Controlling only one record by user

Hi,
I want as any user recorded can respond only once to the form.
I am using {user:id} to compare this id with the id recorded in the dbase.
I am using a read_data to know that (read_data34 in my e.g).
I think to create a variable, {var:read_data34.user_id}
But, how to use the var;, how to compare les two informations ? In a custom code, a loop? Ia am a lot lost...
Thank you
Bruno

Hi Bruno,
​
An Event Switcher action is probably the best way to manage this - you can have just one 'fail' event which shows an 'already submitted' message. Please see Page 30 of the Manual for more info on the Event Switcher.
​
Bob