CODEWITHSUNDEEP
objective-ccore-datarelationshipnsfetchrequest
krata
krata

Reputation: 101

NSFetchRequest - get all objects by relationship

It's possible create aNSFetcherRequest or something similar for get all objects by relationship? For example I have three entities student, absence and subject. Student has attributes NSSet absence, absence has attribute student and subject. I need get all absence of one student and one subject. So I need require similar this pseudo code: select all absence where student=="concrete student" and where subject=="concrete subject". But it aren't attributes, but relationship! How can I do it? I know, that I can get all absence of student and than filter it, but I think, its very inefficient.

Upvotes: 0

Views: 568

Answers (1)

Martin R
Martin R

Reputation: 539685

Both attributes and relationships are properties of a managed object and can be used as key path in a predicate, for example:

 Student *concreteStudent = ...;
 Subject *concreteSubject = ...;
 NSPredicate *predicate = [NSPredicate predicateWithFormat:@"student = %@ AND subject = %@",
     concreteStudent, concreteSubject];
 NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Absence"];
 fetchRequest.predicate = predicate;

if "student" and "subject" are to-one relationships of the Absence entity.

Upvotes: 1

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