Question

Trying to improve my C# to SQL skills… Currently I am using this bit of code to pull data from our application server. I have two different DBA’s telling me two other ways to write this, just trying to figure out if this should be improved on or changed. If so, I would really appreciate some kind of examples.

FYI: This code…

db.con(user.Authority)

…Is essentially a ‘new sqlconnection’ code.

DataTable dtInfo = new DataTable("SomeInfo");
using (SqlConnection con = db.con(user.Authority))
        {
            string command = "SOME SQL STATEMENT;";
            using (SqlCommand cmd = new SqlCommand(command,con))
            {
                cmd.CommandType = CommandType.Text;
                cmd.Parameters.AddWithValue("@Param", sqlDbType).Value = Param;
                con.Open();
                cmd.ExecuteNonQuery();

                **********
                *** OR ***
                **********

                cmd.CommandType = CommandType.Text;
                cmd.Parameters.AddWithValue("@Param", sqlDbType).Value = Param;
                using (SqlDataAdapter da = new SqlDataAdapter(cmd))
                {
                    da.Fill(dtInfo );
                }
            }
        }

---

So, if I’m understanding the provided information, this is my best route?

        using (SqlConnection con = db.con(user.Authority))
        {
            string command = "SELECT [TBL_EMPLOYEE].[ACTIVE_DIRECTORY] FROM [TBL_EMPLOYEE];";
            using (SqlCommand cmd = new SqlCommand(command, con))
            {
                con.Open();
                using (SqlDataReader reader = cmd.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        MessageBox.Show(reader["ACTIVE_DIRECTORY"].ToString());
                    }
                }
            }

And one last thing… This should prevent the need for

cmd.Dispose();
etc...

Answer 1

I would not use the SqlDataAdapter version. The version that uses the SqlCommand object and the SqlDataReader will perform better, and allows more insight into the actual data being returned.

// Assumes the following sql:
//   SELECT foo, bar FROM baz

// error checking left out for simplicity
var list = new List<SomeClass>();
using(var reader = cmd.ExecuteReader()) {
   while(reader.Read()) {
      list.Add(new SomeClass {
         // NOTE: you can see the columns that the c# is referencing
         //       and compare them to the sql statement being executed
         Foo = (string)reader["foo"],
         Bar = (string)reader["bar"]
      });
   }
}

Later as your level of experiance increases you will be able to use other features of the SqlCommand and SqlDataReader classes in order to ensure that the code executes as quickly as possible. If you start using the SqlDataAdapter route, you will eventually have to relearn how to do the exact same things you have already been doing because the SqlCommand and SqlDataReader have operations that do not exist elsewhere in .NET.