javax.persistence

Annotation Type JoinColumn

@Target(value={METHOD,FIELD})
@Retention(value=RUNTIME)
public @interface JoinColumn

Specifies a column for joining an entity association or element collection. If the JoinColumn annotation itself is defaulted, a single join column is assumed and the default values apply.

   Example:

   @ManyToOne
   @JoinColumn(name="ADDR_ID")
   public Address getAddress() { return address; }


   Example: unidirectional one-to-many association using a foreign key mapping

   // In Customer class
   @OneToMany
   @JoinColumn(name="CUST_ID") // join column is in table for Order
   public Set<Order> getOrders() {return orders;}
 

Since:

Java Persistence 1.0

See Also:

ManyToOne, OneToMany, OneToOne, JoinTable, CollectionTable

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
java.lang.String	columnDefinition (Optional) The SQL fragment that is used when generating the DDL for the column.
ForeignKey	foreignKey (Optional) The foreign key constraint specification for the join column.
boolean	insertable (Optional) Whether the column is included in SQL INSERT statements generated by the persistence provider.
java.lang.String	name (Optional) The name of the foreign key column.
boolean	nullable (Optional) Whether the foreign key column is nullable.
java.lang.String	referencedColumnName (Optional) The name of the column referenced by this foreign key column.
java.lang.String	table (Optional) The name of the table that contains the column.
boolean	unique (Optional) Whether the property 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 java.lang.String name

(Optional) The name of the foreign key column. The table in which it is found depends upon the context.

• If the join is for a OneToOne or ManyToOne mapping using a foreign key mapping strategy, the foreign key column is in the table of the source entity or embeddable.
• If the join is for a unidirectional OneToMany mapping using a foreign key mapping strategy, the foreign key is in the table of the target entity.
• If the join is for a ManyToMany mapping or for a OneToOne or bidirectional ManyToOne/OneToMany mapping using a join table, the foreign key is in a join table.
• If the join is for an element collection, the foreign key is in a collection table.

Default (only applies if a single join column is used): The concatenation of the following: the name of the referencing relationship property or field of the referencing entity or embeddable class; "_"; the name of the referenced primary key column. If there is no such referencing relationship property or field in the entity, or if the join is for an element collection, the join column name is formed as the concatenation of the following: the name of the entity; "_"; the name of the referenced primary key column.

Default:

""

referencedColumnName

public abstract java.lang.String referencedColumnName

(Optional) The name of the column referenced by this foreign key column.

• When used with entity relationship mappings other than the cases described here, the referenced column is in the table of the target entity.
• When used with a unidirectional OneToMany foreign key mapping, the referenced column is in the table of the source entity.
• When used inside a JoinTable annotation, the referenced key column is in the entity table of the owning entity, or inverse entity if the join is part of the inverse join definition.
• When used in a CollectionTable mapping, the referenced column is in the table of the entity containing the collection.

Default (only applies if single join column is being used): The same name as the primary key column of the referenced table.

Default:

""

unique

public abstract boolean unique

(Optional) Whether the property 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 is only a single field. It is not necessary to explicitly specify this for a join column that corresponds to a primary key that is part of a foreign key.

Default:

false

nullable

public abstract boolean nullable

(Optional) Whether the foreign key column is nullable.

Default:

true

insertable

public abstract boolean insertable

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

Default:

true

updatable

public abstract boolean updatable

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

Default:

true

columnDefinition

public abstract java.lang.String columnDefinition

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

Defaults to the generated SQL for the column.

Default:

""

table

public abstract java.lang.String table

(Optional) The name of the table that contains the column. If a table is not specified, the column is assumed to be in the primary table of the applicable entity.

Default:

• If the join is for a OneToOne or ManyToOne mapping using a foreign key mapping strategy, the name of the table of the source entity or embeddable.
• If the join is for a unidirectional OneToMany mapping using a foreign key mapping strategy, the name of the table of the target entity.
• If the join is for a ManyToMany mapping or for a OneToOne or bidirectional ManyToOne/OneToMany mapping using a join table, the name of the join table.
• If the join is for an element collection, the name of the collection table.

Default:

""

foreignKey

public abstract ForeignKey foreignKey

(Optional) The foreign key constraint specification for the join column. This is used only if table generation is in effect. Default is provider defined.

Returns:

The foreign key specification

Default:

@javax.persistence.ForeignKey