ASP.NET 2.0 Resources

If you want custom paged and sortable ObjectDataSource you will have define some object properties (see the following ObjectDataSource declaration sample)...

<asp:ObjectDataSource 
    ID="FundListDataSource" 
    runat="server" 
    EnablePaging="True" 
    TypeName="Core.BLL.FundController" 
    SelectCountMethod="GetFundCount"     
    SelectMethod="GetFunds" 
    StartRowIndexParameterName="startrow" 
    MaximumRowsParameterName="maxrows"     
    SortParameterName="sortExpression" 
/>

ID, TypeName, runat and SelectMethod are probably familiar to you. So lets look at the others...

EnablePaging

This property turns on/off paging support for this data source. If you enable paging for ObjectDataSource control you also have to define SelectCountMethod, StartRowIndexParameterName and MaximumRowsParameterName properties.

SelectCountMethod

This property contains method name (must be static, parameterless method of TypeName type) used for geting total count of paged items.

StartRowIndexParameterName

This is the name of parameter for SelectMethod specifying starting page index.

MaximumRowsParameterName

Similar to StartRowIndexParameterName this parameter specifies how many rows to return.

SortParameterName

When using custom sorting for ObjectDataSource, this property contains name of the parameter that specifies row sorting.

This is my Bussiness Layer GetFuns method. It return list of all funds and has three parameters. First is starting data row, second is how many rows to return and the last one is our sorting expression. This method first tries to translate sortExpression from Bussiness Layer notation to Data layer notation (more about it later) and after that retrieves data from underlying Data layer.

public static List<FundInfo> GetFunds(int startrow, 
    int maxrows, string sortExpression)
{
    string translatedSortExpression = null;
    List<FundInfo> funds = null;

    if (!String.IsNullOrEmpty(sortExpression)) { 
        translatedSortExpression = 
            CBO<FundInfo>.TranslateSortParams(sortExpression);
    }

    using (IDataReader dr = 
        DataProviderFactory.CoreProvider.GetFunds(
                                startrow, 
                                maxrows, 
                                translatedSortExpression))
    {
        funds = CBO<FundInfo>.FillList(dr);
    }
    return funds;
}

Translating sortExpression to Data layer notation is quite tricky. Previously mentioned GetFunds method is used to populate web application GridView defined for example as...

<asp:GridView ID="GridView1" runat="server" 
    AllowPaging="True" AutoGenerateColumns="False"
    DataSourceID="FundListDataSource" AllowSorting="True">
    <Columns>
        <asp:BoundField DataField="ID" 
            HeaderText="ID" SortExpression="ID" />
        <asp:BoundField DataField="Name" 
            HeaderText="Name" SortExpression="Name" />
        <asp:BoundField DataField="ISIN" 
            HeaderText="ISIN" SortExpression="ISIN" />
    </Columns>
</asp:GridView>

The sort expressions comming from this Gridview are ID, Name and ISIN but Data Layer works internally with column names FND_ID, FND_NAME and FND_ISIN. Translation from one notation to another is handled by CBO's class static method TranslateSortParams. It uses reflection on FundInfo class properties which are decorated with DatabaseField atributes to translate from one notation to another.

As noted in original arcicles, for large result sets this custom paging is roughly two order of magnitudes faster than the default paging. It's implementation is not so straight forward as default paging and sorting but for large result sets together with correct database indexes it works like a charm. Definitely have a look at those arcticles too!