Creating duplicate leads via API calls

Question

I have a rest API endpoint in Salesforce which accepts a payload from my application. On reception of the first request with a given email, it creates a lead. On subsequent requests, it finds the lead and updates the lead with extra information in the payload. My problem is that if a user quickly moves through the process (like have most of the fields filled and they just click the next button, it is a wizard-like interface), I have to call the API in quick succession. While the first call is creating the lead, the second call searches for a lead with a given email (which is not created yet) and starts the call to create a new lead. In the meantime, the first call has finished creating the lead as well. Now I have 2 leads instead of one :(

Is there a way on the Salesforce side I can handle this? Can't change the way requests land, sorry.

Answer 1

Use the FOR UPDATE SOQL keyword in Apex to require row locks for the leads you're querying. This ensures that the lead query matching by email will wait for any other in-flight records. This will ensure that you're not creating duplicates, even if the records are inserted simultaneously between two API calls.

Lead[] existingLead = [SELECT Email FROM Lead WHERE Email = :incomingEmail FOR UPDATE];