Revision as of 11:43, 28 June 2012

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Key API

• @GeneratedValue
• @UuidGenerator

@UuidGenerator

You can use the @UuidGenerator to generate an object's Id based on a Universally Unique IDentifier (UUID). A UUID is a globally unique id. A UUID does not require database access, so is efficient to generate, but is a large value, so requires more storage than a numeric id. A UUID can be stored as a String (32 bytes) or a byte[] (16 bytes). UUIDs are useful in distributed architectures as they do not require a single generation point.

The following example shows how to use this annotation to specify the allocation size for the SEQUENCE primary key generator named Emp_Seq.

Example: @UuidGenerator

 @Entity
 public class Employee implements Serializable {
     ...
     @Id
     @UuidGenerator(name="UUID")
     @GeneratorValue(generator="UUID")
     @Column(name="EMP_ID")
     public String getId() {
         return id;
     }
     ...
 }

Example: Using <sequence-generator>

<entity class="Employee">
    <attributes>
        <id name="id">
            <column name="EMP_ID"/>
            <generated-value generator="UUID"/>
            <uuid-generator name="UUID"/>
        </id>
        ...
    </attributes>
</entity>

@SequenceGenerator	Configuring Entities	@Table
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