src/javax/persistence/MapKeyColumn.java

/*
 * Copyright (c) 2008, 2019 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     Linda DeMichiel - 2.1
//     Linda DeMichiel - 2.0


package javax.persistence;

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

/**
 * Specifies the mapping for the key column of a map whose
 * map key is a basic type. If the <code>name</code> element is not specified, it
 * defaults to the concatenation of the following: the name of the
 * referencing relationship field or property; "_"; "KEY".
 * 
 * <pre>
 *    Example:
 *
 *    &#064;Entity
 *    public class Item {
 *       &#064;Id int id;
 *       ...
 *       &#064;ElementCollection
 *       &#064;MapKeyColumn(name="IMAGE_NAME")
 *       &#064;Column(name="IMAGE_FILENAME")
 *       &#064;CollectionTable(name="IMAGE_MAPPING")
 *       Map&#060;String, String&#062; images;  // map from image name to filename
 *       ...
 *    } 
 * </pre>
 * @since 2.0
 */
@Target( { METHOD, FIELD })
@Retention(RUNTIME)
public @interface MapKeyColumn {

	/**
	 * (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.
         * <p> Defaults to the concatenation of the following: the name of
         * the referencing relationship field or property; "_"; "<code>KEY</code>".
	 */
	String name() default "";

	/**
	 * (Optional) Whether the column is a unique key. This is a
	 * shortcut for the <code>UniqueConstraint</code> 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.
	 */
	boolean unique() default false;

	/** (Optional) Whether the database column is nullable. */
	boolean nullable() default false;

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

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

	/**
	 * (Optional) The SQL fragment that is used when generating the DDL for the
	 * column.
	 * <p> Defaults to the generated SQL to create a
	 * column of the inferred type.
         *
	 */
	String columnDefinition() default "";

	/** (Optional) The name of the table that contains the column. 
         *
         * <p> 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.
         */
	String table() default "";

	/**
	 * (Optional) The column length. (Applies only if a string-valued column is
	 * used.)
	 */
	int length() default 255;

	/**
	 * (Optional) The precision for a decimal (exact numeric) column. (Applies
	 * only if a decimal column is used.)  
         *
         *<p> Default: 0. (The value must be set by the developer.)
	 */
	int precision() default 0; // decimal precision

	/**
	 * (Optional) The scale for a decimal (exact numeric) column. (Applies only
	 * if a decimal column is used.)
	 */
	int scale() default 0; // decimal scale
}