01-23 16:34:05.981483+0100 XY[14121:20859222] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '+entityForName: nil is not a legal NSPersistentStoreCoordinator for searching for entity name 'EWork''

检查服务的协调器时，它不是 nil。这种奇怪的效果有什么解释吗？

【问题讨论】：

你的意思是managedObjectContext.fetch(fetchRequest)而不是execute？
改变了，现在有同样的最终错误，但之前有一个警告：view context accessed for persistent container XY with no stores loaded
对以下代码有同样的问题：NSEntityDescription.entity(forEntityName: "Category", in: context) in SwiftUI
你能解决这个问题吗？

标签： swift core-data swiftui

【解决方案1】：

对于那些使用 Swift5 并且没有 Appdelegate 并尝试创建 NFSRequest 查询的人。

您可能缺少持久存储，因此创建自己的自定义存储可能会起作用。因为那是我的问题。

创建自己的 PersistentContainer 类：

import SwiftUI
import CoreData
@main
struct TestApp: App {
        let context = PersistentCloudKitContainer.persistentContainer.viewContext
        var body: some Scene {
                WindowGroup {
                        ContentView().environment(\.managedObjectContext, context)
                }
        }
}

然后你的自定义类是这样的：

import CoreData
public class PersistentCloudKitContainer {
        // MARK: - Define Constants / Variables
        public static var context: NSManagedObjectContext {
                return persistentContainer.viewContext
        }
        // MARK: - Initializer
        private init() {}
        // MARK: - Core Data stack
        public static var persistentContainer: NSPersistentContainer = {
                let container = NSPersistentContainer(name: "Model")
                container.loadPersistentStores(completionHandler: { (storeDescription, error) in
                        if let error = error as NSError? {
                                fatalError("Unresolved error \(error), \(error.userInfo)")
                        }
                })
                container.viewContext.automaticallyMergesChangesFromParent = true
                container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
                return container
        }()
        // MARK: - Core Data Saving support
        public static func saveContext () {
                let context = persistentContainer.viewContext
                if context.hasChanges {
                        do {
                                try context.save()
                        } catch {
                                let nserror = error as NSError
                                fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
                        }
                }
        }
}

希望它可以帮助像我这样的人，他们最终可能会在这里寻找答案！

【讨论】：