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Editorial Team
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Asked: 2026-05-28T20:06:09+00:00

I have two entities, one called Group and the other called Contact . They

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I have two entities, one called Group and the other called Contact. They have a many-to-many relationship (with a minimum of one). Thus, at least one contact can belong to one or many groups and at least one group can belong to one or many contacts.

Contact <<-->> Group

Now when I want to update a group I have in my view controller my subclassed NSManagedObject Group available. (@property (nonatomic, strong) Group *selectedGroup;)

Say if group at first has a relationship with 3 contacts, after I updated that group it should have 2 contacts (1 of the original contacts and 1 new contact).

Before update    After Update
Group            Group
-----            -----
ContactA         ContactA
ContactB         ContactD
ContactC

ContactA should stay intact.

This means that ContactB relationship should be removed from the Group (and also should be deleted from the Contact entity since no other group has a relationship with ContactB)

ContactC should be created.

How would I handle this scenario? I can’t get it to work.

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1 Answer

  1. Editorial Team

    Did you generate model classes for your core data models? If so you should have CoreDataGeneratedAccessors created that look like this in your Group class:

    - (void)addContactObject:(Contact *)value;
- (void)removeContactObject:(Contact *)value;

    You could then do the following:

    Group *group = ...
Contact *contactB = ...
Contact *contactC = ...
Contact *contactD = ...
[group addContactObject:contactD];
[group removeContactObject:contactB];
[group removeContactObject:contactC];
//save your context
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