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package javax.persistence;

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

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

/**
 * Applied to a persistent field or property of an entity class or mapped superclass to denote a composite primary key that is an embeddable
 * class. The embeddable class must be annotated as {@link Embeddable}.
 * 
 * 
 * There must be only one EmbeddedId annotation and no Id annotation when the EmbeddedId annotation
 * is used.
 * 
 * 

 * The {@link AttributeOverride} annotation may be used to override the column mappings declared within the embeddable class.
 * 
 * 

 * The {@link MapsId} annotation may be used in conjunction with the EmbeddedId annotation to specify a derived primary key.
 * 
 * 

 * If the entity has a derived primary key, the AttributeOverride annotation may only be used to override those attributes of
 * the embedded id that do not correspond to the relationship to the parent entity.
 * 
 * 

 * Relationship mappings defined within an embedded id class are not supported.
 * 
 * 
 *    Example 1:
 * 
 *    @EmbeddedId
 *    protected EmployeePK empPK;
 * 
 * 
 *    Example 2:
 * 
 *    @Embeddable
 *    public class DependentId {
 *       String name;
 *       EmployeeId empPK;   // corresponds to primary key type of Employee
 *    }
 * 
 *    @Entity
 *    public class Dependent {
 *       // default column name for "name" attribute is overridden
 *       @AttributeOverride(name="name", @Column(name="dep_name"))
 *       @EmbeddedId DependentId id;
 *       ...
 *       @MapsId("empPK")
 *       @ManyToOne Employee emp;
 *    }
 * 
 * 
 * @see Embeddable
 * @see MapsId
 * 
 * @since Java Persistence 1.0
 */
@Target({ METHOD, FIELD })
@Retention(RUNTIME)
public @interface EmbeddedId {}