jakarta.persistence.DiscriminatorColumn Maven / Gradle / Ivy

Go to download
/*
 * Copyright (c) 2008, 2020 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 jakarta.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 jakarta.persistence.DiscriminatorType.STRING;

/**
 * Specifies the discriminator column for the 
 * SINGLE_TABLE and 
 * JOINED {@link Inheritance} mapping strategies.
 * 
 *  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
 * 
 * 
 If the DiscriminatorColumn annotation is missing, 
 * and a discriminator column is required, the name of the 
 * discriminator column defaults to "DTYPE" and the discriminator 
 * type to {@link DiscriminatorType#STRING DiscriminatorType.STRING}.
 *
 * 
 *     Example:
 *
 *     @Entity
 *     @Table(name="CUST")
 *     @Inheritance(strategy=SINGLE_TABLE)
 *     @DiscriminatorColumn(name="DISC", discriminatorType=STRING, length=20)
 *     public class Customer { ... }
 *
 *     @Entity
 *     public class ValuedCustomer extends Customer { ... }
 * 
 *
 * @see DiscriminatorValue
 *
 * @since 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.
     *  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;
}