Setting the Initial Sort Order – Dynamic Data

This is just a quick note on a post I made on the Dynamic Data Forum to answer a question where setting the DisplayColumnAttribute should set the default sort order of the GridView on the List page but didn’t. Here’s how I solved it with a hint or two from Marcin Dobosz.

[MetadataType(typeof(Orders_Metadata ))]
[DisplayColumn("OrderID", "OrderID", true)]
public partial class Orders
{
    public class Orders_Metadata
    {       
        // ...
    }
}

Listing 1 – Example Metadata

Assuming you have a table with the DisplayColumnAttribute set you could put this on your List page: 

table = GridDataSource.GetTable();

// set default sort
if (!IsPostBack && table.SortColumn != null)
    GridView1.Sort(table.SortColumn.Name, table.SortDescending ? SortDirection.Descending : SortDirection.Ascending);

Listing 2 – Add to Page_Init (.Net 3.5)

// set default sort
if (!IsPostBack && table.SortColumn != null)
{
    var order = new OrderByExpression()
    {
        DataField = table.SortColumn.Name,
        Direction = table.SortDescending ? SortDirection.Descending : SortDirection.Ascending,
    };
    GridQueryExtender.Expressions.Add(order);
}

Listing 3 – Add to Page_Init (.Net 4)

public static T GetAttribute<T>(this MetaTable table) where T : Attribute
{
    return table.Attributes.OfType<T>().FirstOrDefault();
}

Listing 3 – you will also need this extension method see Writing Attributes and Extension Methods for Dynamic Data

Add your DisplayColumnAttribute (see Listing 1) to the table you want sorted (note: it must have the second string constant even if it’s the same name, as the second string it the one that the sort is done on, and the third value if true causes the sort to be descending). Then in Listing 2 you get the attribute using the extension method from Listing 3 and apply the relevant sort.

This is here mainly so I can find it again!