Module jakarta.persistence

Package jakarta.persistence

Annotation Interface MapKeyColumn

@Target({METHOD,FIELD})
@Retention(RUNTIME)
public @interface MapKeyColumn

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<String, String> images;  // map from image name to filename
    ...
}

Since:

2.0

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element	Description
String	columnDefinition	(Optional) The SQL fragment that is used when generating the DDL for the column.
boolean	insertable	(Optional) Whether the column is included in SQL INSERT statements generated by the persistence provider.
int	length	(Optional) The column length.
String	name	(Optional) The name of the map key column.
boolean	nullable	(Optional) Whether the database column is nullable.
String	options	(Optional) A SQL fragment appended to the generated DDL which declares this column.
int	precision	(Optional) The precision for a column of SQL type decimal or numeric, or of similar database-native type.
int	scale	(Optional) The scale for a column of SQL type decimal or numeric, or of similar database-native type.
String	table	(Optional) The name of the table that contains the column.
boolean	unique	(Optional) Whether the column is a unique key.
boolean	updatable	(Optional) Whether the column is included in SQL UPDATE statements generated by the persistence provider.

Element Details

name

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".

Default:

""

unique

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.

Default:

false

nullable

boolean nullable

(Optional) Whether the database column is nullable.

Default:

false

insertable

boolean insertable

(Optional) Whether the column is included in SQL INSERT statements generated by the persistence provider.

Default:

true

updatable

boolean updatable

(Optional) Whether the column is included in SQL UPDATE statements generated by the persistence provider.

Default:

true

columnDefinition

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.

Default:

""

options

String options

(Optional) A SQL fragment appended to the generated DDL which declares this column. May not be used in conjunction with columnDefinition().

Since:

3.2

Default:

""

table

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.

Default:

""

length

int length

(Optional) The column length.

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

Default:

255

precision

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.

Default:

0

scale

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.

Default:

0