@Target(value={METHOD,FIELD})
@Retention(value=RUNTIME)
public @interface MapKey
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<Integer, Employee> 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<String, Employee> getEmployees() {... }
...
}
@Entity
public class Employee {
@Id public Integer getEmpId() { ... }
...
@ManyToOne
@JoinColumn(name="dept_id")
public Department getDepartment() { ... }
...
}
| Modifier and Type | Optional Element and Description |
|---|---|
java.lang.String |
name
(Optional) The name of the persistent field or property of the
associated entity that is used as the map key.
|
public abstract java.lang.String name
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.