DiscriminatorColumn


1   /*
2    * The contents of this file are subject to the terms 
3    * of the Common Development and Distribution License 
4    * (the License).  You may not use this file except in
5    * compliance with the License.
6    * 
7    * You can obtain a copy of the license at 
8    * https://glassfish.dev.java.net/public/CDDLv1.0.html or
9    * glassfish/bootstrap/legal/CDDLv1.0.txt.
10   * See the License for the specific language governing 
11   * permissions and limitations under the License.
12   * 
13   * When distributing Covered Code, include this CDDL 
14   * Header Notice in each file and include the License file 
15   * at glassfish/bootstrap/legal/CDDLv1.0.txt.  
16   * If applicable, add the following below the CDDL Header, 
17   * with the fields enclosed by brackets [] replaced by
18   * you own identifying information: 
19   * "Portions Copyrighted [year] [name of copyright owner]"
20   * 
21   * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
22   */
23  package javax.persistence;
24  
25  import java.lang.annotation.Target  ;
26  import java.lang.annotation.Retention  ;
27  import static java.lang.annotation.ElementType.TYPE  ;
28  import static java.lang.annotation.RetentionPolicy.RUNTIME  ;
29  import static javax.persistence.DiscriminatorType.STRING;
30  
31  /**
32   * Is used to define the discriminator column for the 
33   * {@link InheritanceType#SINGLE_TABLE SINGLE_TABLE} and 
34   * {@link InheritanceType#JOINED JOINED} inheritance mapping strategies.
35   * 
36   * <p> The strategy and the discriminator column are only 
37   * specified in the root of an entity class hierarchy or
38   * subhierarchy in which a different inheritance strategy is applied
39   * 
40   * <p> If the <code>DiscriminatorColumn</code> annotation is missing, 
41   * and a discriminator column is required, the name of the 
42   * discriminator column defaults to <code>"DTYPE"</code> and the discriminator 
43   * type to {@link DiscriminatorType#STRING DiscriminatorType.STRING}.
44   *
45   * <pre>
46   *     Example:
47   *     &#064;Entity
48   *     &#064;Table(name="CUST")
49   *     &#064;Inheritance(strategy=SINGLE_TABLE)
50   *     &#064;DiscriminatorColumn(name="DISC", discriminatorType=STRING,length=20)
51   *     public class Customer { ... }
52   *
53   *     &#064;Entity
54   *     public class ValuedCustomer extends Customer { ... }
55   * </pre>
56   *
57   * @since Java Persistence 1.0
58   */
59  @Target  ({TYPE}) 
60  @Retention  (RUNTIME)
61  
62  public @interface DiscriminatorColumn {
63  
64      /**
65       * (Optional) The name of column to be used for the discriminator.
66       */
67      String   name() default "DTYPE";
68  
69      /**
70       * (Optional) The type of object/column to use as a class discriminator.
71       * Defaults to {@link DiscriminatorType#STRING DiscriminatorType.STRING}.
72       */
73      DiscriminatorType discriminatorType() default STRING;
74  
75      /**
76       * (Optional) The SQL fragment that is used when generating the DDL 
77       * for the discriminator column.
78       * <p> Defaults to the provider-generated SQL to create a column 
79       * of the specified discriminator type.
80       */
81      String   columnDefinition() default "";
82  
83      /** 
84       * (Optional) The column length for String-based discriminator types. 
85       * Ignored for other discriminator types.
86       */
87      int length() default 31;
88  }
89
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