Get SqlDataSource To Retrieve DefaultValue of Current User

(Use ExpressionBuilder, Not DataBinding in ASP.NET 2.0)

Abstract

This article shows how to use Expression Builders in ASP.NET 2.0 to retrieve the current logged in user. DataBinding will not work so Expression Builders is the ticket. A small source file is created, the references to web.config are shown and a simple example is built.

The Problem

I recently was looking at unanswered posts in the asp.net forum, specifically this one: http://forums.asp.net/thread/1402259.aspx. I thought I understood how databinding and expressions worked, but just wanted to check myself. So, I made a simple example web page just like the post shows. (see below)

 

Then, I ran it through Lutz Roeder’s .NET Reflector and got the following from the code.

 

 

It’s pretty obvious that unless there is a username of the literal string "<% User.Identity.Name %>" no records will be find. This simply means that the build provider asp.net uses is not generating any code for us with sqldatasource that will help with the DefaultValue of parameters in a SqlDataSource.

The Solution

Expression Builder to the rescue!

To solve the problem, we need to build a simple expression builder. Without going into all the details of what an expression builder is, all you need to do is put the following code in your app_code directory and call it something like ExpressionBuilderIdentity.cs.

 

 

Then, you need to add a reference to it in your web.config as follows:

Then, specify the SqlDataSource as follows:

 

 

And, Presto, it works!

Summary

Anytime you are using one of the new datasourceID controls, you need to use expressions rather than databinding if you want to reference outside variables. Creating the code is fairly straight forward and lends itself to lots of cool possibilities.

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8 Responses to “Get SqlDataSource To Retrieve DefaultValue of Current User (ExpressionBuilder with ASP.NET 2.0)”

1. Brad Says:
   September 20th, 2006 at 12:04 am

   hey Peter,
   check out this good article :
   http://weblogs.asp.net/infinitiesloop/archive/2006/08/09/The-CodeExpressionBuilder.aspx

   using the CodeExpressionBuilder, you could use :
   DefaultValue=”<%$ Code:HttpContext.Current.User.Identity.Name%>“
   or maybe better :
   DefaultValue=”<%$ Code:CurrentUserName %>“

   the nice thing about the CodeExpressionBuilder is that you can use it for anything really:
   <%$ Code: DateTime.Now.AddDays(1) %>
   <%$ Code: “Hello World, ” + CurrentUserName %>
   <%$ Code: CurrentUserName.ToUpper() %>
   <%$ Code: “Page compiled as: ” + this.GetType().AssemblyQualifiedName %>

2. Marvin Says:
   February 14th, 2007 at 12:29 am

   You’re post is very interesting and helpful. I am still a beginner in asp.net. Would you post the vb version of declaring the ExpressionBuilderIdentity class?

   Thanks

3. hanusoftware Says:
   July 2nd, 2007 at 5:03 am

   Mentioned below is a PHP function , which can be used to navigate pages generated from the select query . ie. in the form of >

   0)
   $totalpages+=1;
   echo “( Page $page of $totalpages )     “;
   if($page>1 ){
   echo “ <<Previous “;
   }
   $next=$page+1;
   if($next Next >> “;
   }

   }
   }

   // Assuming you have Opened connection to mysql database.

   $sql=” Select * from Products “;

   // Show the pager link in form of Previous||Next

   PagerNextPrevious($sql,20,’text’);

   $rs=mysql_query($sql);
   if(mysql_num_rows($rs)>0){
   while($row=mysql_fetch_array($rs)){
   echo $row[”ProductName”].”";

   }
   }

   ?>

   http://www.hanusoftware.com

4. Claudio M. E. Bastos Iorio Says:
   September 18th, 2007 at 1:59 am

   hey Peter, great post! ( I found it a year later, exactly )
   Your solution works great, Im using it now, but I’m not very sure if I understand well. Could you explain a little bit more the Expression Builder class? Thank you very much!

5. Mike Says:
   January 5th, 2008 at 5:06 pm

   I’m working with this same problem and i can’t to think there has to be an easier way. I was thinking a lot like that other kid to try and use either the cookie , control , Query String , session, … and do something like when it asked for the control parameter or somewhere. Because all i really want to do is filter a drop down box based on what their userID is.

6. eZestian Says:
   February 14th, 2008 at 12:36 am

   Hi Peter .. Indeed a great post dude.. It really helped me as am just a beginner ..Thanks a lot

7. Gerardo Melendrez Says:
   March 21st, 2008 at 2:20 pm

   More than a year later, but here it is the VB version of the code above:

   Imports Microsoft.VisualBasic
   Imports System.Web.Compilation
   Imports System.CodeDom

   Public Class ExpressionBuilderIdentity
   Inherits ExpressionBuilder

   Public Overrides Function GetCodeExpression(ByVal entry As System.Web.UI.BoundPropertyEntry, ByVal parsedData As Object, ByVal context As System.Web.Compilation.ExpressionBuilderContext) As System.CodeDom.CodeExpression
   Dim targetClass As New CodeTypeReferenceExpression(GetType(ExpressionBuilderIdentity))
   Dim targetMethod As String = “GetIdentity”
   Dim methodParameter As CodeExpression = New CodePrimitiveExpression(entry.Expression.Trim())
   Return New CodeMethodInvokeExpression(targetClass, targetMethod, methodParameter)
   End Function

   Public Shared Function GetIdentity(ByVal param As String) As Object
   Dim returnString As String = String.Empty
   If param.ToLower().Equals(”name”) Then
   returnString = HttpContext.Current.User.Identity.Name
   End If
   Return returnString
   End Function

   End Class

8. Bob Langdon Says:
   April 1st, 2008 at 8:11 am

   This is just great, thanks so much - why isn’t this simpler by default? The likelihood of wanting to limit data by such a parameter is HUGE! Anyway, you’ve provided a fantastic solution, thanks again!

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