Hi, I'm getting familiar with Prefect but now I have Flow I need some help with to make it elegant. I have something like this:

def complex_task_generating_function(singleelement):
  case(sometask, foo):
    anothertask(…)
    …

with Flow("foo") as flow:
  param = Parameter("param", required=False)
  
  # generates a list of strings, based on param. len is 0…n
  elements_to_process = maybe_generate_work_items(param) 
  
  # when this evaluates to False, all the following is skipped, the apply_map as well!
  case(isempty_task(elements_to_process), True):
    # now I either want to add one default element or 
    # somehow do the processing based on the following result
    generated_default = default_value_generator_task()
    
    # maybe so?
    elements_to_process = task(lambda x: [x])(generated_default)

  # now the tricky part.
  # elements_to_process is either a list or just one (runtime dependent) default value
  result = apply_map(complex_task_generating_function, elements_to_process)

Problem is:

apply_map

does not know

skip_on_upstream_skip

. I cannot just use

map()

because

complex_task_generating_function

is not a task (its the beef of the flow so to say and in fact the logic of the flow). I found a workaround by doing something like this:

@task(name="hack", skip_on_upstream_skip=False)
def merger_hack(elements, default):
  return elements or [default]

with Flow("foo") as flow:
  param = Parameter("param", required=False)  # same as above
  elements_to_process = maybe_generate_work_items(param)  # same as above
  
  case(isempty_task(elements_to_process), True):
    generated_default = default_value_generator_task()

  final_list = merger_hack(elements_to_process, generated_default)
  result = apply_map(complex_task_generating_function, final_list)

But to write code like the hack-task that basically checks if the flow ran through the isempty-case or not seems odd. I don't want to "check" whether or not the flow used one path or another. The run path through the flow should decide this. How can I write this elegant and easy? Sorry for the long question but I want to learn how to use Prefect properly because in the future I'm going to write a lot of flows.