Monday, November 25, 2013

I am trying to use Hibernate for a multi threaded application wherein each thread retrieves an object and tries to insert it into a table. My code looks like below. I have local hibernate Session objects per thread and in each InsertData I do beginTransaction and commit.
The problem I am facing is that many times I get "org.hibernate.TransactionException: nested transactions not supported"
Since I am new to hibernate I don't know if what I am doing is correct or not? Please let me know what is the correct way to use hibernate in multi threaded app and how to avoid the above mentioned exception.
Thanks
public class Worker extends Thread {
private Session session = null;

Worker() {
    SessionFactory sf = HibernateUtil.getSessionFactory(); // Singleton
    session = sf.openSession();
    session.setFlushMode(FlushMode.ALWAYS);
}

public void run() {
    // Some loop which will run thousand of times 
    for (....)
    {
        InsertData(b);
    }
    session.close();
}

// BlogPost Table has (pk = id AutoGenerated), dateTime, blogdescription etc. 
private void InsertData(BlogPost b) {
    session.beginTransaction();
    Long id = (Long) session.save(b);
    b.setId(id);
    session.getTransaction().commit();
}
}
My hibernate config file has c3p0.min_size=10 and c3p0.max_size=20
share|improve this question
 
Is that supposed to be b.setId()? –  Lee Meador Aug 13 at 17:24
 
Yep, just corrected it. Typo happened while trying to create a minimal example of my actual code. –  RahulAug 13 at 17:27
add comment
With session-objects-per-thread, as long as you are not sharing session objects between multiple threads, you will be fine.
The error you are receiving is unrelated to your multithreaded usage or your session management. Your usage of session.save() as well as explicitly setting the ID is not quite right.
Without seeing your mapping for BlogPost its hard to tell, but if you have told Hibernate to use theid field as the primary key, and you are using the native generator for primary keys, the all you need to do is this:
session.beginTransaction();
session.persist(b);
session.flush(); // only needed if flush mode is "manual"
session.getTransaction().commit();
Hibernate will fill in the ID for you, persist() will cause the insert to happen within the bounds of the transaction (save() does not care about transactions). If your flush mode is not set to manual then you don't need to call flush() as Transaction.commit() will handle that for you.
Note that with persist(), the BlogPost's ID is not guaranteed to be set until the session is flushed, which is fine for your usage here.
To handle errors gracefully:
try {
    session.beginTransaction();
    try {
        session.persist(b);
        session.flush(); // only needed if flush mode is "manual"
        session.getTransaction().commit();
    } catch (Exception x) {
        session.getTransaction().rollback();
        // log the error
    }
} catch (Exception x) {
    // log the error
}
By the way, I suggesting making BlogPost.setId() private, or package visible. It is most likely an implementation error if another class sets the ID explicitly (again assuming native generator, and id as primary key).
share|improve this answer
1 
Thanks Jason, I din't had rollback() due to which a previous exception was leaving a transaction open for the thread and the subsequent beginTransation's used to throw "TransactionException". –  Rahul Aug 13 at 18:01
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