| Is used to specify the map key for associations of type
java.util.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.
Example 1:
@Entity
public class Department {
...
@OneToMany(mappedBy="department")
@MapKey(name="empId")
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="empPK")
public Map getEmployees() {... }
...
}
@Entity
public class Employee {
@EmbeddedId public EmployeePK getEmpPK() { ... }
...
@ManyToOne
@JoinColumn(name="dept_id")
public Department getDepartment() { ... }
...
}
@Embeddable
public class EmployeePK {
String name;
Date bday;
}
since:
Java Persistence 1.0 |