C# example with and without ORM

With_ORM.cs

/* 
Very simple example using LINQ to SQL and based on the MSDN LINQ to SQL page.
Make sure you include System.Data.Linq and System.Data.Linq.Mappings in your usings.
*/

// Table you want to associate with the entity
[Table(Name="Customer")]
public class Customer
{
    // Columns in the database. Should have the same name between database and class variable
    [Column(IsPrimaryKey = true)]
    public int row_id { get; set; }

    [Column]
    public string Name { get; set; }

    [Column]
    public int Age { get; set; }

}

// This is essentially the connection to your database. It handles generating SQL statements and
// creating objects out of those SQL statements (if they are queries)
public class MyDatabase : DataContext
{
    public Table<Customer> customerTable;
    public MyDatabase(string connection) : base(connection) { }
}

// This actually retrieves the data for you. Look how short and sweet it is after setting up the above!
public static class DBHelper
{
    public static List<Customer> RetrieveAllCustomers()
    {
        MyDatabase db = new MyDatabase(GetConnectionString());

        var customers = db.customerTable.Select(row => row);
        
        /* Alternatively (This translates to the above statement):
         * var customers = from row in db.customerTable
         *                 select row;
         */

        return customers.ToList();
    }
}

Without_ORM.cs

public class Customer
{
    public string Name { get; set; }
    public int Age { get; set; }
    public int row_id { get; set; }
}

public static class DBHelper
{
    public static List<Customer> RetrieveAllCustomers()
    {
        DataTable data = new DataTable();
        List<Customer> customers = new List<Customer>();
        
        using (SqlConnection conn = new SqlConnection(GetConnectionString()))
        {
            conn.Open();
            if (conn.State == ConnectionState.Open)
            {
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = "SELECT name, age, row_id FROM customer";
                    
                    DataReader reader = cmd.ExecuteReader();
                    data.Load(reader);   
                    
                    foreach (DataRow row in data.Rows)
                    {
                        customers.Add(new Customer { Name = row.Field<string>("NAME"), Age = row.Field<int>("AGE"), row_id = row.Field<int>("ROW_ID")});
                    }
                }
            }
        }
            
        return customers;
    }
}