detached entity passed to persist error with JPA EJB code

Question

I am trying to run this basic JPA EJB code   public static void main String   args            UserBean user   new UserBean             user setId 1            user setUserName  name1             user setPassword  passwd1             em persist user         I get this error   javax ejb EJBException  javax persistence PersistenceException  org hibernate PersistentObjectException  detached entity passed to persist  com JPA Database   Any ideas   I search on the internet and the reason I found was       This was caused by how you created the objects  i e  If you set the ID property explicitly  Removing ID assignment fixed it    But I didn t get it  what will I have to modify to get the code working

User · Answer

remove   user setId 1     because it is auto generate on the DB  and continue with persist command

User · Answer

I had this problem and it was caused by the second level cache    I persisted an entity using hibernate Then I deleted the row created from a separate process that didn t interact with the second level cache I persisted another entity with the same identifier  my identifier values are not auto-generated    Hence  because the cache wasn t invalidated  hibernate assumed that it was dealing with a detached instance of the same entity

User · Answer

I got the answer  I was using   em persist user     I used merge in place of persist   em merge user     But no idea  why persist didn t work

User · Answer

The error occurs because the object s ID is set  Hibernate distinguishes between transient and detached objects and persist works only with transient objects  If persist concludes the object is detached  which it will because the ID is set   it will return the  detached object passed to persist  error  You can find more details here and here   However  this only applies if you have specified the primary key to be auto-generated  if the field is configured to always be set manually  then your code works

User · Answer

If you set id in your database to be primary key and autoincrement  then this line of code is wrong     user setId 1     Try with this   public static void main String   args            UserBean user   new UserBean             user setUserName  name1             user setPassword  passwd1             em persist user

User · Answer

Here  persist   only will insert the record If we use  merge   it will check is there any record exist with the current ID  If it exists  it will update otherwise it will insert a new record

User · Answer

if you use to generate the id   GenerationType AUTO strategy in your entity   Replaces user setId  1  by user setId  null   and the problem is solved

User · Answer

Let s say you have two entities Album and Photo  Album contains many photos  so it s a one to many relationship   Album class   Entity public class Album        Id      GeneratedValue strategy GenerationType AUTO      Integer albumId       String albumName        OneToMany targetEntity Photo class mappedBy  album  cascade  CascadeType ALL  orphanRemoval true      Set lt Photo gt  photos   new HashSet lt Photo gt         Photo class   Entity public class Photo       Id      GeneratedValue strategy GenerationType AUTO      Integer photo id       String photoName        ManyToOne targetEntity Album class       JoinColumn name  album id       Album album       What you have to do before persist or merge is to set the Album reference in each photos           Album myAlbum   new Album            Photo photo1   new Photo            Photo photo2   new Photo             photo1 setAlbum myAlbum           photo2 setAlbum myAlbum            That is how to attach the related entity before you persist or merge

User · Answer

I know its kind of too late and proly every one got the answer  But little bit more to add to this  when GenerateType is set  persist   on an object is expected to get an id generated   If there is a value set to the Id by user already  hibernate treats it as saved record and so it is treated as detached   if the id is null - in this situation a null pointer exception is raised when the type is AUTO or IDENTITY etc unless the id is generated from a table or a sequece etc   design  this happens when the table has a bean property as primary key  GenerateType must be set only when an id is autogenerated  remove this and the insert should work with the user specified id   it is a bad design to have a property mapped to primary key field

[java] "detached entity passed to persist error" with JPA/EJB code

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