jakarta.persistence.MapKey

Specifies the map key for associations of type java.util.Map when the map key is itself the primary key or a persistent field or property of the entity that is the value of the map.

If a persistent field or property other than the primary key is used as a map key then it is expected to have a uniqueness constraint associated with it.

The MapKeyClass annotation is not used when MapKey is specified and vice versa.

Example 1:

@Entity
public class Department {
    ...
    @OneToMany(mappedBy = "department")
    @MapKey  // map key is primary key
    public Map getEmployees() {... }
    ...
}

@Entity
public class Employee {
    ...
    @Id
    Integer getEmpId() { ... }
    @ManyToOne
    @JoinColumn(name = "dept_id")
    public Department getDepartment() { ... }
    ...
}

Example 2:

@Entity
public class Department {
    ...
    @OneToMany(mappedBy = "department")
    @MapKey(name = "name")
    public Map getEmployees() {... }
    ...
}

@Entity
public class Employee {
    @Id
    public Integer getEmpId() { ... }
    ...
    @ManyToOne
    @JoinColumn(name = "dept_id")
    public Department getDepartment() { ... }
    ...
}

Since:

Jakarta Persistence (JPA) 1.0