Jakarta Persistence (JPA) Annotation Type

jakarta.persistence.MapKeyJoinColumn

Implemented Interfaces:
Annotation
Target:
Method, Field
Specifies a mapping to an entity that is a map key. The map key join column is in the collection table, join table, or table of the target entity that is used to represent the map. If no MapKeyJoinColumn annotation is specified, a single join column is assumed and the default values apply.

Example 1: 

 @Entity
 public class Company {
     @Id
     int id;
     ...
     @OneToMany   // unidirectional
     @JoinTable(name = "COMPANY_ORGANIZATION",
                joinColumns = @JoinColumn(name = "COMPANY"),
                inverseJoinColumns = @JoinColumn(name = "VICEPRESIDENT"))
     @MapKeyJoinColumn(name = "DIVISION")
     Map organization;
 }

Example 2: 

 @Entity
 public class VideoStore {
     @Id
     int id;
     String name;
     Address location;
     ...
     @ElementCollection
     @CollectionTable(name = "INVENTORY",
                      joinColumns = @JoinColumn(name = "STORE"))
     @Column(name = "COPIES_IN_STOCK")
     @MapKeyJoinColumn(name = "MOVIE", referencedColumnName = "ID")
     Map videoInventory;
     ...
 }

 @Entity
 public class Movie {
     @Id long id;
     String title;
     ...
 }

Example 3: 

 @Entity
 public class Student {
     @Id
     int studentId;
     ...
     @ManyToMany  // students and courses are also many-many
     @JoinTable(name = "ENROLLMENTS",
                joinColumns = @JoinColumn(name = "STUDENT"),
                inverseJoinColumns = @JoinColumn(name = "SEMESTER"))
     @MapKeyJoinColumn(name = "COURSE")
     Map enrollment;
     ...
 }
See Also:
Since:
Jakarta Persistence (JPA) 2.0

Annotation Elements

String name
(Optional) The name of the foreign key column for the map key.
The table in which it is found depends upon the context.
  • If the join is for a map key for an element collection, the foreign key column is in the collection table for the map value.
  • If the join is for a map key for a ManyToMany entity relationship or for a OneToMany entity relationship using a join table, the foreign key column is in a join table.
  • If the join is for a OneToMany entity relationship using a foreign key mapping strategy, the foreign key column for the map key is in the table of the entity that is the value of the map.

Default (only applies if a single join column is used.) The concatenation of the following: the name of the referencing relationship property or field of the referencing entity or embeddable class; "_"; "KEY".

Default:
""
Since:
Jakarta Persistence (JPA) 1.0
String referencedColumnName
(Optional) The name of the column referenced by this foreign key column.
The referenced column is in the table of the target entity.

Default (only applies if single join column is being used.) The same name as the primary key column of the referenced table.

Default:
""
Since:
Jakarta Persistence (JPA) 1.0
boolean unique
(Optional) Whether the property is a unique key.
This is a shortcut for the UniqueConstraint annotation at the table level and is useful for when the unique key constraint is only a single field.
Default:
false
Since:
Jakarta Persistence (JPA) 1.0
boolean nullable
(Optional) Whether the foreign key column is nullable.
Default:
false
Since:
Jakarta Persistence (JPA) 1.0
boolean insertable
(Optional) Whether the column is included in SQL INSERT statements generated by the persistence provider.
Default:
true
Since:
Jakarta Persistence (JPA) 1.0
boolean updatable
(Optional) Whether the column is included in SQL UPDATE statements generated by the persistence provider.
Default:
true
Since:
Jakarta Persistence (JPA) 1.0
String columnDefinition
(Optional) The SQL fragment that is used when generating the DDL for the column.
Defaults to SQL generated by the provider for the column.
Default:
""
Since:
Jakarta Persistence (JPA) 1.0
String options
(Optional) A SQL fragment appended to the generated DDL which declares this column.
May not be used in conjunction with columnDefinition.
Default:
""
Since:
Jakarta Persistence (JPA) 3.2
String table
(Optional) The name of the table that contains the foreign key column.
  • If the join is for a map key for an element collection, the foreign key column is in the collection table for the map value.
  • If the join is for a map key for a ManyToMany entity relationship or for a OneToMany entity relationship using a join table, the foreign key column is in a join table.
  • If the join is for a OneToMany entity relationship using a foreign key mapping strategy, the foreign key column for the map key is in the table of the entity that is the value of the map.

Default:

  • If the map is for an element collection, the name of the collection table for the map value.
  • If the map is for a OneToMany or ManyToMany entity relationship using a join table, the name of the join table for the map.
  • If the map is for a OneToMany entity relationship using a foreign key mapping strategy, the name of the primary table of the entity that is the value of the map.
Default:
""
Since:
Jakarta Persistence (JPA) 1.0
ForeignKey foreignKey
(Optional) Used to specify or control the generation of a foreign key constraint when table generation is in effect.
If this element is not specified, a default foreign key strategy is selected by the persistence provider.
Default:
@ForeignKey(ConstraintMode.PROVIDER_DEFAULT)
Since:
Jakarta Persistence (JPA) 2.1

Additional JDK methods inherited from java.lang.annotation.Annotation

annotationType(), equals(Object), hashCode(), toString()