Fetch all children of parents in Core Data using predicate

Question

I have a data model relationship of Person - Children in Core Data. So for example, A Person can have children and his children can have children, and so his children's children can have children and so on.

How would I be able to fetch all the children, grand children and grand grand children using a predicate?

And are `Child` and `Person` different entities? Or is `children` a reflexive relationship from `Person` to `Person`? — pbasdf, Aug 29 '17 at 09:05
@ParagBafna Unfortunately I did not find an easy way to do this using a predicate. But you have to go thru or scan your objects for children to get them. — SleepNot, Feb 18 '18 at 06:43
I have decided to use parent child relationship to avoid looping. But it's not working https://stackoverflow.com/questions/48837975/folder-structure-in-core-data — Parag Bafna, Feb 18 '18 at 10:25

score 1 · Answer 1 · answered Aug 29 '17 at 09:14

1

If you have a Person object, thePerson, then to fetch their children you would use the following predicate:

NSPredicate(format:"parent == %@", thePerson)

To fetch their grandchildren, use:

NSPredicate(format:"parent.parent == %@", thePerson)

and for their great-grandchildren, use:

NSPredicate(format:"parent.parent.parent == %@", thePerson)

Combine those together:

NSPredicate(format:"parent == %@ OR parent.parent == %@ OR parent.parent.parent == %@", thePerson, thePerson, thePerson)

answered Aug 29 '17 at 09:14

pbasdf

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Thanks for the answer. And pardon me if I used a "fixed" example in my question. But what if I do not know the number of levels to get the outmost children. – SleepNot Aug 29 '17 at 09:18
I was afraid you might want that. I think you might need to change your model - but I will have to think through how best to change it. – pbasdf Aug 29 '17 at 09:27

Fetch all children of parents in Core Data using predicate

1 Answers1