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

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.