Generic sorting of customer objects for ObjectDataSource (ASP.NET)

Introduction

The class PropertyComparer provides the possibility for data-access-components to enable sorting for customer objects when using an ObjectDataSource.

Background

ASP.NET 2.0 includes the controls GridView and ObjectDataSource. You can define which methods of your data-access-component is used by the ObjectDataSource. If the Select method returns a DataSet or a DataTable, you can use paging and sorting for the GridView out of the box.

If you want to work with collections of business-objects instead of DataSet/DataTable, you have to implement the sorting yourself. I wrote a generic comparer for use with all my business-objects.

Using the code

Use a GridView where you define the DataSourceId, and enable sorting:

<asp:GridView     ID="exampleGridView" runat="server" 
        DataSourceID="exampleDataSource" 
        AllowSorting="True" ... >

Define the ObjectDataSource:

<asp:ObjectDataSource     ID="exampleDataSource" runat="server" 
            TypeName="ExampleDataAccessComponent" 
            SelectMethod="Select" 
            SortParameterName="orderBy" ... >

Write your data-access-component implementing the Select method:

[DataObject()]
public sealed class ActivityDac
{
    private string myConnectionString;
    private DbProviderFactory myFactory;


    public ActivityDac()
    {
        ConnectionStringSettings cs = 
           ConfigurationManager.ConnectionStrings[" ... "];
        myFactory = DbProviderFactories.GetFactory(cs.ProviderName);
        myConnectionString = cs.ConnectionString;
    }


    [DataObjectMethod(DataObjectMethodType.Select, true)]
    public Activity[] Select(string orderBy)
    {
        List<BusinessClass> list = new List<BusinessClass>();
        using (DbConnection con = myFactory.CreateConnection())
        {
            con.ConnectionString = myConnectionString;
            using (DbCommand cmd = myFactory.CreateCommand())
            {
                cmd.Connection = con;
                cmd.CommandText = " ... ";

                DbParameter p = myFactory.CreateParameter();
                ...
                cmd.Parameters.Add(p);

                con.Open();
                DbDataReader reader = cmd.ExecuteReader(CommandBehavior.SingleResult);

                while (reader.Read())
                {
                    BusinessClass o = new BusinessClass(reader.GetInt32(0));
                    ..
                    list.Add(o);
                }
            }
        }

        if (!String.IsNullOrEmpty(orderBy))
        {
            PropertyComparer<BusinessClass> comparer = 
              new PropertyComparer<BusinessClass>(orderBy);
            list.Sort(comparer);
        }

        return list.ToArray();
    }
}

Here is the code for the PropertyComparer:

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Collections;

namespace Example
{
    public class PropertyComparer<T> : IComparer<T>
    {
        private enum SortType
        {
            Descending = -1,
            Ascending = 1
        }


        private SortType mySortDirecton;
        private string mySortPropertyName;


        public PropertyComparer(string sortString)
        {
            if (sortString == null)
                throw new ArgumentNullException("sortString");
            if (sortString.Length == 0)
                throw new ArgumentOutOfRangeException("sortString");

            if (sortString.ToLower().EndsWith(" desc"))
            {
                mySortPropertyName = sortString.Substring(0, sortString.Length - 5);
                mySortDirecton = SortType.Descending;
            }
            else
            {
                if (sortString.ToLower().EndsWith(" asc"))
                    mySortPropertyName = sortString.Substring(0, sortString.Length - 4);
                else
                    this.mySortPropertyName = sortString;

                this.mySortDirecton = SortType.Ascending;
            }
        }


        #region IComparer<T> Members

        public int Compare(T x, T y)
        {
            if ((x == null) && (y == null))
                return 0;
            if (x == null)
                return -(int)mySortDirecton;
            if (y == null)
                return (int)mySortDirecton;

            PropertyInfo p = x.GetType().GetProperty(mySortPropertyName);
            if (p == null)
                throw new ApplicationException();

            object vX = p.GetValue(x, null);
            object vY = p.GetValue(y, null);

            if ((vX == null) && (vY == null))
                return 0;
            if (vX == null)
                return -(int)mySortDirecton;
            if (vY == null)
                return (int)mySortDirecton;

            return (int)mySortDirecton * Comparer.DefaultInvariant.Compare(vX, vY);
        }

        #endregion
    }
}