select as sql and use in asp.net - asp.net

Question

i want select from my sql and create a session from one table field
string strquery = "select * from Registration where username=#username ";
SqlConnection connection2 = DBConnection.getConnection();
connection2.Open();
SqlCommand cmd2 = new SqlCommand();
cmd2.Connection = connection;
cmd2.CommandText = strquery;
cmd2.Parameters.Add("#username", txt1_username.Text);
SqlDataReader nwReader = cmd2.ExecuteReader();
string cus = "";
if (nwReader.Read())
{
cus = nwReader["customer_id"].ToString();
}
nwReader.Close();
connection.Close();
Session["customer_id_se"] = cus.ToString();
Response.Redirect("Wedding.aspx");
my problem is: i can't use that field and use in session

Answer 1

You are doing few mistakes, let me point them first(obviously it will solve the issue too).
As i mentioned in the comment, "you are creating connection2 and
opening connection using connection.Open(); it should be either
connection2.Open(); or remove connection2 from the block.
The .Parameters.Add() method expect SqlDbType specify them and add its value using the following statement.
cmd2.Parameters.Add("#username",SqlDbType.VarChar).Value = txt1_username.Text;
There may be situations where nwReader will not having any rows(query returns no result). Accessing value from it in such situation will give you exception as "Invalid attempt to read when no data is present", So you need to check for existence of data in the Reader before accessing it.
That is you should use like the following:
SqlDataReader nwReader = cmd2.ExecuteReader();
string customerId = String.Empty;
if (nwReader.HasRows)
{
customerId = nwReader["customer_id"].ToString();
}
4. customerId is already a string so you need not to convert it again using .ToString() before assigning to the session. So the complete scenario can be coded as like the following:
string strquery = "select * from Registration where username=#username";
SqlConnection connection = DBConnection.getConnection();
connection.Open();
SqlCommand cmd2 = new SqlCommand();
cmd2.Connection = connection;
cmd2.CommandText = strquery;
cmd2.Parameters.Add("#username", SqlDbType.VarChar).Value = txt1_username.Text;
SqlDataReader nwReader = cmd2.ExecuteReader();
string customerID = "";
if (nwReader.HasRows)
{
customerID = nwReader["customer_id"].ToString();
}
nwReader.Close();
connection.Close();
Session["customer_id_se"] = customerID;
Note :-
If nwReader.HasRows is false means there is no such record for the
specific username, in this case customerID and hence
Session["customer_id_se"] will be blank.
Updates as per HansKesting's comment,
Select * will fetch the entire rows which satisfies the condition in the Where clause. If you requires only a single value and you are sure that the result will be either empty or a single value then you can use SELECT column_name from ... and in such situations use ExecuteScalar to get the value.