I have a to-many relationship in my data model, and I'd like to get all the objects that have no corresponding objects in the relationship. For example: Customer - Purchases I want to get all Customers that have 0 Purchases. I've read somewhere that I could use "Purchases[SIZE] = 0", but this gives me an unsupported function expression error, which I think means it doesn't work with a SQLite backing store (which I don't want to switch from, due to some performance constraints). Any ideas?