EclipseLink/UserGuide/JPA/Basic JPA Development/Entities/Ids/Id

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Use the @Id annotation to designate one or more persistent fields or properties as the entity's primary key.

For each entity, you must designate at least one of the following:

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Note: The last option in the preceding list – @Id and @IdClass combination – is applicable to composite primary key configuration.

The @Id annotation does not have attributes.

By default, the entities Id must be set by the application, normally before the persist is called. A @GeneratedValue can be used to have EclipseLink generate the Id value.

This example shows how to use this annotation to designate the persistent field empID as the primary key of the Employee table.

Usage of @Id Annotation

 public class Employee implements Serializable {
     private int empID;

The @Id annotation supports the use of EclipseLink converters (see Using EclipseLink JPA Converters).

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For more information, see Section 9.1.8 "Id Annotation" in the JPA Specification.

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