javax.persistence.MapKey - JPA annotation
javax.persistence
Annotation MapKey
- Target:
- Fields (including property get methods)
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:
- JPA 1.0
Default: If the name
element is not specified, the primary key of the associated entity is used as the map key. If the primary key is a composite primary key and is mapped as IdClass
, an instance of the primary key class is used as the key.
- Default value:
- ""
- Since:
- JPA 1.0