Core data many to many relationship query

Question

Suppose two entities: EntityA and EntityB, connected by many to many relationship. Suppose the relation attributes are relatedEntityBs and relatedEntityAs respectively. And I have an NSArray of EntityB instances. I want to find all EntityA instances which have in relation all instances that are in nsarray. That is if the array is [entityB1,.....,entityBn]. Find all EntityA instances, which are related with entityB1,wntityB2 till entityBn. How can I write this kind of predicate?

Do you want to check for equality, i.e. find all objects that are related to entityB1, ..., entitiyBn and no others? Then this might be useful: stackoverflow.com/questions/13084930/…. — Martin R

Rakesh Rakesh · Accepted Answer · 2013-03-07T19:53:16

This predicate should do it:

NSMutablArray *predicateArray = [NSMutableArray array];
for (int i=0;i<entityBArray.count;i++){
     NSPredicate *subPredicate = [NSPredicate predicateWithFormat:@"ANY relatedEntityBs contains %@",[entityBArray objectAtIndex:i];
     [predicateArray addObject:subPredicate] ;
} 
NSCompoundPredicate *daddyPredicate = [NSCompoundPredicate orPredicateWithSubpredicates:predicateArray];

Basically each sub predicate checks if relatedEntityB contains a single object of the array and finally the daddyPredicate combines them all in with OR.

Core data many to many relationship query

1 Answers