What is a more general way of creating an arraylist in C# like the one in the example?

Question

Objective: Achieve a more general way of creating an arraylist.

Issue: I have to create multiple arraylists, each matched to a unique structure for the purpose of comparing and updating a table in Sql database. In the spirit of DRY I am trying to find a better way of creating each array. The code I am using is as follows

Sample Code:

using System;  
using System.Collections.Generic;  
using System.Linq;  
using System.Text;  
using System.Diagnostics;  
using System.Data;  
using System.Data.SqlClient;  
using System.Collections;  
using System.Configuration;  

public static void Users()
{
    String sql = "";

    try
    {

         conn.Open();

         sql = "SELECT" +
                   "database.dbo.table1.username," +
                   "database.dbo.table1.status"   +
               "FROM" +
                   "database.dbo.table1";
         SqlCommand cmd = new SqlCommand(sql, conn);

         SqlDataReader dr = cmd.ExecuteReader();

         while (dr.Read())
         {
              //structure below
              User structure_A = new User();

              structure_A.username = dr.GetValue(0).ToString();
              structure_A.status   = dr.GetValue(1).ToString();

              //added to arraylist
              arraylist_A.Add(structure_A);
          }

          dr.Close();
          conn.Close();
}

Note: More information can be provided as requested. Thank you in advance for any insight

Answer 1

One thing you can do is create a generic method that takes the parameters that differ. For example:

public static ArrayList LoadInfo<T>(string sql, Func<SqlDataReader, T> getItem) where T: new
{
    var list = new ArrayList();
    conn.Open();
    SqlCommand cmd = new SqlCommand(sql, conn);
    SqlDataReader dr = cmd.ExecuteReader();
    while (dr.Read())
    {
        list.Add(getItem(dr));
    }
    return list;
}

public static User LoadUser(SqlDataReader dr)
{
    User structure_A = new User();
    structure_A.username = dr.GetValue(0).ToString();
    structure_A.status   = dr.GetValue(1).ToString();
    return User;
}

Now, to call it to load users, you just pass it the SQL query and the LoadUser method:

string usersQuery = "SELECT ....";  // select users query
ArrayList usersList = LoadInfo(usersQuery, LoadUser);

And if you need to load a bunch of Fooby objects, you'd create the Fooby query and a LoadFooby method that can create and populate a Fooby from the data row.

I'd suggest that you look into using List rather than ArrayList.

Answer 2

You could solve the problem with generics and using reflection to find out what the structure looks like. But I would recommend looking in to Entity Framework instead.

There is a good introduction to using EF Database first here: http://msdn.microsoft.com/en-us/data/jj200620