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.

check http://stackoverflow.com/questions/2592556/how-to-have-nhibernate-persist-a-string-empty-property-value-as-null and also http://stackoverflow.com/questions/1187841/mapping-empty-strings-to-null-in-nhibernate — V4Vendetta, Mar 22 '12 at 08:37
Hi. Thanks for your links. I have a question: I have seen, that they work with Fluent. I work with hbm-mappings. Will this also work with hbm-mappings? — BennoDual, Mar 22 '12 at 09:22
You can use custom IUserType with hbm-mappings too. Example `` — Nikolay, Mar 22 '12 at 09:56

score 0 · Accepted Answer · answered Mar 22 '12 at 14:13

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.

NHibernate should always write NULL instead of empty string

1 Answers1