Hi all,

i am new to Hibernate and i need your help in peculiar situation i am facing.

I am having a mapping file which has lazy="false" at class declaration level and employs native sequence generator from database i.e, sequence is present in the database which provides next id.

Our application whenever is creating an instance of this particular class say X, also increments the version_id before saving it to database.

Here is the sequence:
X x = new X();
saveEntity(x);

saveEntity(x) -- is just normal saveOrUpdate() wrapper.

The table contains entries not in ascending order.

rownum ---- x_id
-----------------
1 -- 101
2 --- 102
3-- 105
4 -- 103
5--104
------------------------

I am wondering what is causing this behavior. Is it possible that when i do X x = new X(), the hibernate fetches the x_id from the native sequence generator and attaches to it before the actual commit to the database. Meanwhile if the another user is creating another instance he will get next instance of x and also the next x_id.

SO, whoever commits to da database first wins, regardless who got the least x_id.

Although i think i am wrong, i need your help/comments.

thanks in advance,

You are right. The first commit makes it to database. If you want to double check this roll back the transaction and see if you lose ids.



Farzad-

Can you please elaborate on this behavior.. i mean why is it happening..is it because we had set lazy="false" at class level or is it that we are using native sequence generator.

why should hibernate pick the next sequence for the class id before the user saves the object to the database.

Is it not wrong say, like the user creates new x() but later decides not to commit that object to the database. In this scenario sequence id 103 is picked up but not used, while other users continue to next sequences and commit to the database.

please correct me, if i am wrong..

The id is not picked when an instance is creates since hibernate has no clue you are creating an entity. It is allocated when the call to save is made but calling save does not necessarily flush to database right away.


Farzad-

thanks once again for the clarification.

Did you mean to say hibernate got the next sequence when i saved the object but the object is not flushed(committed) to the database immediately.
Meanwhile other users changes have been flushed to the database and thats the reason the entries in the database are in different order..

Can you pls also tell me is there a way i can make sure the changes made while saving the object are flushed to the database immediately..

There are different ways to manage the flush mode. One is via hibernate property 'org.hibernate.flushmode' in your hibernate config file and you can set it to always or commit or manual. Or you can override the default behaviour at a specific method level by creating a query or criteria by setting the FlushMode parameter. But its generally better to leave the flush mode alone ("auto" mode).
In your case, I believe you may have X as a parent or a child of another element. And when X is persisted, it issues a create (with version 0) and issues an update (incrementing version to 1) to add the association to its parent or child. Hence, 2 sqls issued for the same instance and the reason behind version number being incremented.
Regarding the ordering of the records.. I think its just the db client you're using which by default is not ordering the ids.. Do you have a timestamp on the records as to when they were created? Im pretty sure record 105 would not have been created before record 104.

Regards,
Arun

You could call the flush right after save.



Farzad-