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I have a problem with my MVC Asp.Net. I created the Connection String inside Webconfig,
<connectionStrings>
    <add name="connSql"
    providerName="System.Data.SqlClient"
    connectionString="Data Source=localhost;
          Initial Catalog=CarnetAdresse;
          Integrated Security=True" />
  </connectionStrings>then created the Getlist() method within the "Contact" Template to bring the database list :
 public static List<Contact> GetList()
        {
            string connexionSql = ConfigurationManager.ConnectionStrings["connSql"].ConnectionString;
            using (SqlConnection cnx = new SqlConnection(connexionSql))
            {
                string requete = "SELECT * FROM Contact";
                SqlCommand cmd = new SqlCommand(requete, cnx);
                cmd.CommandType = System.Data.CommandType.Text;
                try
                {
                    cnx.Open();
                    SqlDataReader dataReader = cmd.ExecuteReader();
                    List<Contact> contactList = new List<Contact>();
                    while (dataReader.Read())
                    {
                        Contact c = new Contact();
                        c.id = (int)dataReader["id"];
                        c.Nom = (string)dataReader["Nom"];
                        c.Telephone = (string)dataReader["Telephone"];
                        c.Courriel = (string)dataReader["Courriel"];
                        c.DateNaissance = (DateTime)dataReader["DateNaissance"];
                        c.CodePostal = (string)dataReader["CodePostal"];
                        contactList.Add(c);
                    }
                    dataReader.Close();
                    return contactList;
                }
                finally
                {
                    cnx.Close();
                }
            }
        }and he gives me an Exception every time I try to run the program:
Une Exception de type 'System.Nullreferenceexception' s'est produite dans Carnetadresse.dll mais n'a pas été gérée dans le code utilisateur
Informations supplémentaires : Object Reference not set to an instance of an Object.

Detail: Use Sqlserver 2012. On the teacher’s computer he used SQLEXPRESS and it worked, but in my nothing to work. I have deleted the created database other times, already modified the names of the connection string, rewrote the code... and nothing yet
– Marcelo Medeiros dos Santos
Another thing I tried: I added a rule in Windows Firewall to allow port 1433 for SQL SERVER. Firewall allow port 1433 for SQL Server Link: https://blogs.technet.microsoft.com/danstolts/2011/06/how-to-open-firewall-port-1433-for-sql-server-database-engine-for-use-with-scom-or-thinanyg-else/
– Marcelo Medeiros dos Santos