Note: This ORM/SQL annotation is silently ignored by ObjectDB

633 words

javax.persistence.MapKeyColumn - JPA annotation

javax.persistence
Annotation MapKeyColumn

Target:
Fields (including property get methods)
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:
JPA 2.0
(Optional) The SQL fragment that is used when generating the DDL for the column.
(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 value:
""
Since:
JPA 2.0
boolean insertable
(Optional) Whether the column is included in SQL INSERT statements generated by the persistence provider.
(Optional) Whether the column is included in SQL INSERT statements generated by the persistence provider.
Default value:
true
Since:
JPA 2.0
int length
(Optional) The column length.
(Optional) The column length. (Applies only if a string-valued column is used.)
Default value:
255
Since:
JPA 2.0
String name
(Optional) The name of the map key column.
(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 value:
""
Since:
JPA 2.0
boolean nullable
(Optional) Whether the database column is nullable.
(Optional) Whether the database column is nullable.
Default value:
false
Since:
JPA 2.0
(Optional) The precision for a decimal (exact numeric) column.
(Optional) The precision for a decimal (exact numeric) column. (Applies only if a decimal column is used.)

Default: 0. (The value must be set by the developer.)

Default value:
0
Since:
JPA 2.0
int scale
(Optional) The scale for a decimal (exact numeric) column.
(Optional) The scale for a decimal (exact numeric) column. (Applies only if a decimal column is used.)
Default value:
0
Since:
JPA 2.0
String table
(Optional) The name of the table that contains the column.
(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 value:
""
Since:
JPA 2.0
boolean unique
(Optional) Whether the column is a unique key.
(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 value:
false
Since:
JPA 2.0
boolean updatable
(Optional) Whether the column is included in SQL UPDATE statements generated by the persistence provider.
(Optional) Whether the column is included in SQL UPDATE statements generated by the persistence provider.
Default value:
true
Since:
JPA 2.0

This documentation page is derived (with some adjustments) from the open source JPA 2 RI (EclipseLink)
and is available under the terms of the Eclipse Public License, v. 1.0 and Eclipse Distribution License, v. 1.0.
Object Relational Mapping (ORM) JPA 2 providers include Hibernate, EclipseLink, TopLink, OpenJPA and DataNucleus.
Object DB is not an ORM JPA implementation but an Object Database for Java with built in JPA 2 support.