Exception Handling

What is Exception handling

• Exception Handling means apply the correct business logics when errors happen!

When to Handle Exception

• every HTTP Requests i.e. third party integration

How To Handle Exception

• How To Handle Exception (thanks to Sentry Django Project)
  • only catch specific exceptions when you have a meaningful way to handle them
  • Let exceptions bubble up unless you need to:
    • add context to the error
    • perform cleanup operations
    • covert one exception type to another with additional information
    • recover from expected error conditions

Reminder

• in general, one cannot revert a third party API call, because of possible side effects of the API call
• prefer the name Exception instead of Error, Exception is bounded in the exceptions raised by python code, Error can mean human errors and have much larger implication, makes it harder to think.
• it’s a business / BA decision when there is no perfect solution
  • confirmed with BA, on what should the error message be?
• use with transcation.atomic()
  • don’t use decorator @transaction.atomic to avoid future changes that introduces errors in error handling logics
• validate first, client facing logics last (e.g. sending emails)
• submission code / function must be idempotent to allow safe user retry or even auto retry
  • in Submission, avoid duplicate oneview and curo entities by using get_or_create?

Example: Curo

task = Task.objects.create(...) # or update some properties then task.save()
submit_entity_unhandled() # or submit_entity if errors doesn't matter?

Example: Third Party API Call

# if response data is needed
foo_id = third party POST or PATCH
raise_for_status()
save `foo_id` to local DB

• if third party call failed, not bad state, because there will be no local db changes.
• if save to local DB failed, bad state happened, maybe the solution is to verify first to avoid saving to local DB failed? because of the stable network or retry mechanism, unless this is DB constraint, save to local DB shouldn’t failed, so maybe verify can avoid the failure to local DB.