How it works...

We have started our example by creating two classes, Person and Dog. The Person class has one-to-many relation to the Dog class via the property array dogs. The Dog class has one-to-one relation to class Person via the property owner. Everything looks good, and it works fine if you tested, but unfortunately we did a terrible mistake. We have a retain cycle problem here, which means we have two objects in memory; each one has a strong reference to the other. This leads to a cycle that prevents both of them from being deallocated from memory.

This problem is a common problem in iOS, and not all developers note it while coding. We call it as parent-child relation. Parent (in our case, it's the Person class) should always have a strong reference to child (the Dog class); child should always have a weak reference to the parent. Child doesn't need to have strong reference to parent, as child should never exit when parent is deallocated from memory.

To solve such a problem, you have to break the cycle by marking one of these references as weak. In step 2, we see how we solved the problem by marking the property owner as weak.