JPA OneToOne and ManyToMany between two entities

Question

I asked a question earlier, but think it wasn\'t clear enough i will elaborate further with the code.
I have a Teacher entity and Department entity
Many Teachers

Answer 1

I removed the @oneToOne relationship between Teacher and Department and created a new entity called DepartmentHeads, everything now works fine.
Here is the Results.

@Entity
public class Teacher extends Model {
    @Required
    public String surname;

    @Required
    public String othernames;

    ... 

    @ManyToOne(cascade=CascadeType.ALL)
    public Department dept = new Department();

    ... 
}

@Entity
public class Department extends Model {
    @Required
    public String deptName; 

    @OneToMany(mappedBy="dept")
    public List<Teacher> teachers = new ArrayList<Teacher>();

    ...

}

@Entity
public class DepartmentHead extends Model{
    @OneToOne
    public Teacher teacher = new Teacher();

    @OneToOne
    public Department dept = new Department();  
}

Everything now works fine.

Answer 2

This is not a JPA problem, but is caused by recursive instantiation of Teacher/Department.

When you create, or ask JPA to create, an instance of Teacher, the Teacher attempts to instantiate a Department, which instantiates a Teacher ..., to infinity.

Hence you're seeing a StackOverflowError error near the end of that stack trace.

Remove the = new Teacher() and = new Department() expressions from the class definition; depend on and use appropriate setter methods when you create them.