Hello everyone, I have a task that several other tasks depend on in my prefect flow. In airflow I could do something like

F1 >> [f2, f3, f4, f5, f6]

What's the best way to set these dependencies in Prefect. I notice that set_downstream doesn't accept a list of tasks. Is there any efficient way to do this in Prefect? Also does the new Prefect UI mean I don't need docker to run it? Thanks

Hi @Qwame - you can set upstream or downstream tasks by passing an array to the

upstream_tasks

or

downstream_tasks

task constructor, or using the

set_dependencies

method like such:

from prefect import Flow, task
 
@task
def F1():
    print("F1")
    return

@task
def f2():
    print("f2")

@task
def f3():
    print("f3")

with Flow("F Flow") as flow:
    f1 = F1()

    f2(upstream_tasks=[f1])
    f3(upstream_tasks=[f1])

or:

from prefect import task, Flow

@task
def F1():
    print("F1")

@task
def f2():
    print("f2")

@task
def f3():
    print("f3")
    
with Flow("F Flow") as flow:
    F1.set_dependencies(downstream_tasks=[f2, f3])

Thank you very much @nicholas

Happy to help!

It is interesting how the second example is set up

Both are valid; one builds the dependency graph based on the reference to the task call (which is your example), and the other dependency graph is built based on Prefect's knowledge of your intention to call a task (understood from your passing a reference to the task itself)

I have tried set_dependencies using both the functional and imperative API and I must admit that I'm very happy with Prefect. I haven't been successful at using the UI without docker. I am unable to use docker that's why I have to install and run each service individually. I cloned the repo, and followed the instructions to build the Prefect development server. The UI showed in the browser at port 8080 but I couldn't connect my flows to the UI. I used flow.register() but it didn't work. The error was related to connection to the port. Any idea what I might be missing?

@Qwame did you ever figure out what was wrong? I think I am having a similar connection issue

@Archie35 nope I could not figure out what was wrong.