duplicate entry message

[Lauren B]

I am attempting to code my form so that if a user enters a Customer ID
already in use, they will get a message box that tells them immediately
after leaving the corresponding text box. (as opposed to getting an error
message when attempting to save the entry after fully completing the form).
I am attempting to use the following code in the before update property of
the text box ("TxtBxCustomer_ID"):

DLookUp ("Customer_ID" , "Table1" , Customer_ID = " ' " &
Me.TxtBxCustomer_ID & " ' " then
Msgbox "Duplicate entry. Please make a new selection."

This code is not working. I am not getting an error message, it just simply
is doing nothing. How can I change this code to work properly.

Thank you for any assistance.

LB

 

[Guest]

If not IsNull(DLookUp ("Customer_ID" , "Table1" , Customer_ID = " ' " _
& Me.TxtBxCustomer_ID & " ' " ) then
Msgbox "Duplicate entry. Please make a new selection."
Cancel = True
End If