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Editorial Team
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Asked: 2026-06-03T07:39:58+00:00

I need to insert few NSManagedObject subclass instances ( Object B ) in the

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I need to insert few NSManagedObject subclass instances (Object B) in the to-many relationship of the Object A, but I don’t know if these Objects B is already exist in Object A relationship. What would happen if I will insert them? Would they be inserted twice, or Core Data wouldn’t do that?

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  1. Editorial Team

    Because the to-many relationship is accessed as a NSSet, only unique objects will be added (this is a feature of NSSet’s) so you don’t need to worry about checking to see if it is already there first.

    To quote the documentation for NSSet:

    NSSet declares the programmatic interface for static sets of distinct objects.

    and from the NSMutableSet documentation:

    addObject:

    Adds a given object to the set, if it is not already a member.

    - (void)addObject:(id)object

    Parameters

    object

    The object to add to the set.

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