Copyright (c) 2008 - 2013 Oracle Corporation. 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.
Contributors:
    Linda DeMichiel - Java Persistence 2.1
    Linda DeMichiel - Java Persistence 2.0
/*******************************************************************************
 * Copyright (c) 2008 - 2013 Oracle Corporation. 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.
 *
 * Contributors:
 *     Linda DeMichiel - Java Persistence 2.1
 *     Linda DeMichiel - Java Persistence 2.0
 *
 ******************************************************************************/ 
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;

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