/*
 * Copyright (c) 2008, 2009, 2011 Oracle, Inc. 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.
 */
package javax.persistence;

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

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

Specifies the discriminator column for the SINGLE_TABLE and JOINED 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 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 Also:
DiscriminatorValue
Since:
Java Persistence 1.0/**
 * Specifies the discriminator column for the <code>SINGLE_TABLE</code> and <code>JOINED</code>
 * {@link 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}.
 * <p>
 * <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>
 *
 * @see DiscriminatorValue
 * @since Java Persistence 1.0
 */
@Target({TYPE})
@Retention(RUNTIME)
public @interface DiscriminatorColumn {

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

  
(Optional) The type of object/column to use as a class discriminator. Defaults to DiscriminatorType.STRING. 
Returns:
discrim type/**
   * (Optional) The type of object/column to use as a class discriminator. Defaults to
   * {@link DiscriminatorType#STRING DiscriminatorType.STRING}.
   *
   * @return discrim type
   */
  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.
Returns:
col def/**
   * (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.
   *
   * @return col def
   */
  String columnDefinition() default "";

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