Hey all, New to the community and Prefect in general, but a bit in love with it already 🙂 I have a basic architectural question, and I hope this is a good place to ask it - otherwise, please let me know! In a nutshell, I am looking to

map

case

. More in detail, I am converting into Prefect an existing process currently run locally through a simple CLI, to fetch and handle datasets from a remote server. One of the first things in this process is checking the dataset version, using 

check_version(id)

 which returns a 

bool

. In the CLI this is then used in a simple logical block to determine how to continue. In the CLI a list of ids is handed and looped over, making that check for each element in the list (sequentially). I want to convert this into Prefect and take advantage of the parallelisation opportunities. Therefore, I thought that 

case

 and 

map

 would work great here, something like this (which is not possible):

ids = [id1, id2, id3]
with Flow('Check version') as flow:
    with case (check_version.map(id=ids), True):
        val1 = action_if_true()
    with case (check_version.map(id=ids), False):
        val2 = action_if_false()

The issue here being that the output from 

check_version(id)

 is mapped, and is therefore a list of bools - 

[True, True, False]

, which cannot be compared against a 

bool

. I found no option to map `case`. I did however see the option to map `switch`, and I could imagine using that if I have to, but since it must take strings as input (it uses a

dict

to get the different scenarios) it would require a conversion or changing the original functions in the CLI, which I would rather not do. This is a pretty simple thing, and I imagine someone else has solved this before, but could not locate anything in the docs or other places. Or perhaps I am thinking about this in the wrong way. Any input is welcome, thanks!

Hey @Amit Gal would

apply_map

solve your use case? (bottom of the page here https://docs.prefect.io/api/latest/utilities/tasks.html#functions)

Indeed, I believe so, thanks for the prompt assist!

I believe so, yes

Great, thanks. That's not ideal, but not a big issue. And then all following tasks would be nested under the

do_if_v4

function? As in:

def do_if_v4(id):
    with case (check_version_task(id), True):
        val1 = get_data_task()
        val2 = do_something_task()
        val3 = do_another_thing_task()
        .
        .
        .
        val4 = upload_somewher_task
    with case (check_version_task(id), False):
        same_things_here
        ...
        ...
        ...

with Flow('conditional flow') as flow:
    apply_map(do_if_v4, ids)

I'm asking because that seems to be breaking from the regular way of writing each task as a line in the flow (which I really like)

Yeah

Got it, thanks for your help!