How to Track Queries on a Linq-to-sql DataContext

Question

In the herding code podcast 14 someone mentions that stackoverflow displayed the queries that were executed during a request at the bottom of the page.

It sounds like an excellent idea to me. Every time a page loads I want to know what sql statements are executed and also a count of the total number of DB round trips. Does anyone have a neat solution to this problem?

What do you think is an acceptable number of queries? I was thinking that during development I might have my application throw an exception if more than 30 queries are required to render a page.

EDIT: I think I must not have explained my question clearly. During a HTTP request a web application might execute a dozen or more sql statements. I want to have those statements appended to the bottom of the page, along with a count of the number of statements.

HERE IS MY SOLUTION:

I created a TextWriter class that the DataContext can write to:

public class Logger : StreamWriter { public string Buffer { get; private set; } public int QueryCounter { get; private set; }

    public Logger() : base(new MemoryStream())
    {}

    public override void Write(string value)
    {
        Buffer += value + "<br/><br/>";
        if (!value.StartsWith("--")) QueryCounter++;
    }

    public override void WriteLine(string value)
    {
        Buffer += value + "<br/><br/>";
        if (!value.StartsWith("--")) QueryCounter++;
    }
}

In the DataContext's constructor I setup the logger:

public HeraldDBDataContext()
        : base(ConfigurationManager.ConnectionStrings["Herald"].ConnectionString, mappingSource)
    {
        Log = new Logger();
    }

Finally, I use the Application_OnEndRequest event to add the results to the bottom of the page:

protected void Application_OnEndRequest(Object sender, EventArgs e)
    {
        Logger logger = DataContextFactory.Context.Log as Logger;
        Response.Write("Query count : " + logger.QueryCounter);
        Response.Write("<br/><br/>");
        Response.Write(logger.Buffer);
    }

Answer 1

If you put .ToString() to a var query variable you get the sql. You can laso use this in Debug en VS2008. Debug Visualizer

ex:

var query = from p in db.Table
            select p;

MessageBox.SHow(query.ToString());

Answer 2

From Linq in Action

Microsoft has a Query Visualizer tool that can be downloaded separetly from VS 2008. it is at http://weblogs.asp.net/scottgu/archive/2007/07/31/linq-to-sql-debug-visualizer.aspx

Answer 3

System.IO.StreamWriter httpResponseStreamWriter = 
new StreamWriter(HttpContext.Current.Response.OutputStream);

dataContext.Log = httpResponseStreamWriter;

Stick that in your page and you'll get the SQL dumped out on the page. Obviously, I'd wrap that in a little method that you can enable/disable.

Answer 4

I have a post on my blog that covers sending to log files, memory, the debug window or multiple writers.