SUBQUERY in NSPredicate and NSInvalidArgumentException

Question

I set up the following model in Core Data.

Book has a to-many relationship, called toBookOrders, with OrderBook entity. The inverse is called toBook.
Book ha         


        

Answer 1

Separate the isSync == 0 and SUBQUERY into separate NSPredicates, add them to an NSArray then use [NSCompoundPredicate andPredicateWithSubpredicates:array] to get them joined into a single one to pass to your NSFetchSpecification.

Answer 2

Here's the crux of your problem:

@"isSync == 0 AND SUBQUERY(toBookOrders, $x, $x.toBook == SELF)"

If you split that up into the two subpredicates, as Scott suggests, you'll get:

• isSync == 0
• SUBQUERY(toBookOrders, $x, $x.toBook == SELF)

The problem is that every SUBQUERY does not return true or false, as a predicate must. It returns a collection (an array), and an array is not the same thing as true or false. Thus, when you create the predicate, you're getting an error that it's an invalid format, because the stuff after the AND isn't a predicate. It's simply an expression.

You're probably wanting:

@"isSync == 0 AND SUBQUERY(toBookOrders, $x, $x.toBook == SELF).@count > 0"

This would give you a predicate to find all the books where isSync is false and the at least one of the Book's OrderBooks is that Book.