How to reduce the filter options in radgrid as more filters are applied

Question

Within my RadGrid I'm using FilterType="Combined" and I am binding the filter drop down using the FilterCheckListItemsRequested method. My code looks like the following:

protected void rgCallRecordings_FilterCheckListItemsRequested(object sender, GridFilterCheckListItemsRequestedEventArgs e)
    {
        // Get the list of calls stored in session
        var results = (IQueryable<DC_CR_RECORDING>)Session["CallRecordings"];

        // Get the column name
        string dataField = (e.Column as IGridDataColumn).GetActiveDataField();

        // Get the filter expression of the grid
        string filterExpression = rgCallRecordings.MasterTableView.FilterExpression;

        // Initialise new list
        IEnumerable<DC_CR_RECORDING> DistinctList = new List<DC_CR_RECORDING>();            

        // Depending on which column it is change the data output.
        switch (dataField)
        {
            case "SCRIPT_AGENT":
                // Seperate the script agents from the call recordings
                DistinctList = results.GroupBy(s => s.SCRIPT_AGENT).Select(group => group.First());                    
                break;
            case "CLIENT_NAME":
                // Seperate the Client name from the call recordings
                DistinctList = results.GroupBy(s => s.CLIENT_NAME).Select(group => group.First());
                break;
            case "CLIENT_REF_NUMBER":
                // Seperate the Client name from the call recordings
                DistinctList = results.GroupBy(s => s.CLIENT_REF_NUMBER).Select(group => group.First());
                break;
            case "CLIENT_LINK_REF":
                // Seperate the Client link reference from the call recordings
                DistinctList = results.GroupBy(s => s.CLIENT_LINK_REF).Select(group => group.First());
                break;
            case "SCRIPT_TYPE":
                // Seperate the call direction from the call recordings
                DistinctList = results.GroupBy(s => s.SCRIPT_TYPE).Select(group => group.First());
                break;
            case "SCRIPT_RESULT":
                // Seperate the call direction from the call recordings
                DistinctList = results.GroupBy(s => s.SCRIPT_AGENT).Select(group => group.First());
                break;
        }

I am trying to update the filter options every time a new filter is applied so the list of options only displays items which are present in the filtered grid. I have tried getting the filter expression when a filter is applied but I am unsure how to apply this to the results set.

Answer 1

Instead of using the filter expression of the rad grid I decided to use a different approach and use the current data in the rad grid itself when a filter is applied:

        // If there is a filter applied then enter the loop if there isn't then the filter expression will be empty 
        if (!String.IsNullOrEmpty(filterExpression))
        {                
            // Create a new list of strings to hold the sequence ids
            List<string> sequenceIds = new List<string>();

            // For each row in the radgrid...
            foreach (GridDataItem row in rgCallRecordings.Items) // loops through each rows in RadGrid
            {
                // ...Add the sequence id to the list
                sequenceIds.Add(row.GetDataKeyValue("SEQUENCE_ID").ToString());                    
            }
            // Only return results whose sequence ids are in the list
            results = results.Where(a => sequenceIds.Contains(a.SEQUENCE_ID));                
        }    

The method as a whole now looks like this:

protected void rgCallRecordings_FilterCheckListItemsRequested(object sender, GridFilterCheckListItemsRequestedEventArgs e)
    {
        // Get the list of calls stored in session
        var results = (IQueryable<DC_CR_RECORDING>)Session["CallRecordings"];

        var listResults = results.ToList();
        // Get the column name
        string dataField = (e.Column as IGridDataColumn).GetActiveDataField();

        // Get the filter expression of the grid to determine if there is
        string filterExpression = rgCallRecordings.MasterTableView.FilterExpression;

        // Initialise new list
        IEnumerable<DC_CR_RECORDING> DistinctList = new List<DC_CR_RECORDING>();

        // If there is a filter applied then enter the loop if there isn't then the filter expression will be empty 
        if (!String.IsNullOrEmpty(filterExpression))
        {                
            // Create a new list of strings to hold the sequence ids
            List<string> sequenceIds = new List<string>();

            // For each row in the radgrid...
            foreach (GridDataItem row in rgCallRecordings.Items) // loops through each rows in RadGrid
            {
                // ...Add the sequence id to the list
                sequenceIds.Add(row.GetDataKeyValue("SEQUENCE_ID").ToString());                    
            }
            // Only return results whose sequence ids are in the list
            results = results.Where(a => sequenceIds.Contains(a.SEQUENCE_ID));                
        }            

        // Depending on which column it is change the data output.
        switch (dataField)
        {
            case "SCRIPT_AGENT":
                // Seperate the script agents from the call recordings
                DistinctList = results.GroupBy(s => s.SCRIPT_AGENT).Select(group => group.First());                    
                break;
            case "CLIENT_NAME":
                // Seperate the Client name from the call recordings
                DistinctList = results.GroupBy(s => s.CLIENT_NAME).Select(group => group.First());
                break;
            case "CLIENT_REF_NUMBER":
                // Seperate the Client name from the call recordings
                DistinctList = results.GroupBy(s => s.CLIENT_REF_NUMBER).Select(group => group.First());
                break;
            case "CLIENT_LINK_REF":
                // Seperate the Client link reference from the call recordings
                DistinctList = results.GroupBy(s => s.CLIENT_LINK_REF).Select(group => group.First());
                break;
            case "SCRIPT_TYPE":
                // Seperate the call direction from the call recordings
                DistinctList = results.GroupBy(s => s.SCRIPT_TYPE).Select(group => group.First());
                break;
            case "SCRIPT_RESULT":
                // Seperate the call outcome from the call recordings
                DistinctList = results.GroupBy(s => s.SCRIPT_RESULT).Select(group => group.First());
                break;
        }

        RadListBoxItem rlbItem = new RadListBoxItem();

        // Bind the filter list box with the results corresponding to which column the user selected
        e.ListBox.DataSource = DistinctList;
        e.ListBox.DataKeyField = dataField;
        e.ListBox.DataTextField = dataField;
        e.ListBox.DataValueField = dataField;
        e.ListBox.DataBind();

    }

The filters now update everytime a new filter is applied.