Nested GridView controls in ASP.NET: best practices

General solution

Nesting GridView controls in ASP.NET were described in that almost “canonical” Microsoft walkthrough [1]. In general, it requires creating of two GridView controls: the first one serving as a container or master GridView1 with its own DataSource1 (SqlDataSource, AccessDataSource, etc.) and second "nested" GridView2 with its underlying DataSource2 residing within a TemplateField in master GridView1.

Code snippet [1] inside the GridView1 RowDataBound event procedure (GridView1_RowDataBound) serves the task of passing a "foreign key" value from GridView1 to DataSource2. In the particular example provided in [1], the “foreign key” stored in first cell of GridView1 (e.Row.Cells[0].Text) is passed to DefaultValue property of only one SelectParameter (SelectParameters[0]) of SqlDataSource2:

Listing 1. Original solution on MSDN w/hardcoded Cells index

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e){
  if (e.Row.RowType == DataControlRowType.DataRow)
  {
    SqlDataSource s = (SqlDataSource)e.Row.FindControl("SqlDataSource2");
    s.SelectParameters[0].DefaultValue = e.Row.Cells[0].Text;
  }
}

This should work in all practical versions of ASP.NET (2.0/3.5/4.0). However, the potential drawback of this solution rises from the fact that the foreign key value (for example, ID) could be omitted from visible fields set of GridView1 control. Also, even in case this foreign key field is presented in GridView1, then there is potential inconvenience of hard-coded Cell index of 0; generally, it can be not the first one in the field set and, also, its index could change dynamically during the data table editing operations or as a result of dynamically re-arranging table columns order.

Better solution

Better solution shown in the following Listing 2 effectively resolves all of those potential issues described above by using named DataKeys in GridView1 control to be used as a "foreign keys" for second DataSource. In this particular example, DataKey “Composer” is added to DataKeys in GridView1 control (requires the line DataKeyNames="Composer") to be passed to corresponding select parameter s.SelectParameters[0].DefaultValue of second DataSource named “dsMusic”.

Listing 2. Improved version using DataKeys

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e) {
  if (e.Row.RowType == DataControlRowType.DataRow)
   {
     // find DataSource used for nested GridView (could be SqlDataSource)
     AccessDataSource s = (AccessDataSource)e.Row.FindControl("dsMusic");
     // assign parameter’s default value from the DataKeys in GridView1
     s.SelectParameters[0].DefaultValue = Convert.ToString(((GridView)sender).DataKeys[e.Row.RowIndex].Values["Composer"]);
   }
}

Note: Listing 2 demonstrates the use of ASP.NET AccessDataSource, but the concept/usage is pretty much identical to SqlDataSource.

Sample Demo

Online Music Library with attached YouTube player [2-4] is implemented using the nested GridView techniques described above: click the image below to see the working demo:

Performance Improvement

Significant performance improvement could be achieved by enabling caching for nested DataSources and using FilterParameters instead of SelectParameters. To do so:

1. Set the nested DataSource attributes; FilterExpression="Composer ='{0}'" EnableCaching="True"
2. Modify the event procedure in Listing 2 by replacing the line assigning SelectParameters with the following one:
   

   // assign filter parameter default value from the datakey
   s.FilterParameters[0].DefaultValue = Convert.ToString(((GridView)sender).DataKeys[e.Row.RowIndex].Values["Composer"]);

... and voila (that's it!)

References

1. Walkthrough: Creating a Nested GridView Control[^]
2. Music Library implemented as nested GridView controls [^]
3. YouTube™ API for ASP.NET[^]
4. YouTube™ Embedded Video Player: Extended API (C#)[^]