Question

How to configure Fluent NHibernate to output queries to Trace or Debug instead of Console?
I’m using MsSqlConfiguration.MsSql2008.ShowSql() but it has no parameters and I can’t find anything on Google.

Answer 1

I can see from forum and blog posts everywhere that lots of others before me have looked for a way to get the SQL statements as they’re being prepared for execution. The answer typically is something along the lines of "you can’t", or "you shouldn’t".

Whether I should or not, that’s what I wanted.

After hours of searching, investigation and failed attempts, and finally I came up with this.

Write up an interceptor:

using NHibernate;
using System.Diagnostics;

public class SqlStatementInterceptor : EmptyInterceptor
{
    public override NHibernate.SqlCommand.SqlString OnPrepareStatement(NHibernate.SqlCommand.SqlString sql)
    {
        Trace.WriteLine(sql.ToString());
        return sql;
    }
}

Of course, you don’t have to Trace.WriteLine() here, you could write it to a log file, or whatever else you need.

In your connection manager, hook up your Interceptor like so:

protected virtual void Configure(FluentConfiguration config)
{
    config.ExposeConfiguration(x =>
                                   {
                                       x.SetInterceptor(new SqlStatementInterceptor());
                                   });
}

It’s not that complicated. From my perspective, certainly easier than trying to get all this XML pushed through Fluent to NHibernate – since Fluent abstracts the XML file away.

Keep in mind, you can only have a single Interceptor – so you may need to integrate this feature with your existing Interceptor, if you already have one. On that note, you might want to give it a broader name – e.g. MyAppInterceptor, so as not to imply a specific purpose, because you may want to add other features to it later.