Please help!! How to increment the value of rows in vb.net

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I want the value of row(0) to be start from 100000 if the table is null, and that's why I want to check the row(0) and if the value is null, textbox14 should be filled by 100000 so that I can save it to the table. Here's what I've done so far for this task.

VB

Private Sub autoincrement()
        getconnect()
        If con.State = ConnectionState.Closed Then
            con.Open()
        End If
        ds.Tables.Add(dt)
        Dim reg_id As Double
        reg_id = ds.Tables(0).Compute("Max(registrationID)", Nothing)
        If reg_id = vbNull Then
            TextBox14.Text = "100000"
        Else
            TextBox14.Text = reg_id + 1
        End If
    End Sub

When I start debugging, I see this message on the screen--
Conversion from type 'DBNull' to type 'Double' is not valid.

Posted 27-Jan-13 21:55pm

suhan 2012

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Comments

Jameel VM 28-Jan-13 4:24am

After getting the Datatable results. what you want to do?

3 solutions

Solution 1

Before assigning value to reg_id, check if the value in the table is null or not. Note that you need to check for DbNull.Value and not for nothing.

Posted 27-Jan-13 22:04pm

dan!sh

Solution 4

VB

Private Sub autoincrement()
        getconnect()
        If con.State = ConnectionState.Closed Then
            con.Open()
        End If
        ds.Tables.Add(dt)
        Dim reg_id As Double
        reg_id = ds.Tables(0).Compute("Max(registrationID)", Nothing)
'------------- Take note here-------------------------------
         'Get the max row index
         Dim lastRowIndex As Integer = ds.Tables(0).Rows.Count - 1 
         If lastRowIndex < 0 Then 
            ' zero rows
              TextBox14.Text = "100000"
          Else
              Dim IsNum As BooleanIsNum = Double.TryParse(ds.Tables(0).Row(lastRowIndex) & _("registrationID").ToString ,regid)
           TextBox14.Text = reg_id + 1

          End If     
'-----------------------------------------------------------
       
            
        
    End Sub

Posted 27-Jan-13 23:41pm

codejet

Comments

suhan 2012 28-Jan-13 10:34am

Having some problem with BooleanIsNum..

codejet 29-Jan-13 2:25am

Dim IsNum As Boolean

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Jameel VM · Accepted Answer · 2013-01-27T22:30:00

Solution 2

Please change your code like below

VB

Private Sub autoincrement()
    getconnect()
    If con.State = ConnectionState.Closed Then
        con.Open()
    End If
    ds.Tables.Add(dt)
    If ds.Tables.Rows.Count <> 0 Then
        Dim reg_id As Double = 0
        reg_id = ds.Tables(0).Compute("Max(registrationID)", Nothing)
        TextBox14.Text = reg_id + 1
    Else
        TextBox14.Text = "100000"
    End If


End Sub

Posted 27-Jan-13 22:30pm

Jameel VM

Comments

suhan 2012 28-Jan-13 10:30am

Working fine. Thanks.

Jameel VM 29-Jan-13 1:56am

Please put a condition before iterating the rows.
like if(dt.rows.count!=0)
{
//loop here
}

suhan 2012 29-Jan-13 2:03am

Sir, Sorry for that, actually it is my login form's code.

Actually I wanted to tell you that your code is working fine when I open that form as startup form. But when I try to open that form after logging in I'm getting the same error. "Conversion from type 'DBNull' to type 'Double' is not valid." I think there is a conflict between the login form and user form. Can you please tell me how to solve this?

Jameel VM 29-Jan-13 2:05am

Please put the code that you got exception

suhan 2012 29-Jan-13 2:12am

Dim reg_id As Double = 0
reg_id = ds.Tables(0).Compute("Max(registrationID)", Nothing)

suhan 2012 29-Jan-13 2:16am

Actually I'm getting the exception if the table is completely blank and I open that user form after log in form. But when I open it as startup form, it works.

Jameel VM 29-Jan-13 2:19am

Please put the condition by checking whether collection is empty or not wherever you have write such codes.You can't done any operation(like compute) on that table(dataTable) when the collection is empty

suhan 2012 29-Jan-13 2:24am

ok, thanks