Package jakarta.persistence
Annotation Type MapKey
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@Target({METHOD,FIELD}) @Retention(RUNTIME) public @interface MapKey
Specifies the map key for associations of typejava.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 whenMapKey
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() { ... } ... }
- Since:
- 1.0
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Element Detail
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name
String name
(Optional) The name of the persistent field or property of the associated entity that is used as the map key.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 asIdClass
, an instance of the primary key class is used as the key.- Default:
- ""
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