How to wait until data in signal is valid

Community Support
1

I need to validate the data in activity before proceeding further, the question is how I can achieve that.
By re-running workflow if data is not valid? Can I do it inside the signal definition? Or is there a better way?

    @workflow.run
    async def run(self, uuid: str) -> str:
        while True:
            await workflow.wait_condition(lambda: not (self._data is None), timeout=45)
            valid = await workflow.execute_activity(
                validate_data,
                self._data,
                start_to_close_timeout=timedelta(minutes=2)
            )
            if valid:
                #we are good
            else
                #signal that data is wrong, wait for new data
2

Yes, you can do it in the signal definition or, as is often clearer, what you have there where you wait for the an attribute like _data to be set by a signal handler. It’s up to you on how to handle invalid data. If you want to fail the workflow, you can raise temporalio.exceptions.ApplicationError("some error").

3

So I can do something like this:

    @workflow.signal(name="FORM_SUBMITED")
    async def form_submitted(self, res: str) -> None:
          valid = await workflow.execute_activity(
                validate_data,
                self._data,
                start_to_close_timeout=timedelta(minutes=2)
         )
         if valid:
            self._data = res
         else:
            # do something else

And it should work fine?

4

Yes, however it can be confusing for readers if you put too much async logic inside of signal handlers. It separates the logic quite a bit so if, say, someone comes later and wants to add a try/except to catch all workflow errors and do something, they will miss errors that could occur here (errors out of signal handlers suspend/fail workflows just like if they were thrown out of run).

Often people will do something like you had before with wait_condition and set an attribute, or use an instance attribute of asyncio.Queue to push signals to and get them on the main run method. This keeps logic close together.