Core Data structure between to-many relationship

Question

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Does every Core Data Relationship have to have an Inverse?

I am following the Core Data tutorial by Ray Wenderlich.

In his example he sets up two entities and creates a one-to-one relationship between them. He then states:

Apple recommends that whenever you create a link from one object to another, you create a link from the other object going back as well.

My question is, if I create EntityA that has a to-many relationship to EntityB, do I need to link back from EntityB to EntityA?

Look into http://stackoverflow.com/questions/764125/does-every-core-data-relationship-have-to-have-an-inverse — coverback, Aug 01 '12 at 05:25
@coverback I apologize for the duplicate post. I had been searching and searching and could never find a straight forward answer. (and yes, I did google it and a simple google search didn't bring anything up :P). — random, Aug 01 '12 at 07:08

score 1 · Accepted Answer · answered Aug 01 '12 at 05:21

1

Well, I was having a bit of a brain fart but I found my answer.

The answer is YES! You do have to set a link going back (inverse).

Here is what my model looked like before setting the links back:

enter image description here

After setting the links back it looks a bit cleaner:

enter image description here

Here is what the inspector settings look like if anyone else is having the same problem:

enter image description here

answered Aug 01 '12 at 05:21

random

If you found your answer and are satisfied with it, then you should accept it yourself. – coverback Aug 01 '12 at 05:25
@coverback Says I have to wait 2 days :/ – random Aug 01 '12 at 07:06

score 1 · Answer 2 · answered Aug 01 '12 at 05:23

1

Yes, for the sake of data integrity all of your relationships should have an inverse relationship.

answered Aug 01 '12 at 05:23

Michael Frederick

What would be the worst case scenario if a set of entities didn't have an inverse relationship set? – random Aug 01 '12 at 05:35
Data loss would be worst case I believe. For example, when inverse relationships aren't set I have seen data loss when doing an auto migration to a newer version of a core data DB. – Michael Frederick Aug 01 '12 at 06:54
Of course data loss would the worst case! haha The second part of your answer was that I was looking for. Thank you very much +1 – random Aug 01 '12 at 06:59

2 Answers2