Xcode NSManagedObject 子类在标记为非可选时包含可选

Question

I have a core data entity named Film which has properties title and date. I noticed that the generated NSManagedObject subclass contains optional NSManaged properties even though I marked the properties as non optional in the core data inspector.

Can I can manually change it as non-optional property or is it a better choice to leave it as optional? Why?

Answer 1

"Optional" means something different to Core Data than it does to Swift.

• 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 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.

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.

Answer 2

This is a known issue. Some people change it to non-optional with no adverse effects, I keep it the way it was generated and hope for early fix.

It always helps if you submit a bug to Apple to increase visibility and priority.

Answer 3

Create managedobject class and change the entity class type to manual and add these classes to your project scope.

Edit your managedObject to make them non-optional. This means you need to maintain this class yourself and do any changes both in the core data model and the class

If your data model is stable and won't be changed then you can use this.

Answer 4

The Optional checkbox in the data model inspector has nothing to do with Swift optionals. The checkbox determines whether or not the attribute is required to have a value.

If you deselect the Optional checkbox for an attribute, you must give that attribute a value or you will get an error when saving. By selecting the Optional checkbox you can save without giving the attribute a value. Suppose you have a description attribute that's a string. If you select the Optional checkbox you could leave the description blank and still save the entity.

Here's another example. Suppose you have text fields to let a person enter their home, work, and cell phone numbers. These phone numbers should be optional attributes. You wouldn't want to require someone to have a home phone number, a work phone number, and a cell phone number just to save the person's data.