JPA自动递增合并

Question

I have an Entity that has the following multiple fields along with a field that is autogenerated on an insert

Now everytime I want to do an update using merge() in my DAO, it will add a new entry instead of updating the current entry. I am assuming this is due to UPDATE statement on id and the id is new everytime. Is there a way within JPA (Hibernate) to avoid writing a new record in the database and just to an update instead. Please find below my entity object:

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "CONFIG_ID")
private long configID;

@ManyToOne
@JoinColumns({
        @JoinColumn(name = "CID", referencedColumnName = "CID", insertable = true, updatable = false),
        @JoinColumn(name = "DID", referencedColumnName = "DID", insertable = true, updatable = false)})
@Version private <Object> dE;
@Column(name = "HISTORY", nullable = false, unique = false)
private String history;

Answer 1

merge() is supposed for detached entity use . It is an update or insert action depending if the identity of the merged object is null or not. If it is null , a new record will be inserted.

To correctly update an entity in JPA , you simply load it and change its properties. When the transaction commit , JPA will figure out if there are any properties changes and issue the UPDATE SQL if there are changes. No need to call any methods on EntityManager for any update.

Reference:

• JPA wiki - Merge