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swiftcore-data

Swift Core Data Usage in Xcode

I am relatively new to Swift Programming and recently tried out Core Data for the first time. However, I am having a hard time understanding several (for me) strange behaviours I am encountering:

  • I have create all my entities and their attributes in the ".xcdatamodeld" file. Codegen is on "Manual/None". Some of the attributes are marked a non-optional. Still, when I generate the NSManagedObject Subclass files, I still see them as optional in the "...Properties" files, i.e. having a "?" after the type. Why is that?
  • Somewhat relating/in contrast to the first bullets, the attributes for some entities do not have the "?", although they are marked as optional. When I try to add the "?", I get an error "Property cannot be marked @NSManaged because its type cannot be represented in Objective-C". Why is that?
  • When I'm creating the NSManagedObject Subclasses and select some subfolder in my project for them to be created in, they are put at the top of the hierarchy tree, regardless.
  • What happens if I change information in the "...Class"/"...Properties" files generated by Core Data which would conflict with what is in the ".xcdatamodeld" file. What takes precedence? How are they related?

In general I find there is not much detailed descriptions available on Core Data except introductory things. Would anyone know some good resources on that? Website? Youtube Videos? Books?

Solution

  • Answers:

    • Creating the subclasses manually treates the optionals not accurately. Check any attribute and remove the question mark in the class if it's non-optional in the model.

    • Scalar Swift optional types (Int?, Double?, Bool?) cannot be represented in Objective-C. I recommend to declare them as non-optional.

    • Never mind, it has no effect where the classes are located, the main thing is that the file name is black (valid) in the Project Navigator and the target membership is assigned correctly.

    • in the Codegen Manual / None case you are responsible that the types in the model match the types in the classes otherwise you could get unexpected behavior. Any change in the class must be done also in the model and vice versa. However you can replace suggested ObjC classes like NSSet or NSDate with native Swift types Set<MyClass> or Date without changing the type in the model.