JPA - Returning an auto generated id after persist

Question

I m using JPA  EclipseLink  and Spring  Say I have a simple entity with an auto-generated ID    Entity public class ABC implements Serializable         Id       GeneratedValue strategy GenerationType IDENTITY       private int id                   In my DAO class  I have an insert method that calls persist   on this entity  I want the method to return the generated ID for the new entity  but when I test it  it returns 0 instead   public class ABCDao        PersistenceContext     EntityManager em        Transactional readOnly false      public int insertABC ABC abc             em persist abc               I WANT TO RETURN THE AUTO-GENERATED ID OF abc             HOW CAN I DO IT           return abc id                   I also have a service class that wraps the DAO  if that makes a difference   public class ABCService        Resource name  ABCDao       ABCDao abcDao       public int addNewABC ABC abc             return abcDao insertABC abc

User · Answer

This is how I did it   EntityManager entityManager   getEntityManager    EntityTransaction transaction   entityManager getTransaction    transaction begin    entityManager persist object   transaction commit    long id   object getId    entityManager close

User · Answer

em persist abc   em refresh abc   return abc

User · Answer

The ID is only guaranteed to be generated at flush time  Persisting an entity only makes it  attached  to the persistence context  So  either flush the entity manager explicitely   em persist abc   em flush    return abc getId      or return the entity itself rather than its ID  When the transaction ends  the flush will happen  and users of the entity outside of the transaction will thus see the generated ID in the entity    Override public ABC addNewABC ABC abc        abcDao insertABC abc       return abc

User · Answer

You could also use GenerationType TABLE instead of IDENTITY which is only available after the insert

User · Answer

Entity public class ABC implements Serializable         Id       GeneratedValue strategy GenerationType IDENTITY       private int id         check that  GeneratedValue notation is there in your entity class This tells JPA about your entity property auto-generated behavior

User · Answer

Another option compatible to 4 0   Before committing the changes  you can recover the new CayenneDataObject object s  from the collection associated to the context  like this   CayenneDataObject dataObjectsCollection    CayenneDataObject cayenneContext newObjects      then access the ObjectId for each one in the collection  like   ObjectId objectId   dataObject getObjectId      Finally you can iterate under the values  where usually the generated-id is going to be the first one of the values  for a single column key  in the Map returned by getIdSnapshot    it contains also the column name s  associated to the PK as key s    objectId getIdSnapshot   values

User · Answer

This is how I did it  You can try      public class ABCService        Resource name  ABCDao       ABCDao abcDao       public int addNewABC ABC abc             ABC setId 0            return abcDao insertABC abc

[java] JPA - Returning an auto generated id after persist()

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