Question

I have a problem with Core Data. The problem happens with this scenario :

-I have two entities, for instance "Department" and "Employee". 
-A to-many relationship from "Department" to "Employee"

When I generate the model, two classes are generated : “Department” and “Employee”. The “Department” class has an “NSSet” of employee thank’s to the to-many relation.

In the code, I create two instance of “Department” (d1, d2) and one of “Employee” (e1).
I would like that e1 instance could be in both d1 and d2 (via the relationship). So I do something like :

[d1 addEmployeeObject:e1 ];
[d2 addEmployeeObject:e1 ];

The problem is that, when I restart the application, e1 is no more in d1 (only in d2). It seems core-data automatically removed e1 from d1. But I don’t want that !!!

According to the core-data documentation, it seems that it is the appropriate behavior ( read Manipulating Relationships and Object Graph Integrity chapter in the link above).

How can I prevent this behavior ?? Any Idea ?

Thanks for reading,
really hope I have been clear.

Answer 1

Make an inverse relationship called Departments, a to-many from Employee to Department.

Mark the inverse of “Departments” as “Employees” where “Employees” is the to-many from Department to Employee.

When you generate the classes you should see that Department has an NSSet *employees and Employee has an NSSet *departments.