Part 3 – A Cascading Hierarchical Field Template & Filter for Dynamic Data

• Part 1 – The Read-Only Hierarchical Field Template
• Part 2 – The Edit Hierarchical Field Template
• Part 3 – The Basic Hierarchical Filter

This would have been the final part of the series of articles, however I realised that we will need a final article that covers the more complex action of the CascadingHierarchicalFilter, this where at each level of selection we filter the list.

Figure 1 – Cascading Hierarchical Filter.

e.g. in Figure 1 the CascadingHierarchicalFilter (the basic version) no selection occurs until we select a value from the final list control, however in the complex CascadingHierarchicalFilter we will filter at each level and so we will hold that over until we have completed the basic version of the CascadingHierarchicalFilter.

And so to the basic version, first we will need a starting place so copy the ForeignKey filter and rename it to CascadingHierarchical and the class name to CascadingHierarchicalFilter. Next we remove the content of the aspx page so it looks like Listing 1.

<%@ Control 
    Language="C#" 
    CodeBehind="CascadeHierarchical.ascx.cs" 
    Inherits="CascadeHierarchicalFieldTemplate.CascadeHierarchicalFilter" %>

Listing 1 – CascadingHierarchical.aspx page

Then we start on the code behind by adding our member variables, adjusting the two properties and replacing the default Page_Init with ours, which is very similar to the Edit templates Page_Init see Listing 2.

#region member variables
private const string NullValueString = "[null]";
// hold the current data context to access the model
private object context;
// hold the list of filters
private SortedList<int, HierachicalListControl> filters = new SortedList<int, HierachicalListControl>();
// hold the attribute
private CascadeHierarchicalAttribute cascadeHierarchicalAttribute;
#endregion

private new MetaForeignKeyColumn Column
{
    get { return (MetaForeignKeyColumn)base.Column; }
}

public override Control FilterControl
{
    get
    {
        if (filters[0] != null && filters[0].ListControl != null)
            return filters[0].ListControl;
        else
            return null;
    }
}

protected void Page_Init(object sender, EventArgs e)
{
    //if (!Column.IsRequired)
    // check we have a cascade hierarchical attribute if not throw error
    cascadeHierarchicalAttribute = Column.GetAttribute<CascadeHierarchicalAttribute>();
    if (cascadeHierarchicalAttribute == null)
        throw new InvalidOperationException("Was expecting a CascadeFilterAttribute.");

    // check we have correct column type if not throw error
    if (!(Column is MetaForeignKeyColumn))
        throw new InvalidOperationException(String.Format("Column {0} must be a foreign key column navigation property", Column.Name));

    // get current context
    context = Column.Table.CreateContext();

    // get hierarchical cascade columns
    var parentColumns = new SortedList<int, String>();
    for (int i = 0; i < cascadeHierarchicalAttribute.Parameters.Length; i++)
        parentColumns.Add(i, cascadeHierarchicalAttribute.Parameters[i]);

    // add extra column to represent this column itself
    parentColumns.Add(cascadeHierarchicalAttribute.Parameters.Length, String.Empty);

    //get current column into a local variable
    MetaForeignKeyColumn currentColumn = Column;

    // setup list of filter definitions
    for (int i = 0; i < parentColumns.Count; i++)
    {
        // get parent column name
        var parentColumnName = parentColumns[i];

        // create dropdown list
        var ddl = new DropDownList()
        {
            ID = String.Format("ListControl{0}", i),
            Enabled = false,
            AutoPostBack = true
        };

        // create filter
        var filter = new HierachicalListControl(ddl) { Column = currentColumn };

        // check for last parent filter
        if (!String.IsNullOrEmpty(parentColumnName))
        {
            // set parent column from parent table
            filter.ParentColumn = (MetaForeignKeyColumn)currentColumn.ParentTable.GetColumn(parentColumnName);

            // set current column to parent column
            currentColumn = filter.ParentColumn;
        }
        else
        {
            // this is the last parent and has
            // no parent itself so set to null
            filter.ParentColumn = null;
            currentColumn = null;
        }
        // add filter to list of filters
        filters.Add(i, filter);
    }

    // add dropdown list to page in correct order 2, 1, 0
    // last parent, parent<N>, child
    for (int i = parentColumns.Count - 1; i >= 0; i--)
    {
        // setup dropdown list
        filters[i].ListControl.Items.Clear();
        filters[i].ListControl.Items.Add(new ListItem("------", String.Empty));

        // add parent list controls event handler
        if (i > 0)
            filters[i].ListControl.SelectedIndexChanged += ListControls_SelectedIndexChanged;
        else
            filters[i].ListControl.SelectedIndexChanged += ListControl0_SelectedIndexChanged;

        // add control to place holder
        this.Controls.Add(filters[i].ListControl);
    }

    if (DefaultValue != null)
        PopulateAllListControls(DefaultValue);
    else
    {
        // fill last parent filter
        var lastParentIndex = filters.Count - 1;
        var parentTable = filters[lastParentIndex].Column.ParentTable;
        var parentQuery = parentTable.GetQuery(context);

        // set next descendant list control
        PopulateListControl(lastParentIndex, parentQuery);
    }
}

Listing 2 – Member variables and Page_Init

Now we add the following Listings 3 & 4 these are virtually the same as from the Edit template and so I am thinking in the next revision they may all be removed to the class library.

/// <summary>
/// Sets the default values.
/// </summary>
/// <param name="fieldValue">The value.</param>
private void PopulateAllListControls(object fieldValue)
{
    var displayStrings = new SortedList<int, String>();

    #region Get list of propert values
    // get property values
    var propertyValues = new SortedList<int, Object>();
    propertyValues.Add(0, fieldValue);
    for (int i = 0; i < filters.Count - 1; i++)
    {
        var parentName = filters[i].ParentColumn.Name;
        object pv = propertyValues[i].GetPropertyValue(parentName);
        propertyValues.Add(i + 1, pv);
    }
    #endregion

    // stating at the first filter and work way up to the last filter
    for (int i = 0; i < filters.Count; i++)
    {
        var parentTable = filters[i].Column.ParentTable;
        var parentQuery = parentTable.GetQuery(context);
        IQueryable listItemsQuery;
        if (i == cascadeHierarchicalAttribute.Parameters.Length)
        {
            listItemsQuery = parentQuery.GetQueryOrdered(parentTable);
        }
        else
        {
            var pcol = filters[i + 1].Column;
            var selectedValue = filters[i].ParentColumn.GetForeignKeyString(propertyValues[i]);
            listItemsQuery = parentQuery.GetQueryFilteredFkColumn(pcol, selectedValue);
        }

        // set next descendant list control
        PopulateListControl(i, listItemsQuery);

        // set initial values
        var selectedValueString = filters[i].Column.Table.GetPrimaryKeyString(propertyValues[i]);
        ListItem item = filters[i].ListControl.Items.FindByValue(selectedValueString);
        if (item != null)
            filters[i].ListControl.SelectedValue = selectedValueString;
    }
}

Listing 3 – PopulateAllListControls

/// <summary>
/// Handles the SelectedIndexChanged event of the parentListControls control.
/// </summary>
/// <param name="sender">The source of the event.</param>
/// <param name="e">
/// The <see cref="System.EventArgs"/> instance containing the event data.
/// </param>
/// <summary>
/// Setups the parent list control.
/// </summary>
/// <param name="table">The table.</param>
/// <param name="filterIndex">The parent id.</param>
/// <param name="items">The items.</param>
public void PopulateListControl(int filterIndex, IQueryable items)
{
    // clear the list controls list property
    filters[filterIndex].ListControl.Items.Clear();
    // enable list control
    filters[filterIndex].ListControl.Enabled = true;

    // add unselected value showing the column name
    // [Styles]
    filters[filterIndex].ListControl.Items.Add(
        new ListItem(String.Format("[{0}]",
            filters[filterIndex].Column.DisplayName), NullValueString));

    foreach (var row in items)
    {
        // populate each item with the display string and key value
        filters[filterIndex].ListControl.Items.Add(
            new ListItem(filters[filterIndex].Column.ParentTable.GetDisplayString(row),
            filters[filterIndex].Column.ParentTable.GetPrimaryKeyString(row)));
    }
}

/// <summary>
/// Resets all descendant list controls.
/// </summary>
/// <param name="startFrom">The start from.</param>
private void ResetAllDescendantListControls(int startFrom)
{
    for (int i = startFrom - 1; i >= 0; i--)
    {
        filters[i].ListControl.Items.Clear();
        filters[i].ListControl.Items.Add(new ListItem("----", String.Empty));
        filters[i].ListControl.Enabled = false;
    }
}

Listing 4 – PopulateListControl and ResetAllDescendantListControls

Listing 5 is again virtually the same as the Edit templates but I kept it separate as it is an event handler and may make more sense to keep it in the template.

/// <summary>
/// Handles the SelectedIndexChanged event for each List control, 
/// and populates the next list control in the hierarchy.
/// </summary>
/// <param name="sender">The source of the event.</param>
/// <param name="e">
/// The <see cref="System.EventArgs"/> instance containing the event data.
/// </param>
void ListControls_SelectedIndexChanged(object sender, EventArgs e)
{
    // get list control
    var listControl = (ListControl)sender;

    // get the sending list controls id as an int
    var id = ((Control)sender).ID;

    // use regular expression to find list control index
    var regEx = new Regex(@"\d+");
    var parentIndex = int.Parse(regEx.Match(id).Value);

    if (listControl.SelectedValue != NullValueString)
    {
        if (parentIndex > 0)
        {
            // set child index
            var childIndex = parentIndex - 1;

            // get parent table
            var parentTable = filters[childIndex].Column.ParentTable;

            // get query from table
            var query = parentTable.GetQuery(context);

            // get items for list control
            var itemQuery = query.GetQueryFilteredFkColumn(
                filters[parentIndex].Column,
                listControl.SelectedValue);

            // populate list control
            PopulateListControl(childIndex, itemQuery);

            // reset all descendant list controls
            ResetAllDescendantListControls(childIndex);
        }
    }
    else
    {
        // reset all descendant list controls
        ResetAllDescendantListControls(parentIndex);
    }
}

Listing 5 – ListControls_SelectedIndexChanged

Next we replace the DropDownList1_SelectedIndexChanged with ListControl0_SelectedIndexChanged Listing 6 really only a name change to make the code read clearly.

protected void ListControl0_SelectedIndexChanged(object sender, EventArgs e)
{
    OnFilterChanged();
}

Listing 6 – ListControl0_SelectedIndexChanged

Finally we need to change the GetQueryable method to replace DropDownList1 with filters[0].ListControl.

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Happy coding

Note: With a few changes around the last two listings you could adapt this to either the old Dynamic Data Futures VS2008 SP1 RTM filters on CodePlex or Josh Heyes’s Dynamic Data Filtering.