[RESOLVED] Conversion from type 'DBNull' to type 'String' is not valid

[tqmd1]

Dear Experts
I use following codes to retrieve data from table, but get error

Conversion from type 'DBNull' to type 'String' is not valid.

str = "Select * from gpass where vou_no= " & Val(Me.txtGat.Text) & " And Date =   '" & Me.txtDat.Text & "'"
        dt = GetTable(str)

        If (dt.Rows.Count > 0) Then


            DataGridView1.Rows.Clear()

            For i = 0 To dt.Rows.Count - 1

                Me.DataGridView1.Rows.Add()
                Me.DataGridView1.Rows(i).Cells(1).Value = IIf(IsDBNull(dt.Rows(i)("tittle")), " ", Trim(dt.Rows(i)("tittle")))
            Next
        End If
End If

Tittle column of gpass is as

Column------datatype
Tittle--------char(100)

And data in column is as
Null
Null
Null


Please help

[jmcilhinney]

In VB 2008 you should be using If, not IIf. One of the problems with IIf is that both possible values get evaluated, so you're trying to Trim a DBNull value even if you don't intend to use it. The new If operator short-circuits, meaning that only the expression for the value that will be returned is evaluated.

That said, why do you need to any of that? Why can't you just do this:

Me.DataGridView1.Rows(i).Cells(1).Value = dt.Rows(i)("tittle")

A null value will be displayed in exactly the same way as an empty string in that case, so there's no need to check. If the problem is that you want to Trim a non-empty string then you can do this:

Me.DataGridView1.Rows(i).Cells(1).Value = dt.Rows(i)("tittle").ToString().Trim()

By the way, assuming it's English, there's no such word as "tittle". That should probably be "title".

Finally, you should also be using parameters to insert values into your SQL code rather than string concatenation. Follow the Database FAQ link in my signature for more information on that.

[nbrege]

FYI... http://en.wikipedia.org/wiki/Tittle

[jmcilhinney]

FYI... http://en.wikipedia.org/wiki/Tittle

Hmmm... Never say never I guess. Given the context though, I'm going with "title" on this one.