Duplicate detection in commcare

Users
1

Hi,

I’m using a registration form (Prelevement) where a have a ID field called (Participant_id). I want to detect a duplicate number for this field where the mobile worker submit a form.

I use this validation condition code:

count(instance('casedb')/casedb/case[@case_type = 'Prelevement'][Participant_id = Participant_id]) = 0

But it’s not working. Please help!

2

the second participant id should be referencing something in your form