why Oracle sequence not working with JPA entity ID?

Suppose you have an Oracle sequence defined as following:

 

 

CREATE SEQUENCE BILLING.SEQ_ACTVID
	START WITH 300060
	INCREMENT BY 1
	NOMINVALUE
	NOMAXVALUE
	NOCYCLE
	NOORDER
	CACHE 20;

 

 

And you want to use that Oracle sequence. You need to add attribute "allocationSize=1" in "@SequenceGenerator" when decroating the Entity bean.

 

  @Id
  @Column(name="ACTVID", nullable = false)
  @SequenceGenerator(name="SeqACTVID", sequenceName="SEQ_ACTVID", allocationSize=1)
  @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="SeqACTVID")
  private Long ACTVID;

 

Otherwise, ORM implementation underneath JPA might randomly allocate sequence number for you. This might cause problems that you don't expect, such as unique constraint violation errors from Oracle. You might also notice that the Oralce sequence generator seems to ignore your "start with" defination as well, if you missed out the "allocationSize=1" attribute.