Custom Field in Crystal Report

using System;

using System.Reflection;
using System.Web;
using System.Threading;
using HMIS;
using System.Data;
using System.Collections.Specialized;
//using HMIS.Global.Providers;
//using HMIS.Global;
using HMIS.Main.Registration_Comm;
using System.Configuration;





namespace HMIS.Main.Registration_Comm {

    public abstract class RegistrationProvider 
    {
        #region Class Variables
        public abstract DataTable GetPatientsByRegDate(DateTime from, DateTime to);
        static RegistrationProvider _provider;
       // static CacheManager cache = null;
        #endregion

        #region Properties
        private DataSet _ds = null;

        public DataSet ds
        {
            get {
                return this._ds;
            }
            set {
                this._ds = value;
            }
        }
        #endregion
                       
        #region Instance Function
        public static RegistrationProvider Instance()
        {

             //Use the cache because the reflection used later is expensive
            //if(cache==null)
            //    cache = CacheFactory.GetCacheManager("MyCache1");

            Type type = null;
            string cacheKey = null;

            if (_provider == null)
            {
                string ss=System.Configuration.ConfigurationManager.ConnectionStrings["AdventureWorksDB"].ConnectionString;
                _provider=(RegistrationProvider)(new SqlRegistrationProvider(ss));
            }

            Configuration config=ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
            //config.AppSettings.Settings.Add(

            return _provider;

            // Get the names of the providers
            //RegistrationConfiguration config = RegistrationConfiguration.GetConfig();

            // Read the configuration specific information
            // for this provider
           // Provider registrationProvider = (Provider)config.Providers[config.DefaultProvider];

            // In the cache?
            //cacheKey = "Registration::" + config.DefaultProvider;
            //if (!cache.Contains(cacheKey)) {

            //    // The assembly should be in \bin or GAC, so we simply need
            //    // to get an instance of the type
            //    try {

            //        type = Type.GetType(registrationProvider.Type);

            //        // Insert the type into the cache
            //        Type[] paramTypes = new Type[1];
            //        paramTypes[0] = typeof(string);
            //        cache.Add(cacheKey, type.GetConstructor(paramTypes), CacheItemPriority.NotRemovable, null, null);
            //        //cache.Insert( cacheKey, type.GetConstructor(paramTypes) );

            //    } catch (Exception e) {
            //        throw new Exception("Unable to load Registration provider", e);
            //    }

            //}

            // Load the configuration settings
          //  object[] paramArray = new object[1];
        //    paramArray[0] = registrationProvider.Attributes["connectionString"];

         //   type = Type.GetType("HMIS.Main.Registration_Comm.SqlRegistrationProvider, SqlRegistrationProvider");
          //  Type[] paramTypes = new Type[1];
           // paramTypes[0] = typeof(string);
           // return (RegistrationProvider)(type.GetConstructor(paramTypes).Invoke(paramArray));

            

            //return (RegistrationProvider)(((ConstructorInfo)cache.GetData(cacheKey)).Invoke(paramArray));
        }
        #endregion

       

       

    }
}