“already an open DataReader” exception with nested SqlDataReader in ASP.NET

Question

I wanted to use nested SqlDataReader in the code below but I couldn't make it.I get "System.InvalidOperationException: There is already an open DataReader associated with this Command which must be closed first" with the code. Any Suggestions

            c = "select user_Reps.rep_key,Officers.Officer_Name from user_Reps left join Officers on user_Reps.rep_key = Officers.Officer_code where [user_key]="+userCode;
            if (c == null)
                c = sr.ReadToEnd();
            try
            {

                SqlCommand cmd = new SqlCommand(c, cn);
                cn.Open();
                SqlDataReader rdr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                List<Dictionary<string, object>> list = new List<Dictionary<string, object>>();
                SqlDataReader rdr2;
                while (rdr.Read())
                {
                    string c2 = "select Active_Clients.Clients_code,Active_Clients.Clients_Name,Active_Clients.Geo_code  from Active_Clients where Active_Clients.[Officer_code] =" + rdr.GetValue(0) + " order by Clients_Name";
                    SqlCommand cmd2 = new SqlCommand(c2, cn);

                    rdr2 = cmd2.ExecuteReader(CommandBehavior.CloseConnection);


                    Dictionary<string, object> d = new Dictionary<string, object>(rdr.FieldCount+rdr2.FieldCount);
                    while (rdr2.Read())
                    {
                        int i = 0;
                        for (; i < rdr.FieldCount; i++)
                        {
                            d[rdr.GetName(i)] = rdr.GetValue(i);
                        }

                        for (; i < rdr2.FieldCount; i++)
                        {
                            d[rdr2.GetName(i)] = rdr2.GetValue(i);
                        }

                        list.Add(d);
                    }




                    rdr2.Close();

                    //list.Add(d);
                }
                JavaScriptSerializer j = new JavaScriptSerializer();
                Response.Write(j.Serialize(list.ToArray()));

            }

Answer 1

The error message is a bit misleading. Unless you have MultipleActiveResultSets=True in your connection string, you can have only one active result set per connection. This is still the case, if every reader hat it's own separate SqlCommand object.

Answer 2

You cannot have two open DataReaders on the same connection at the same time.

A common solutions to this problem would be to load the contents of the first DataReader into a DataTable or List<> before opening the next DataReader. You could also open a new connection for the nested query.

Edit Or, as @Mithrandir mentioned, you can use the MultipleActiveResultSets=true on the connection string.

Answer 3

Assuming it's on a sql server version 2005 or higher, enabling Multiple active resultsets (MARS) should do the trick I think. http://msdn.microsoft.com/en-us/library/h32h3abf%28v=vs.80%29.aspx . If MARS is not an option, a different connection should be opened for the second command.