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package javax.persistence;

import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * 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;}
 * 
 * 
 * @see ManyToOne
 * @see OneToMany
 * @see OneToOne
 * @see JoinTable
 * @see CollectionTable
 * 
 * @since Java Persistence 1.0
 */
@Target({ METHOD, FIELD })
@Retention(RUNTIME)
public @interface JoinColumn {

	/**
	 * (Optional) The SQL fragment that is used when generating the DDL for the column.
	 * 
	 * Defaults to the generated SQL for the column.
	 */
	String columnDefinition() default "";

	/**
	 * (Optional) Whether the column is included in SQL INSERT statements generated by the persistence provider.
	 * 
	 */
	boolean insertable() default true;

	/**
	 * (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.
	 */
	String name() default "";

	/**
	 * (Optional) Whether the foreign key column is nullable.
	 * 
	 **/
	boolean nullable() default true;

	/**
	 * (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.
	 */
	String referencedColumnName() default "";

	/**
	 * (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.
	 * 
	 */
	String table() default "";

	/**
	 * (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.
	 */
	boolean unique() default false;

	/**
	 * (Optional) Whether the column is included in SQL UPDATE statements generated by the persistence provider.
	 * 
	 */
	boolean updatable() default true;
}