How to configure Fluent NHibernate to output queries to Trace or Debug instead of Console?

You probably want to use log4net, not ShowSql. Here is some configuration to send queries to Debug:

  <configSections>
    <section name="log4net"
     type="log4net.Config.Log4NetConfigurationSectionHandler,log4net" />
  </configSections>

  <log4net debug="false">
    <appender name="WindowsDebugOutput" type="log4net.Appender.DebugAppender,
         log4net">
      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern"
              value="%d{ABSOLUTE} %-5p %c{1}:%L - %m%n" />
      </layout>
    </appender>

    <logger name="NHibernate.SQL" additivity="false">
      <level value="DEBUG" />
      <appender-ref ref="WindowsDebugOutput" />
    </logger>
  </log4net>

And then call this from your code before opening an NHibernate session:

log4net.Config.XmlConfigurator.Configure();

When you add a reference to the log4net DLL, make sure to set its "Copy Local" property to "true".

This isn't specific to FluentNHibernate, it works the same in any variant of NHibernate.

I have not tried this with SQL Server, but with SQLite, the following code will show generated SQL in the Output window (Debug menu -> Windows -> Output, in VS2008).

The "Show output from:" combo box in the Output window should be set to "Debug" - VS2008 did that for me automatically.

            sessionFactory = Fluently.Configure()
                .Database(SQLiteConfiguration.Standard
                            .UsingFile(DbFile)
                            // Display generated SQL in Output window
                            .ShowSql()
                          )
                .Mappings(m => m.AutoMappings.Add( GetAutoPersistenceModel() ))
                .BuildSessionFactory()
                ;

A word of warning - turning this on can slow down execution considerably.