NHibernate should always write NULL instead of empty string

Question

I use NHibernate 3 with Microsoft SQL Server Database (2005 and higher). Now, I am searching a way to tell NHibernate to write always NULL to the database instead of empty strings. What would be the best way to do this? - Or is there perhaps a switch in NHibernate to do this? Thanks for your help.

Answer 1

You can add a PreInsertEventListener and override the function to do the necessary conversion of an empty string to a NULL value.

The way to go about this would be:

 public class NhibernateEventListeners :  IPreInsertEventListener
    {
         public bool OnPreInsert(PreInsertEvent nHibernateEvent)
        {
            var entityBeingInserted = nHibernateEvent.Entity;
            if (entityBeingInserted == null)
                return false;
             if (property.PropertyType==typeof(string))
                 {
                    //use reflection to set the property value to null   
                 }
            return false;
        }
   }

and while setting up the sessionfactory make sure you add the following to your configuration

_config.ExposeConfiguration(
                        config => config.SetListener(ListenerType.PreInsert, new NhibernateEventListeners()));

Hope this is what you are looking for and helps you.