为什么Xcode生成的NSManagedObject子类总是包含可选属性，即使它们被标记为非可选属性？ [英] Why Xcode generated NSManagedObject Subclass contains always optional properties even if they are marked as non-optional?
问题描述
我有一个名为Film的核心数据实体，并具有属性标题和日期。我注意到生成的NSManagedObject子类生成可选的NSManaged属性，即使我在核心数据检查器中标记为非可选。
I have a core data entity named Film and has a properties title and date. I noticed that the generated NSManagedObject subclass generate optional NSManaged property even if I marked like non optional in core data inspector.
我可以手动将其更改为非可选属性，或者是更好的选择将其作为可选属性？为什么？
I can manually change it as non-optional property or is a better choice to left it as optional? Why?
推荐答案
可选是指与Core Data不同的内容，而不是Swift。
"Optional" means something different to Core Data than it does to Swift.
- 如果Core Data属性不是可选的，则在保存更改时必须具有非零值。在其他时候，Core Data不知道或关心属性是否为nil。
- 如果Swift属性不是可选的，则它必须始终具有非nil值 。初始化完成后。
- If a Core Data attribute is not optional, it must have a non-nil value when you save changes. At other times Core Data doesn't know or care if the attribute is nil.
- If a Swift property is not optional, it must have a non-nil value at all times after initialization is complete.
使Core Data属性为非可选属性并不意味着迅速的感觉的术语。这就是为什么生成代码使这些属性是可选的 - 就Core Data而言，除非保存更改，否则使用nil值是合法的。
Making a Core Data attribute non-optional does not imply that it's non-optional in the Swift sense of the term. That's why generated code makes these properties optional-- as far as Core Data is concerned, it's legal to have nil values except when saving changes.
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