If statment Help - Simon

On my form i have a button that when it gets pressed it adds data to
the subform. the code works fine

I just want a if statment that will stop the code working if data
alredy existes in the subform.

If data exists i want a error message, if ther is no data let the code
run


Im not sure how to code it for it to see if there is data in the
subform


Any help will be great


Simon

If statment Help - SJ

Hopefully you've got a KEY field in the subform,  an identifying field,  a
primary key???

if you have then use code like

if isnull(Subform.Form.Primarykeyfield) then

you have no records

the Subform and Primarykeyfield   need to be changed to be your apps names.
eg,    InvoiceLines.Form.InvoiceNo