Question

I have a Core Data entity, OrderItem that has a to-many relationship to another entity, OrderItemOption. I want to find a specific OrderItem that has a relationship to two specific OrderItemOptions. How do I do that in Core Data?

OrderItemOptions has a typecode and optioncode, essentially a key/value. I’m looking for an orderItem with an option (typecode=OptionSet1, optionCode=BT) and another option (typecode=OptionSet2, optionCode=CT).

The issue is how to distinguish the first OrderItemOption object and the second in the query.

I was able to come up with a SQL query to do exactly what I want. It uses aliases to perform a join the table with itself. How do I do the equivalent in Core Data?

The sql statement is:

 select * from zorderItem, zorderItemOption one, zorderItemOption two where 
 one.zorderitem = zorderItem.z_pk and 
 one.zoptiontypecode='OptionSet1' and one.zoptioncode='BT' and 
 two.zorderitem =zorderitem.z_pk and
 two.zoptiontypecode='OptionSet2' and two.zoptioncode='CT';

I don’t think I quite follow the semantics behind the ‘ANY’ keyword in predicates. I was able to get close with,

NSPredicate *pre = [NSPredicate predicateWithFormat:
            @"order == %@ and 
            (any options.optionTypeCode == %@ and any options.optionCode == %@)
            and 
            (any options.optionTypeCode == %@ and any options.optionCode == %@)",
            order, @"OptionSet1", @"BT", @"OptionSet2", @"CT"];

But it also matched when the optionCodes where reversed.

I tried factoring the ‘ANY’ outside each parenthesis expression, but that caused a parse exception.

Perhaps a simpler example would be interesting as well. What if I have an Author entity with a to-many relationship to Books. How would I create a predicate to say, find the author who has written the both the book titled “Book1” and the book titled “Book2”?

Answer 1

Someone answered on Apple developer forum, https://devforums.apple.com/message/659752#659752

Repeating post here,

It sounds like what you’re looking for is a sub-query. One of the explanations for sub queries: http://funwithobjc.tumblr.com/post/2726166818/what-the-heck-is-subquery

I think it would be something like

order == %@ AND
subquery(orderItemOptions, $one, $one.typeCode = %@ && $one.optionCode = %@).@count >0 AND
subquery(orderItemOptions, $two, $two.typeCode = %@ && $two.optionCode = %@).@count >0

for the predicate. Although I’m not sure why you had the order == %@ clause in your attempt, and I just kept it in the version with subqueries for consistency with that…