Validate Duplication of ID in Database

[manutd4life]

Hello, I have a program connecting with a database..
so when add record in it, i want to validate for the duplication of ID in database..

here's my code for add button:

Private Sub cmdAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdAdd.Click
        dSet.Tables(0).PrimaryKey = New DataColumn() {dSet.Tables(0).Columns("WatchID")} 'The table primary key is the WatchId
        Dim row As DataRow
        row = dSet.Tables(0).Rows.Find(txtWatchId.Text) 'the textbox id will be searched 
        If txtWatchId.Text = row("WatchID") Then 'validating duplicating id
            MsgBox("Watch ID already exist") 'messagebox to notify the user
            'here validating if the textboxes is empty
            'and a message will be displayed to notify the user
        ElseIf txtWatchId.Text = "" Then
            MsgBox("Watch ID is empty")
        ElseIf txtWatchBrand.Text = "" Then
            MsgBox("Watch Brand is empty")
        ElseIf txtWatchModel.Text = "" Then
            MsgBox("watch model is empty")
        ElseIf txtManufacturer.Text = "" Then
            MsgBox("Manufacturer is empty")
        ElseIf txtCountryOfOrigin.Text = "" Then
            MsgBox("Country of origin is empty")
        ElseIf txtDescription.Text = "" Then
            MsgBox("Description is empty")
        ElseIf cmbType.Text = "" Then
            MsgBox("Please choose a type")
        ElseIf txtPrice.Text = "" Then
            MsgBox("Price is empty")
        ElseIf Not IsNumeric(txtPrice.Text) Then 'validating if the price is not numeric
            MsgBox("Price is not numeric") 'message will be displayed
        ElseIf txtPriceInclVat.Text = "" Then
            MsgBox("Please calculate VAT")
        ElseIf Not IsNumeric(txtPriceInclVat.Text) Then 'validating if Price incl vat is not numeric
            MsgBox("Price plus VAT is not numeric") ' a message box is displayed to inform the user
        Else
            'After passing througth all these validation, the record is addes in the database
            Dim com As New OleDbCommand
            com.Connection = con
            'inserting the record in the watches table
            com.CommandText = "insert into Watches values('" & txtWatchId.Text & "','" & txtWatchBrand.Text & "','" & _
                                txtWatchModel.Text & "','" & txtManufacturer.Text & "','" & txtCountryOfOrigin.Text & "','" & _
                                cmbType.Text & "','" & txtDescription.Text & "'," & txtPrice.Text & "," & txtPriceInclVat.Text & ")"

            com.ExecuteNonQuery()
            MsgBox("Record Inserted") 'message box is displayed to inform the user that the record has been inserted in the database
            cmdUpdate.Enabled = True 'update button enabled
            cmdDelete.Enabled = True 'delete button enabled
            cmdAdd.Enabled = False 'add button enabled
            cmdfirst.Enabled = True 'first button enabled
            cmdPrevious.Enabled = True 'previous button enabled
            cmbNext.Enabled = True 'next button enabled
            cmdLast.Enabled = True 'last button enabled
            Call populate() 'populate procedure is called
            Call populate_fill() 'populate_fill is called
            Call fill_combo() 'fill_combo is called
        End If
    End Sub

here's the code for validation:

dSet.Tables(0).PrimaryKey = New DataColumn() {dSet.Tables(0).Columns("WatchID")} 'The table primary key is the WatchId
        Dim row As DataRow
        row = dSet.Tables(0).Rows.Find(txtWatchId.Text) 'the textbox id will be searched 
        If txtWatchId.Text = row("WatchID") Then 'validating duplicating id
            MsgBox("Watch ID already exist") 'messagebox to notify the user

so when i click on add, it says..NullReferenceException was unhandled

see screenshot below

thanks

[Unhnd_Exception]

The DataRowCollection returns null if nothing is found.

If its nothing then it wasn't found.

Dim row As DataRow
row = dSet.Tables(0).Rows.Find(txtWatchId.Text) 'the textbox id will be searched 
If row isnot nothing Then 'validating duplicating id
    MsgBox("Watch ID already exist") 'messagebox to notify the user

[manutd4life]

The DataRowCollection returns null if nothing is found.

If its nothing then it wasn't found.

Dim row As DataRow
row = dSet.Tables(0).Rows.Find(txtWatchId.Text) 'the textbox id will be searched 
If row isnot nothing Then 'validating duplicating id
    MsgBox("Watch ID already exist") 'messagebox to notify the user

thanks.. works great
thank you very much

[Netcode]

you can simply set the ID column as a primary key in the DBMS