在 Swift 3 中启用核心数据轻量级迁移 [英] Enabling core data lightweight migration in Swift 3

问题描述

根据我阅读的文章，启用核心数据轻量级迁移的正确方法是将选项传递给 addPersistentStoreWithType:

According to the articles I have read the correct way to enable core data light weight migrations is by passing options to addPersistentStoreWithType:

let mOptions = [NSMigratePersistentStoresAutomaticallyOption: true,
NSInferMappingModelAutomaticallyOption: true]

try coordinator!.addPersistentStoreWithType(
NSSQLiteStoreType, configuration: nil, URL: url, options: mOptions)

但在我的 Xcode 8 Swift 3 项目中，我找不到 addPersistentStoreWithType 的调用位置.这是我创建项目时生成的唯一核心数据代码:

But in my Xcode 8 Swift 3 project I can't find where addPersistentStoreWithType is called. This is the only core data code that was generated when I created my project:

 // 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: "Habits")
    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)")
        }
    }
}

如何使用 Swift 3 在 Xcode 8 中启用轻量级迁移?

推荐答案

您可以使用 NSPersistentStoreDescription 来完成，这是所有这些选项在 Swift 3 中更新的地方.在调用 loadPersistentStores 之前执行此操作:

You do it using NSPersistentStoreDescription, which is where all those options moved to in the Swift 3 updates. Do this before the call to loadPersistentStores:

let description = NSPersistentStoreDescription()

description.shouldInferMappingModelAutomatically = true
description.shouldMigrateStoreAutomatically = true

container.persistentStoreDescriptions = [description]

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