ADO_Query.cs

ADO_Query.cs

using (var connection = new SqlConnection(connectionString))
{
    connection.Open();
    using (var command = connection.CreateCommand())
    {
        command.CommandText = "SELECT Id, Name, ... FROM [dbo].[Customer];";
        var list = new List<Customer>();
        using (reader = command.ExecuteReader())
        {
            var customer = new Customer
            {
                Id = reader.GetInt32(0),
                Name = reader.GetString(1),
                ...
            };
            list.Add(customer);
        }
        return customer;
    }
}