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Core Data / NSPredicate - faster alternative to JOIN?

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Core Data / NSPredicate - faster alternative to JOIN?

Subject: Core Data / NSPredicate - faster alternative to JOIN?
From: Jim Correia <email@hidden>
Date: Wed, 17 May 2006 21:29:16 -0400

The predicate programming guide points out that JOINs are expensive operations and should be avoided where possible.

Suppose I have the following entities:

Student
Course

Student has a to-many relationship to course with an appropriate inverse relationship. I'd like to quickly determine which students have no courses assigned.

A fetch request for the Student entity with a predicate of "courses.@count == 0" gives me the answer I'm looking for, but it is relatively expensive. (No surprise - the docs said it would be.)

Can I write a predicate which avoids the join?

Any other way to get the result more efficiently?

Thanks,
Jim

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