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
    ...
}

This annotation is specified on the owning side of a OneToMany or ManyToMany relationship or on an element collection—and always on the side of the relationship that references the map. The map key is not visible as part of the state of the entity or embeddable class.

This annotation is used with owned collections. For unowned collections, that is, for association mappings which specify mappedBy, the MapKey annotation should be used. Use of the MapKeyColumn annotation on the unowned side of a relationship is not portable between persistence providers.

Since:
2.0

  • Optional Element Summary

    Optional Elements
    Modifier and Type
    Optional Element
    Description
    CheckConstraint[]
    check
    (Optional) Check constraints to be applied to the column.
    String
    columnDefinition
    (Optional) The SQL fragment that is used when generating the DDL for the column.
    String
    comment
    (Optional) A comment to be applied to 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

    • check

      CheckConstraint[] check
      (Optional) Check constraints to be applied to the column. These are only used if table generation is in effect.
      Since:
      4.0
      Default:
      {}

    • comment

      String comment
      (Optional) A comment to be applied to the column. This is only used if table generation is in effect.
      Since:
      4.0
      Default:
      ""