How do I go about using DLookup in a validation rule of a text box on a form in access

Question

Hello

I am trying to use DLookup for a ValidationRule for a TextBox on a form in Access.

As per an example found on MSDN I used

dlookup("ABKUERZUNG", "tblABKUERZUNG", "ABKUERZUNG=[Forms]![frmMutBetriebspunkt]![BP_ABKUERZUNG]") is null

Which does not work: The expression you entered contains invalid syntax.

Now, if someone knew what and where exactly this invalid syntax is, I'd be grateful.

Thanks Rene

edit: corrected wrong ' to " (which was not the cause of the problem)

Answer 1

EDITED

For Code:

If IsNull(dlookup( _
"ABKUERZUNG", "tblABKUERZUNG", _
"ABKUERZUNG=[Forms]![frmMutBetriebspunkt]![BP_ABKUERZUNG]")) Then

For a Validation Rule:

dlookup("ABKUERZUNG", "tblABKUERZUNG", "ABKUERZUNG=[Forms]![frmMutBetriebspunkt]![BP_ABKUERZUNG]")=Null

Answer 2

You may want isolate the string you are creating for your filter, so you could check in the immediate window if the value is what you expect.

dim sFilter as String

sFilter = "ABKUERZUNG='" & [Forms]![frmMutBetriebspunkt]![BP_ABKUERZUNG] & "'"

dlookup("ABKUERZUNG", "tblABKUERZUNG", sFilter) is null

Answer 3

If you use a function in code, the parameter separator is the comma(,), but in the GUI-editor it is the semicolon (;). This could be your syntax error.

So try:

=Dlookup("field";"table";"where")