Why does a IQuery.List result in a dirty session?

daver · **Joined:** Thu Sep 17, 2009 11:22 am **Posts:** 10

Can someone tell me why the following code results in a dirty session?

Code:

    
    using (ITransaction t = CurrentSession.BeginTransaction())
    {
        IQuery query = CurrentSession.CreateQuery("from SensorHistory srh "
                                + "where srh.Sensor = :sensor "
                                + "and srh.ReadingTimeUTC between :startDate and :endDate");
        query.SetParameter("sensor", sensor);
        query.SetParameter("startDate", startDateUTC);
        query.SetParameter("endDate", endDateUTC);

        var list = query.List<SensorHistory>();

        t.Commit();
   }

If I check the "CurrentSession.IsDirty()" before query.List<SensorHistory>() it returns false but true after. The problem is these entities come from a large table so when the enclosing transaction is committed, it tries to write these entities back to the DB, which causes a table scan that takes a very LOONNGGG time.

Thanks,
Dave

daver · **Joined:** Thu Sep 17, 2009 11:22 am **Posts:** 10

This seems to be a more general problem. Whenever we query entities from the DB, NHibernate updates all values for the entity when the transaction is committed, even though none of the attributes are changed...at least by my code.

kir · **Posted:** Thu Apr 15, 2010 2:04 am

http://nhforge.org/doc/nh/en/index.html#manipulatingdata-flushing
Use FlushMode.

daver · **Joined:** Thu Sep 17, 2009 11:22 am **Posts:** 10

Thanks, but FlushMode won't help me. I'm not modifying any of the entities I'm fetching. I simply do a query with no update. When I commit, any entity I've fetched is written back weather I've updated it or not.

daver · **Joined:** Thu Sep 17, 2009 11:22 am **Posts:** 10

kir · **Posted:** Fri Apr 16, 2010 4:46 am

Test like this:

Code:

using (ITransaction t = CurrentSession.BeginTransaction())
    {
        CurrentSession.FlushMode = FlushMode.Never;

        IQuery query = CurrentSession.CreateQuery("from SensorHistory srh "
                                + "where srh.Sensor = :sensor "
                                + "and srh.ReadingTimeUTC between :startDate and :endDate");
        query.SetParameter("sensor", sensor);
        query.SetParameter("startDate", startDateUTC);
        query.SetParameter("endDate", endDateUTC);

        var list = query.List<SensorHistory>();

        t.Commit();
   }

or without Transaction:

Code:

    IQuery query = CurrentSession.CreateQuery("from SensorHistory srh "
                                + "where srh.Sensor = :sensor "
                                + "and srh.ReadingTimeUTC between :startDate and :endDate");
        query.SetParameter("sensor", sensor);
        query.SetParameter("startDate", startDateUTC);
        query.SetParameter("endDate", endDateUTC);

        var list = query.List<SensorHistory>();

daver · **Joined:** Thu Sep 17, 2009 11:22 am **Posts:** 10

I think you've missed the point of my question. I want to know why this is happening. ASAIK, this should not happen if I only read an entity and do not modify it.

I realize I can manipulate the FlushMode but that's not the point.

wolli · **Posted:** Sat Apr 17, 2010 3:03 am

Have a look at this: http://nhforge.org/doc/nh/en/index.html#events. I think it's the FindDirty method you need. Implement an interceptor (there's n EmptyInterceptor for start) and set a breakpoint in that method. You should be able to figure out why hibernate considers your object dirty there. In my experience there is something in your setters, that makes changes to the object.