javax.persistence

Annotation Type MapKeyColumn

@Target(value={METHOD,FIELD})
@Retention(value=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:

Java Persistence 2.0

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and 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.
int	precision (Optional) The precision for a decimal (exact numeric) column.
int	scale (Optional) The scale for a decimal (exact numeric) column.
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 Detail

name

public abstract 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".

Returns:

The name

Default:

""

unique

public abstract 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.

Returns:

Whether unique

Default:

false

nullable

public abstract boolean nullable

(Optional) Whether the database column is nullable.

Returns:

Whether nullable

Default:

false

insertable

public abstract boolean insertable

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

Returns:

Whether insertable

Default:

true

updatable

public abstract boolean updatable

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

Returns:

Whether updateable

Default:

true

columnDefinition

public abstract 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.

Returns:

The column definition

Default:

""

table

public abstract 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.

Returns:

The table

Default:

""

length

public abstract int length

(Optional) The column length. (Applies only if a string-valued column is used.)

Returns:

The length

Default:

255

precision

public abstract int precision

(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.)

Returns:

The precision

Default:

0

scale

public abstract int scale

(Optional) The scale for a decimal (exact numeric) column. (Applies only if a decimal column is used.)

Returns:

The scale

Default:

0