ios - 是否允许通过同一个NSManagedContext的performBlock传递NSManagedObject？

Question

我可以在同一 NSManagedContext 的不同执行 block 中设置对象之间的关系吗？

我创建了一个私有(private)上下文 并使用(仅示例):

let pContext = persistentContainer.newBackgroundContext()
pContext.perform {
   let user = pContext.fetch(<fetch Request>).first
   pContext.performAndWait {
        let book = pContext.fetch(<another fetch request>).first
        book.name = "skjkjd"
        pContext.save()
        book.author = user
        pContext.save()
   }
}

这段代码可能会产生以下错误，在什么情况下会产生错误？

Fatal Exception: NSInvalidArgumentException Illegal attempt to establish a relationship 'author' between objects in different contexts

Answer 1

如果我没记错的话，AppDelegate permanentContainer.viewContext 是一个单例。您不应该按照您尝试的方式跨线程传递 MOC。

看一下苹果文档:https://developer.apple.com/documentation/coredata/using_core_data_in_the_background

尝试(未测试):

    let pContext = persistentContainer.newBackgroundContext()
    pContext.perform {
        let user = pContext.fetch(<fetch Request>).first
        let userObjcID = user.objectID
            pContext.performAndWait {
                 let book = pContext.fetch(<another fetch request>).first
                 book.name = "skjkjd"
                 // pContext.save()
                 book.author = pContext.object(with: userObjcID)
        pContext.save()
   }
}