Jakarta Persistence (JPA) Annotation Type

jakarta.persistence.MapKeyColumn

Implemented Interfaces:
Annotation
Target:
Method, Field
Specifies the mapping for the key column of a map whose map key is a basic type. If the name element is not specified, it defaults to the concatenation of the following: the name of the referencing relationship field or property; "_"; "KEY".

Example: 

@Entity
public class Item {
    @Id
    int id;
    ...
    @ElementCollection
    @MapKeyColumn(name = "IMAGE_NAME")
    @Column(name = "IMAGE_FILENAME")
    @CollectionTable(name = "IMAGE_MAPPING")
    Map images;  // map from image name to filename
    ...
}

Since:
Jakarta Persistence (JPA) 2.0

Public Instance Methods

String columnDefinition()
(Optional) The SQL fragment that is used when generating the DDL for the column.

Defaults to the generated SQL to create a column of the inferred type.

Since:
Jakarta Persistence (JPA) 1.0
boolean insertable()
(Optional) Whether the column is included in SQL INSERT statements generated by the persistence provider.
Since:
Jakarta Persistence (JPA) 1.0
int length()
(Optional) The column length.

Applies only to columns whose type is parameterized by length, for example, varchar or varbinary types.

Since:
Jakarta Persistence (JPA) 1.0
String name()
(Optional) The name of the map key column.
The table in which it is found depends upon the context.
  • If the map key is for an element collection, the map key column is in the collection table for the map value.
  • If the map key is for a ManyToMany entity relationship or for a OneToMany entity relationship using a join table, the map key column is in a join table.
  • If the map key is for a OneToMany entity relationship using a foreign key mapping strategy, the map key column is in the table of the entity that is the value of the map.

Defaults to the concatenation of the following: the name of the referencing relationship field or property; "_"; "KEY".

Since:
Jakarta Persistence (JPA) 1.0
boolean nullable()
(Optional) Whether the database column is nullable.
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.
Since:
Jakarta Persistence (JPA) 3.2
int precision()
(Optional) The precision for a column of SQL type decimal or numeric, or of similar database-native type.

Applies only to columns of exact numeric type.

The default value 0 indicates that a provider-determined precision should be inferred.

Since:
Jakarta Persistence (JPA) 1.0
int scale()
(Optional) The scale for a column of SQL type decimal or numeric, or of similar database-native type.

Applies only to columns of exact numeric type.

The default value 0 indicates that a provider-determined precision should be inferred.

Since:
Jakarta Persistence (JPA) 1.0
String table()
(Optional) The name of the table that contains the column.

Defaults: If the map key is for an element collection, the name of the collection table for the map value. If the map key is for a OneToMany or ManyToMany entity relationship using a join table, the name of the join table for the map. If the map key 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.

Since:
Jakarta Persistence (JPA) 1.0
boolean unique()
(Optional) Whether the column 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 corresponds to only a single column. This constraint applies in addition to any constraint entailed by primary key mapping and to constraints specified at the table level.
Since:
Jakarta Persistence (JPA) 1.0
boolean updatable()
(Optional) Whether the column is included in SQL UPDATE statements generated by the persistence provider.
Since:
Jakarta Persistence (JPA) 1.0

Annotation Elements

This is a marker annotation with no members/elements.

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

java.lang.annotation.Annotation/annotationType(), java.lang.annotation.Annotation/equals(Object), java.lang.annotation.Annotation/hashCode(), java.lang.annotation.Annotation/toString()