C# Bits: January 2013

Well this is the first post of 2013 and has been brewing for a while, what we want is to be able to set the initial sort of the GridView on the List page or ListDetails page. Listing 1 shows what we want to achieve.

OrderDate sorted Descending and ShipName sorted Ascending

Figure 1 – OrderDate sorted Descending and ShipName sorted Ascending

The Multi Column Sort Attribute

Figure 2 shows the first version of the attribute, I was using magic strings. But in Figure 3 we have an enum from System.Web.UI.WebControls to help us out (I’m a bad speller and I tend to type too quickly) so I think that is better.

Early Version Of Metadata

Figure 2 – Early Version Of Metadata

Example Metadata

Figure 3 – Example Metadata

Listing 1 shows the MultiColumnSortAttribute I am using the params construct to get a list of values from the attribute and I am using the BuildColumnParametersDictionary method to convert the object array to a dictionary with a string key the column name and a value of the SortDirection.

[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
public class MultiColumnSortAttribute : Attribute
{
    private IDictionary<String, SortDirection> _columns;

    public IDictionary<String, SortDirection> Columns
    {
        get { return this._columns; }
    }

    public MultiColumnSortAttribute(params object[] columnParameters)
    {
        _columns = BuildColumnParametersDictionary(columnParameters);
    }

    private IDictionary<String, SortDirection> BuildColumnParametersDictionary(object[] objArray)
    {
        var dictionary = new Dictionary<String, SortDirection>();
        if ((objArray != null) && (objArray.Length != 0))
        {
            if ((objArray.Length % 2) != 0)
                throw new InvalidOperationException(
                    String.Format("Need even number of control parameters.", 
                    new object[0]));

            for (int i = 0; i < objArray.Length; i += 2)
            {
                if (objArray[i] is String && objArray[i + 1] is SortDirection)
                {
                    if (objArray[i] == null)
                        throw new InvalidOperationException(
                            String.Format("Column name [{0}] is null.", i));

                    // get column name from array
                    String columnName = objArray[i] as String;
                    if (columnName == null)
                        throw new InvalidOperationException(
                            String.Format("Column name '{0}' is not a String.", 
                            objArray[i].ToString()));

                    // check for duplicate column names
                    if (dictionary.ContainsKey(columnName))
                        throw new InvalidOperationException(
                            String.Format("Column name '{0}' occurs more than once.", 
                            columnName));

                    // get sort direction from array
                    if (objArray[i + 1] == null)
                        throw new InvalidOperationException(
                            String.Format("Sort direction '{0}' is not a of type SortDirection.", 
                            objArray[i].ToString()));

                    SortDirection sortDirection = (SortDirection)objArray[i + 1];
                    dictionary[columnName] = sortDirection;
                }
            }
        }
        return dictionary;
    }
}

Listing 1 - MultiColumnSortAttribute

An Extension Method to Add Multi Column Sort to the Page

This extension method in Listing 2 is a little more complicated than it would need to be to handle just the Multi Column Sort, it also handles the DisplayColumn attribute to, this way we cover all bases.

Note: The GetAttribute<T>() extension method is covered here Writing Attributes and Extension Methods for Dynamic Data

/// <summary>
/// Sets the initial sort order.
/// </summary>
/// <param name="queryExtender">The query extender.</param>
/// <param name="table">The table.</param>
public static void SetInitialSortOrder(this QueryExtender queryExtender, MetaTable table)
{
    var multiColumnSort = table.GetAttribute<MultiColumnSortAttribute>();
    if (multiColumnSort != null)
    {
        var firstEntry = multiColumnSort.Columns.Keys.First();
        var order = new OrderByExpression()
        {
            DataField = firstEntry,
            Direction = multiColumnSort.Columns[firstEntry],
        };

        foreach (var item in multiColumnSort.Columns)
        {
            if (item.Key != firstEntry)
            {
                order.ThenByExpressions.Add(new ThenBy()
                {
                    DataField = item.Key,
                    Direction = item.Value
                });
            }
        }
        queryExtender.Expressions.Add(order);
    }
    else if (table.SortColumn != null)
    {
        var order = new OrderByExpression()
        {
            DataField = table.SortColumn.Name,
            Direction = table.SortDescending ? SortDirection.Descending : SortDirection.Ascending,
        };
        queryExtender.Expressions.Add(order);
    }
}

Listing 2 – SetInitialSortOrder Extension Method

Using in the List Page Template

All we need to do in the List and ListDetails page templates is to add one line to the Page_Init method.

protected void Page_Init(object sender, EventArgs e)
{
    table = DynamicDataRouteHandler.GetRequestMetaTable(Context);
    GridView1.SetMetaTable(table, table.GetColumnValuesFromRoute(Context));
    GridDataSource.EntityTypeFilter = table.EntityType.Name;

    // set initial sort order
    GridQueryExtender.SetInitialSortOrder(table);
}

Listing 3 – adding the extension method to the Page Template