Fixing the Mysteriously Missing Core Data Objects

The below post helps you to identify and fix the mysteriously missing Core Data objects. I have also provided a link with a working project where I demonstrate how objects go missing and how it can be fixed.

Checklist for the solution below

• You are getting <x-coredata: UDID; data: fault>, despite setting fetchRequest.returnsObjectsAsFaults = false and saving the managed object context properly
• Your objects and relationships are available on first run and go missing once you restart/relaunch the app — or sometimes a few objects and relationships are randomly available and start missing in subsequent runs
• You don’t have any other errors while saving the managed object context
• The objects are missing where you don’t have an inverse relationship, and Xcode is also indicating a warning about the missing inverse relationship

When Does It Happen

Most cases follow a similar pattern. Check if it suits your situation:

• A has a one-to-many relationship with B. B doesn’t have any inverse relationship.
• B’s objects are inserted first and saved to the store.
• A’s objects are created in context, B’s objects are fetched and mapped to A.
• When you save the context, it appears A is saved along with its relationship to B’s objects.
• But when you fetch immediately from the store, A’s relationship to B is missing and you cannot access B’s objects from A.

Solution

There are 2 solutions:

1. B should have an inverse relationship to A. (Recommended if possible.)

   (or)

2. Ensure that A’s object is first saved to the store as soon as it’s created.

   • Now fetch A’s object, map it to existing B objects, and save it to the store.
   • When you fetch/refresh A’s object, you will be able to access B’s objects despite not having an inverse relationship.

Projects in This Repo

There are 2 projects in my repo to demonstrate the above solution:

1. OneToMany-NotWorking — demonstrates why it’s not working
2. OneToMany-Working — demonstrates how to make it work

Citation

Please provide citation to this repo in Stack Overflow or wherever required.