001/*
002 * Copyright (c) 2008, 2009, 2011 Oracle, Inc. All rights reserved.
003 *
004 * This program and the accompanying materials are made available under the
005 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
006 * which accompanies this distribution.  The Eclipse Public License is available
007 * at http://www.eclipse.org/legal/epl-v10.html and the Eclipse Distribution License
008 * is available at http://www.eclipse.org/org/documents/edl-v10.php.
009 */
010package javax.persistence;
011
012import java.lang.annotation.Retention;
013import java.lang.annotation.Target;
014
015import static java.lang.annotation.ElementType.TYPE;
016import static java.lang.annotation.RetentionPolicy.RUNTIME;
017import static javax.persistence.DiscriminatorType.STRING;
018
019/**
020 * Specifies the discriminator column for the <code>SINGLE_TABLE</code> and <code>JOINED</code>
021 * {@link Inheritance} mapping strategies.
022 * <p>
023 * The strategy and the discriminator column are only specified in the root of an entity class hierarchy or
024 * subhierarchy in which a different inheritance strategy is applied
025 * <p>
026 * If the <code>DiscriminatorColumn</code> annotation is missing, and a discriminator column is required, the
027 * name of the discriminator column defaults to <code>"DTYPE"</code> and the discriminator type to
028 * {@link DiscriminatorType#STRING DiscriminatorType.STRING}.
029 * <p>
030 * <pre>
031 *     Example:
032 *
033 *     &#064;Entity
034 *     &#064;Table(name="CUST")
035 *     &#064;Inheritance(strategy=SINGLE_TABLE)
036 *     &#064;DiscriminatorColumn(name="DISC", discriminatorType=STRING, length=20)
037 *     public class Customer { ... }
038 *
039 *     &#064;Entity
040 *     public class ValuedCustomer extends Customer { ... }
041 * </pre>
042 *
043 * @see DiscriminatorValue
044 * @since Java Persistence 1.0
045 */
046@Target({TYPE})
047@Retention(RUNTIME)
048public @interface DiscriminatorColumn {
049
050  /**
051   * (Optional) The name of column to be used for the discriminator.
052   *
053   * @return col name
054   */
055  String name() default "DTYPE";
056
057  /**
058   * (Optional) The type of object/column to use as a class discriminator. Defaults to
059   * {@link DiscriminatorType#STRING DiscriminatorType.STRING}.
060   *
061   * @return discrim type
062   */
063  DiscriminatorType discriminatorType() default STRING;
064
065  /**
066   * (Optional) The SQL fragment that is used when generating the DDL for the discriminator column.
067   * <p>
068   * Defaults to the provider-generated SQL to create a column of the specified discriminator type.
069   *
070   * @return col def
071   */
072  String columnDefinition() default "";
073
074  /**
075   * (Optional) The column length for String-based discriminator types. Ignored for other discriminator
076   * types.
077   *
078   * @return length
079   */
080  int length() default 31;
081}