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/*
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 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License. You can obtain
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 * or glassfish/bootstrap/legal/LICENSE.txt.  See the License for the specific
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package javax.persistence;

import java.lang.annotation.Target;
import java.lang.annotation.Retention;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * Is used to specify the map key for associations of type 
 * {@link java.util.Map}.
 * 
 * 

If a persistent field or property other than the primary * key is used as a map key then it is expected to have a * uniqueness constraint associated with it. * *

 *
 *    Example 1:
 *
 *    @Entity
 *    public class Department {
 *        ...
 *        @OneToMany(mappedBy="department")
 *        @MapKey(name="empId")
 *        public Map getEmployees() {... }
 *        ...
 *    }
 *
 *    @Entity
 *    public class Employee {
 *        ...
 *        @Id Integer getEmpid() { ... }
 *        @ManyToOne
 *        @JoinColumn(name="dept_id")
 *        public Department getDepartment() { ... }
 *        ...
 *    }
 *
 *    Example 2:
 *
 *    @Entity
 *        public class Department {
 *        ...
 *        @OneToMany(mappedBy="department")
 *        @MapKey(name="empPK")
 *        public Map getEmployees() {... }
 *        ...
 *    }
 *
 *    @Entity
 *        public class Employee {
 *        @EmbeddedId public EmployeePK getEmpPK() { ... }
 *        ...
 *        @ManyToOne
 *        @JoinColumn(name="dept_id")
 *        public Department getDepartment() { ... }
 *        ...
 *    }
 *
 *    @Embeddable
 *    public class EmployeePK {
 *        String name;
 *        Date bday;
 *    }
 * 
* * @since Java Persistence 1.0 */ @Target({METHOD, FIELD}) @Retention(RUNTIME) public @interface MapKey { /** * The name of the persistent field or property of the * associated entity that is used as the map key. If the * name element is not specified, the primary key of the * associated entity is used as the map key. If the * primary key is a composite primary key and is mapped * as {@link IdClass}, an instance of the primary key * class is used as the key. */ String name() default ""; }




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