Linq to sql performance I'm creating a system and I'm using EF with Linq. I create my Model (.edmx) and using it, I generated my database and my classes. Like the Usuario (user in Portuguese going to keep the names in Portuguese to avoid some misleading).

namespace SistemaBox.Model
{
    public partial class Usuario
    {
        public int Codigo { get; set; }
        public string Nome { get; set; }
        public string Sobrenome { get; set; }
        public string Senha { get; set; }
        public DateTime DataCriacao { get; set; }
        public DateTime DataUltimoLogin { get; set; }

        public virtual PermissaoGrupo CodigoPermissaoGrupo { get; set; }
    }
}


After this, I create my controller class:

namespace SistemaBox.Controller
{
    [Serializable]
    public class ZUsuario : Usuario
    {
        String connString = ConfigurationManager.ConnectionStrings["ConnectionString"].ToString();

        /// &lt;summary&gt;
        /// Cadastro e edição
        /// &lt;/summary&gt;
        public void Cadastro()
        {
            if (Codigo != null &amp;&amp; Codigo &gt; 0)
            {
                // Cadastro
                using (DataContext db = new DataContext(connString))
                {
                    Table&lt;Usuario&gt; Usuarios = db.GetTable&lt;Usuario&gt;();
                    var query =
                        from usr in Usuarios
                        where usr.Nome == "Test"
                        select usr;

                    foreach (var usr in query)
                        Console.WriteLine("id = {0}, City = {1}", usr.Codigo, usr.Nome);
                }
            }
            else
            {
                // Edição

            }
        }
    }
}


Please ignore the fact that the class name is record and I'm doing a select. It is just for tests.

My question is about the controller. Is the right way to declare the connection String as global:

String connString = ConfigurationManager.ConnectionStrings["ConnectionString"].ToString();


and use the using like I'm doing?
Your connection string is actually a private class member. I would probably put private keyword explicitly to make it clear.

connString is going to be initialized each time the class instance is created. But the connection string is not going to change in run time so it worth to make connStrint a static member.