2 Foreign Keys Into a New Table from Different Entities Hibernate - spring

Question

In my projecet people has role based access.One person can work at more than one departments.
My Role Table
Role_id Role
1 Manager
2 Employee
My Department Table
Departmant_id Departmant
1 Production
2 Research
3 Marketing
My User Table
User_id User_name
1 Jennifer
2 Kate
3 David
What i want is a new table that specifies which people are in which departmant and what role do they have in that department.
User_id Departmant_id Role_id
x x x
What i tried is
Class User{
#ManyToOne(cascade = CascadeType.ALL)
#JoinTable(name = "user_department_role",joinColumns = {#JoinColumn(name = "department_id",referencedColumnName = "department_id"),#JoinColumn(name = "user_id",referencedColumnName = "user_id")}, inverseJoinColumns = {#JoinColumn(name = "role_id")})
private Set<Department> departmentList;
}

Answer 1

You need an association table, often constructed in JPA for various reasons mostly to do with control over what goes in the table or in this case mapping an n-way M:N relationship.
Create all your Entities:
#Entity
public class User {
#Id #GeneratedValue(strategy=GenerationType.AUTO)
private Integer id;
private String userName;
#OneToMany(mappedBy="user")
private Set<UserDepartmentRoleAssociation> associations;
... etc
}
and
#Entity
public class Department {
#Id #GeneratedValue(strategy=GenerationType.AUTO)
private Integer id;
private String department;
#OneToMany(mappedBy="department")
private Set<UserDepartmentRoleAssociation> associations;
... etc
}
and
#Entity
public class Role {
#Id #GeneratedValue(strategy=GenerationType.AUTO)
private Integer id;
private String role;
... etc
}
and create your association table and id class.
#Entity
public class UserDepartmentRoleAssociation {
#EmbeddedId private UserDepartmentRoleAssociationId id;
#ManyToOne #MapsId("userId")
private User user;
#ManyToOne #MapsId("departmentId")
private Department department;
#ManyToOne #MapsId("roleId")
private Role role;
public UserDepartmentRoleAssociation() {
id = new UserDepartmentRoleAssociationId();
}
... etc
}
and
#Embeddable
public class UserDepartmentRoleAssociationId implements Serializable {
private Integer userId;
private Integer departmentId;
private Integer roleId;
... etc
}
and to persist a relationship then ...
User user = new User();
user.setUserName("user1");
Department department = new Department();
department.setDepartment("department 1");
Role role = new Role();
role.setRole("Manager");
UserDepartmentRoleAssociation association = new UserDepartmentRoleAssociation();
association.setUser(user);
association.setDepartment(department);
association.setRole(role);
em.persist(user);
em.persist(department);
em.persist(role);
em.persist(association);
and to read it with join fetch then
User user = em.createQuery("select u from User u left join fetch u.associations ass left join fetch ass.department left join fetch ass.role where u.id = :id", User.class).setParameter("id", 1).getSingleResult();
Note that I have used a Set instead of a List in Department and User which causes much less problems in these cases. Also, I don't have to create associations when I persist the relationship because the UserDepartmentRoleAssociation is the owning entity and therefore does the persisting. The associations sets are created by JPA when it reads a record.