composite primary key which contains a foreign key - jpa

Question

I have an entity called UserWithRoles:
#Entity
#Getter
#Setter
public class UserWithRoles implements Serializable
{
#Id
#GeneratedValue( strategy = GenerationType.AUTO )
private int id;
private String name;
private String password;
#OneToMany( mappedBy = "user" )
private List<UserRole> roles;
}
A UserRole entity:
#Entity
#Getter
#Setter
#IdClass( UserRolePK.class )
#Inheritance( strategy = InheritanceType.JOINED )
#DiscriminatorColumn( name = "roleType", discriminatorType = DiscriminatorType.STRING, length = 10 )
abstract public class UserRole implements Serializable
{
#Id
// It should be mapped as a foreign PK by user.id (user field declared below)
private int userID;
#Id
private String roleType;
#ManyToOne
#JoinColumn( name="user_id", referencedColumnName = "id" )
private UserWithRoles user;
}
The primary key class UserRolePK:
#Data
public class UserRolePK implements Serializable
{
private int userID;
private String roleType;
}
I want to create a composite PK to UserRole: UserWithRoles.id + UserRole.roleType
How can I map it to the database? Should I use the UserWithRoles type in the PK class instead of the ID? Is it a good idea at all? Or I just should use normal PK to UserRole? The relation would be something like that between the ClientOrder and ClientOrdetItem entities: (ClientOrder.id + ClientOrderItem.num)

Answer 1

You are using Derived Identity.
You need to change UserRole to look like this:
#Entity
#Getter
#Setter
#IdClass( UserRolePK.class )
#Inheritance( strategy = InheritanceType.JOINED )
#DiscriminatorColumn( name = "roleType", discriminatorType = DiscriminatorType.STRING, length = 10 )
abstract public class UserRole implements Serializable
{
#Id
private String roleType;
#Id
#ManyToOne
#JoinColumn( name="user_id", referencedColumnName = "id" )
private UserWithRoles user;
}
That is, get rid of the userID field and add an #Id annotation to the user field.
And change UserRolePK to look like this:
#Data
public class UserRolePK implements Serializable
{
private int user;
private String roleType;
}
That is, change the name of the userID field to user, to match the name of the #Id field in UserRole (but its type must still match the type of the UserWithRoles PK field, id).
Derived identity is discussed in JPA 2.1 spec, section 2.4.1.