Customising the LinqDataSource

Binding a data grid to a data source quickly is a sinch with a LinqDataSource and it can save a lot of time. However sometimes it doesn't quite cut it and you wished you could use all of its benefits but just change one little aspect. Well actually with a bit of tweaking you can do exactly that. Here are two cases that I've frequently used while building some quick prototypes.

Altering the fields that are sent to a LinqDataSource

The data that is sent or received for a LinqDataSource action may need to be altered for a number of reasons, such as:

1. Altering the data sent in an update if the information is incorrect (e.g. a blank ("") field updating to a numerical field)
2. Filling in extra information for an insert (e.g. a predetermined foreign key)

The code is implemented in the handler for the LinqDataSource action, this will either be Inserting, Updating, or Deleting as the event will need to happen prior to the action.  In the code, first create a variable of the table type, then select the specific field and change it as needed.

Altering an Insert Example:

In this case, a foreign key needs to be automatically filled in.  The foreign key is taken from the query string parameter of the URL.

Protected Sub LinqDataSource_Inserting(sender As Object, e As System.Web.UI.WebControls.LinqDataSourceInsertEventArgs) Handles LinqDataSource.Inserting

    Dim rec As WEB_Table = e.NewObject

    Dim field As String = Request.QueryString("Field")

    If rec IsNot Nothing Then

        rec.Field = field

    End If

End Sub


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Using a Stored Procedure or more complicated query with a LinqDataSource

Sometimes you want to use all the handiness of the automated Insert, Update and Delete functions but use a select command that is too complicated to be handled by the basic features provided by the LinqDataSource control. In order to do this we just override the Select query in the Selecting event. Here is an example of how to inject a stored procedure as the select data source.

1. Create stored procedure for your SELECT that includes any other business logic you want in it
2. Add the stored procedure to the data context and if you want to turn off optimistic concurrency checks, set Update Check to Never for all properties in that table (can highlight them all to change all at once)
3. In code behind change Selecting event of LinqDataSource to set the e.Result = DC.StoredProcedure(Params).ToList()

Protected Sub lds_Selecting(sender As Object, e As System.Web.UI.WebControls.LinqDataSourceSelectEventArgs) Handles lds.Selecting
    Dim res = db.usp_StoredProcList(Param1, e.WhereParameters("ParentID")).ToList()
    e.Result = res
End Sub

4. Remove any Where clause from LinqDataSource (and any WhereParameters if you don't need them)
5. Use WhereParameter to get ParentID field into Selecting event for Detail Level tables - accessed via e.WhereParameters("ParentID")