After playing around with LINQ-to-SQL today I noticed that the generated DataContext subclass exposes a Log property of type TextWriter.

I initially replaced this with a StringWriter backed by a local StringBuilder variable so I could read the output, but then decided to take advantage of the fact that the generated class is a partial class:

//Generated class: WidgetDb.designer.cs
public partial class WidgetDbDataContext : System.Data.Linq.DataContext {
  ...
}

//My partial implementation: WidgetDbDataContext.cs
public partial class WidgetDbDataContext {
  private StringBuilder logBuilder = new StringBuilder();
  
  public String GetLoggedInformation() {
    return logBuilder.ToString();
  }

  partial void OnCreated() {
    Log = new StringWriter(logBuilder);
  }
}

I could then perform a sample query or two in my ASPX:

private void doLinqStuff() {
  WidgetDbDataContext db = new WidgetDbDataContext();      
  var widgets = from w in db.Widgets select w;
  WidgetGrid.DataSource = widgets;
  WidgetGrid.DataBind();      
  WidgetCount.Text = widgets.Count().ToString();      
  StatusLog.Text += db.GetLoggedInformation().Replace("\n", "<br/>");
}

The output of StatusLog.Text from this was:

SELECT [t0].[WidgetId], [t0].[WidgetName], [t0].[WidgetDescription], [t0].[WidgetPrice], [t0].[IsActive]
FROM [dbo].[Widgets] AS [t0]
-- Context: SqlProvider(Sql2005) Model: AttributedMetaModel Build: 3.5.20706.1

SELECT COUNT(*) AS [value]
FROM [dbo].[Widgets] AS [t0]
-- Context: SqlProvider(Sql2005) Model: AttributedMetaModel Build: 3.5.20706.1 

This is potentially helpful for learning how your expressions translate to SQL, but you probably wouldn’t want to do this in production :)

I then decided to search Google for “DataContext.Log” and found out that people far smarter than me have already come up with better solutions. Ah well, at least I learnt about extending the generated DataContext, as well as some smart ways of logging from others. :)