src/javax/persistence/DiscriminatorColumn.java

/*******************************************************************************
 * Copyright (c) 1998, 2009 Oracle. All rights reserved. 
 * 
 * This program and the accompanying materials are made available under the 
 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0 
 * which accompanies this distribution. 
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at 
 * http://www.eclipse.org/org/documents/edl-v10.php.
 * 
 * The API for this class and its comments are derived from the JPA 2.0 specification 
 * which is developed under the Java Community Process (JSR 317) and is copyright 
 * Sun Microsystems, Inc. 
 *
 * Contributors:
 *     dclarke - Java Persistence 2.0 - Proposed Final Draft (March 13, 2009)
 *               Specification and licensing terms available from
 *               http://jcp.org/en/jsr/detail?id=317
 *
 * EARLY ACCESS - PUBLIC DRAFT
 * This is an implementation of an early-draft specification developed under the 
 * Java Community Process (JCP) and is made available for testing and evaluation 
 * purposes only. The code is not compatible with any specification of the JCP.
 ******************************************************************************/

package javax.persistence;

import java.lang.annotation.Target;
import java.lang.annotation.Retention;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import static javax.persistence.DiscriminatorType.STRING;

/**
 * Is used to define the discriminator column for the 
 * {@link InheritanceType#SINGLE_TABLE SINGLE_TABLE} and 
 * {@link InheritanceType#JOINED JOINED} inheritance mapping strategies.
 * 
 * <p> The strategy and the discriminator column are only 
 * specified in the root of an entity class hierarchy or
 * subhierarchy in which a different inheritance strategy is applied
 * 
 * <p> If the <code>DiscriminatorColumn</code> annotation is missing, 
 * and a discriminator column is required, the name of the 
 * discriminator column defaults to <code>"DTYPE"</code> and the discriminator 
 * type to {@link DiscriminatorType#STRING DiscriminatorType.STRING}.
 *
 * <pre>
 *     Example:
 *     &#064;Entity
 *     &#064;Table(name="CUST")
 *     &#064;Inheritance(strategy=SINGLE_TABLE)
 *     &#064;DiscriminatorColumn(name="DISC", discriminatorType=STRING,length=20)
 *     public class Customer { ... }
 *
 *     &#064;Entity
 *     public class ValuedCustomer extends Customer { ... }
 * </pre>
 *
 * @since Java Persistence API 1.0
 */
@Target({TYPE}) 
@Retention(RUNTIME)

public @interface DiscriminatorColumn {

    /**
     * (Optional) The name of column to be used for the discriminator.
     */
    String name() default "DTYPE";

    /**
     * (Optional) The type of object/column to use as a class discriminator.
     * Defaults to {@link DiscriminatorType#STRING DiscriminatorType.STRING}.
     */
    DiscriminatorType discriminatorType() default STRING;

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

    /** 
     * (Optional) The column length for String-based discriminator types. 
     * Ignored for other discriminator types.
     */
    int length() default 31;
}