Java Persistence API

Primary Keys

All entities must declare a primary key/identifier
Primary keys should be of the following types: any Java primitive type, any primitive wrapper type; java.lang.String; java.util.Date; java.sql.Date
Do not use floating-point types!

Primary Key Example

A primary key may be generated by the persistence provider

Auto-Generated Key Example

The persistence provider may use a table/sequence to generate keys

Table-Generated Key Example

  @Entity
  public class MyEntity {
    private Long id;

    @Id
    @GeneratedValue(strategy=GenerationType.TABLE, generator="idGen")
    @TableGenerator(
      name="idGen",
      table="primary_key",
      pkColumnName="entity_type",
      valueColumnName="id_value",
      pkColumnValue="MyEntity")
    public Long getId() {
      return id;
    }
  }