Qty Control in C#

Question

pstrjds, From the code you have provided I am trying to implement that code and the msdn link you provided couple of days ago. I am not sure how to put it together but I am see

Answer 1

After reading your question again, I am more convinced that the comment I posted is actually the problem. You said in your question that your quantity is not going down. If you look at the return value from the line:

cmd.ExecuteNonQuery();

in your else statement I believe you will get a value of 0. This indicates that no records where updated. I believe the problem is exactly related to your query. If you connect to your database with a utility such as LINQPad or the Sql Management studio and run the query you have listed in your code I think you will find it is not updating anything. I highly suspect that your inventory is not being stored in a table called tblContacts. Which is why you can't select a quantity from it nor update a quantity in it.

Edit: Meant to mention this initially and then got sidetracked and forgot to add it. I would put your SqlCommand in a using statement. The SqlCommand object is disposable and so it is good practice to place disposable objects in a using statement or in some sort of try/finally pattern where they can be cleaned up.

Additional edit - restructuring your code:

    cs.Open();
    int remainingStock = 0;
    string Query = "SELECT QTY from tblInventory WHERE ID=19";
    using(SqlCommand cmd = new SqlCommand(Query, cs))
    {
        var result = cmd.ExecuteScaler();
        if (result != null)
        {
            string str = result.ToString();
            if (!string.isNullOrWhiteSpace(str))
            {
                // NOTE: It would probably be safer to use int.TryParse here
                remainingStock = Convert.ToInt32(cmd);
            }

            if (remainingStock == 0)
            {
                lbqty.Text = "Not enough stocks.";
            }
            else
            {
                cmd.CommandText = "UPDATE tblInventory SET QTY = QTY-1 WHERE ID=19";
                int rowsUpdated = cmd.ExecuteNonQuery();
                remainingStock--;

                if (remainingStock == 1)
                {
                    lbqty.Text = "Re-order. Remaining stocks: 1";
                }
                else
                {
                    string remaining = "Remaining stocks: " + remainingCount.ToString();
                    txtQty.Text = remaining;
                    lbqty.Text = remaining;
                }
            }
        }
        else
            lbqty.Text = "No stock for contact";
        }

        dgUpdate();
    }
    cs.Close();