swift - 核心数据 : Failed to find a unique match for an NSEntityDescription

Question

我相当确定 CoreData 会抛出标题错误，因为函数 addNewGoal 中的行 let newGoal = Goal(context: viewContext) 。但我不知道另一种方法来“重新表述”我的函数。

相同错误的 stackoverflow 搜索结果似乎与我这里的问题无关。 (一个是通过使用静态变量而不是惰性变量解决的；另一个是关于这个错误随机发生的)

提前谢谢

(如果这是一个愚蠢的问题，我深表歉意。我是一个通过构建项目来学习的初学者。CoreData 对于我的项目概念至关重要，但我完全超出了我的能力范围，它让我内心崩溃。)

import CoreData

struct PersistenceController {
    static let shared = PersistenceController()

    static var preview: PersistenceController = {
        let result = PersistenceController(inMemory: true)
        let viewContext = result.container.viewContext
        for _ in 0..<10 {
            let newItem = Goal(context: viewContext)
            
        }
        do {
            try viewContext.save()
        } catch {

            let nsError = error as NSError
            fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
        }
        return result
    }()

    let container: NSPersistentContainer

    init(inMemory: Bool = false) {
        container = NSPersistentContainer(name: "Project")
        if inMemory {
            container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")
        }
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error as NSError? {

                fatalError("Unresolved error \(error), \(error.userInfo)")
            }
        })
    }
    
    func addNewGoal() {
        let result = PersistenceController(inMemory: true)
        let viewContext = result.container.viewContext
        let newGoal = Goal(context: viewContext)
        newGoal.passed = true
        newGoal.title = "New Goal \(Date())"
        newGoal.date = Date()
    }
    
    func addNewFail() {
        let result = PersistenceController(inMemory: true)
        let viewContext = result.container.viewContext
        let newGoal = Goal(context: viewContext)
        newGoal.passed = false
        newGoal.title = "New Goal \(Date())"
        newGoal.date = Date()
    }
    
}

错误

2021-08-11 05:05:44.981041+0800 Project[27243:1370905] [error] warning: Multiple NSEntityDescriptions claim the NSManagedObject subclass 'Goal' so +entity is unable to disambiguate.
CoreData: warning: Multiple NSEntityDescriptions claim the NSManagedObject subclass 'Goal' so +entity is unable to disambiguate.

2021-08-11 05:05:44.981226+0800 Project[27243:1370905] [error] warning:      'Goal' (0x6000032cc370) from NSManagedObjectModel (0x6000026fa7b0) claims 'Goal'.
CoreData: warning:       'Goal' (0x6000032cc370) from NSManagedObjectModel (0x6000026fa7b0) claims 'Goal'.

2021-08-11 05:05:44.981343+0800 Project[27243:1370905] [error] warning:      'Goal' (0x6000032d5e40) from NSManagedObjectModel (0x6000026bc5f0) claims 'Goal'.
CoreData: warning:       'Goal' (0x6000032d5e40) from NSManagedObjectModel (0x6000026bc5f0) claims 'Goal'.

2021-08-11 05:05:44.981447+0800 Project[27243:1370905] [error] error: +[Goal entity] Failed to find a unique match for an NSEntityDescription to a managed object subclass
CoreData: error: +[Goal entity] Failed to find a unique match for an NSEntityDescription to a managed object subclass

编辑:

Answer 1

首先，摆脱:

let result = PersistenceController(inMemory: true)

行并创建下一行:

let viewContext = container.viewContext

您已经将 container 变量范围限定为整个结构，因此它可以在 PersistenceController 结构中使用。

你的函数是这样的:

func addNewGoal() {
    let viewContext = container.viewContext
    let newGoal = Goal(context: viewContext)
    newGoal.passed = true
    newGoal.title = "New Goal \(Date())"
    newGoal.date = Date()
}

关于错误，根据this answer问题是由于同时加载两个模型引起的，并且通过调用 PersistenceController(inMemory: true) 我认为您可能已经做到了这一点。

此外，拥有 shared var 的全部意义在于，您只使用 PersistenceController 的一个实例。您当然不想通过传递已初始化的 inMemory: true 来初始化它。