MapKey


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.FIELD  ;
28  import static java.lang.annotation.ElementType.METHOD  ;
29  import static java.lang.annotation.RetentionPolicy.RUNTIME  ;
30  
31  /**
32   * Is used to specify the map key for associations of type 
33   * {@link java.util.Map}.
34   * 
35   * <p> If a persistent field or property other than the primary 
36   * key is used as a map key then it is expected to have a 
37   * uniqueness constraint associated with it.
38   *
39   * <pre>
40   *
41   *    Example 1:
42   *
43   *    &#064;Entity
44   *    public class Department {
45   *        ...
46   *        &#064;OneToMany(mappedBy="department")
47   *        &#064;MapKey(name="empId")
48   *        public Map<Integer, Employee> getEmployees() {... }
49   *        ...
50   *    }
51   *
52   *    &#064;Entity
53   *    public class Employee {
54   *        ...
55   *        &#064;Id Integer getEmpid() { ... }
56   *        &#064;ManyToOne
57   *        &#064;JoinColumn(name="dept_id")
58   *        public Department getDepartment() { ... }
59   *        ...
60   *    }
61   *
62   *    Example 2:
63   *
64   *    &#064;Entity
65   *        public class Department {
66   *        ...
67   *        &#064;OneToMany(mappedBy="department")
68   *        &#064;MapKey(name="empPK")
69   *        public Map<EmployeePK, Employee> getEmployees() {... }
70   *        ...
71   *    }
72   *
73   *    &#064;Entity
74   *        public class Employee {
75   *        &#064;EmbeddedId public EmployeePK getEmpPK() { ... }
76   *        ...
77   *        &#064;ManyToOne
78   *        &#064;JoinColumn(name="dept_id")
79   *        public Department getDepartment() { ... }
80   *        ...
81   *    }
82   *
83   *    &#064;Embeddable
84   *    public class EmployeePK {
85   *        String name;
86   *        Date bday;
87   *    }
88   * </pre>
89   *
90   * @since Java Persistence 1.0
91   */
92  @Target  ({METHOD, FIELD}) 
93  @Retention  (RUNTIME)
94  
95  public @interface MapKey {
96  
97      /**
98       * The name of the persistent field or property of the 
99       * associated entity that is used as the map key. If the 
100      * name element is not specified, the primary key of the 
101      * associated entity is used as the map key. If the 
102      * primary key is a composite primary key and is mapped 
103      * as {@link IdClass}, an instance of the primary key 
104      * class is used as the key.
105      */
106     String   name() default "";
107 }
108
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