SQL Update with where clause with variables from VS2010 Winforms - vb.net

Question

I am trying to do an update query from a winform with two variables without using a dataset.
I assign both of my variable and then run the query but it keeps giving the error that zcomp is not a valid column name. Which of course is true but I tell it which column before I say = zcomp. Below is my code that is running the query.
Dim zamnt As Integer = WopartsDataGridView.Rows(e.RowIndex).Cells(e.ColumnIndex).Value
Dim zcomp As Integer = gridRow.Cells(0).Value
Dim con As New SqlConnection
Dim cmd As New SqlCommand
Try
con.ConnectionString = "Data Source=MNT-MGR-2\SQLEX;Initial Catalog=MT;Integrated Security=True"
con.Open()
cmd.Connection = con
cmd.CommandText = "UPDATE dbo.sparts SET [dbo.sparts.QtyonHand] = [dbo.sparts.QtyonHand] - zamnt WHERE [ComponentID] = zcomp"
cmd.ExecuteNonQuery()
Catch ex As Exception
MessageBox.Show("Error while updating record on table..." & ex.Message, "Update Records")
Finally
con.Close()
gridRow.Cells(4).Value = "Yes"
End Try
I have tried it several different ways. It works just fine if I take out the zamnt and zcomp and put the actual number values that are in the variables. Please help I've been searching all day for a way to use the variables with this update query.
Thanks,
Stacy

Answer 1

You are probably looking for how to use parameters in ADO.NET. For your example, it can look like this:
cmd.Parameters.Add("#zamnt", zamnt);
cmd.Parameters.Add("#zcomp", zcomp);
Put these two lines anywhere before ExecuteNonQuery.
Because parameters need a # prefix, you would also need to change your query to say #zamnt instead of just zamnt, and same for zcomp:
cmd.CommandText = "UPDATE dbo.sparts SET [dbo.sparts.QtyonHand] = [dbo.sparts.QtyonHand] - #zamnt WHERE [ComponentID] = #zcomp"

Answer 2

In addition to using parameters, the "Using" statement closes the connection and disposes resources:
Dim zamnt As Integer = WopartsDataGridView.Rows(e.RowIndex).Cells(e.ColumnIndex).Value
Dim zcomp As Integer = gridRow.Cells(0).Value
Try
Using con As New SqlConnection("Data Source=MNT-MGR-2\SQLEX;Initial Catalog=MT;Integrated Security=True")
con.Open()
Using cmd As New SqlCommand
cmd.CommandText = "UPDATE dbo.sparts SET [dbo.sparts.QtyonHand] = [dbo.sparts.QtyonHand] - #zamnt WHERE [ComponentID] = #zcomp"
cmd.Parameters.AddWithValue("#zamt", zamnt)
cmd.Parameters.AddWithValue("#zcomp", zcomp)
cmd.ExecuteNonQuery()
End Using
End Using
Catch ex As Exception
MessageBox.Show("Error while updating record on table..." & ex.Message, "Update Records")
Finally
con.Close()
gridRow.Cells(4).Value = "Yes"
End Try

Answer 3

have u tried this?
Dim zamnt As Integer = WopartsDataGridView.Rows(e.RowIndex).Cells(e.ColumnIndex).Value
Dim zcomp As Integer = gridRow.Cells(0).Value
Dim con As New SqlConnection
Dim cmd As New SqlCommand
Try
con.ConnectionString = "Data Source=MNT-MGR-2\SQLEX;Initial Catalog=MT;Integrated Security=True"
con.Open()
cmd.Connection = con
cmd.CommandText = "UPDATE dbo.sparts SET [dbo.sparts.QtyonHand] = [dbo.sparts.QtyonHand] -" + zamnt + " WHERE [ComponentID] =" + zcomp
cmd.ExecuteNonQuery()
Catch ex As Exception
MessageBox.Show("Error while updating record on table..." & ex.Message, "Update Records")
Finally
con.Close()
gridRow.Cells(4).Value = "Yes"
End Try