hi everybody, i saw this in the prefect document

from prefect import Task, Flow
from prefect.tasks.prefect import StartFlowRun


class ExtractSomeData(Task)
    def run(self):
        return {"param-key": "some-random-piece-of-data"}

extract_some_data = ExtractSomeData(name="extract_some_data")

# assumes you have registered a flow named "exampled" in a project named "examples"
flow_run = StartFlowRun(flow_name="example", project_name="examples")

with Flow("parent-flow") as flow:
    flow_run.set_upstream(extract_some_data, key="parameters")

but i am wondering what is the

parameters

? and whether the

param-key

from

ExtractSomeData

is passed into the

example flow

The

parameters

input for

StartFlowRun

accepts a dictionary, and passes each key-value pair as a parameter to the triggered flow. So this

StartFlowRun

call will trigger a flow run for the flow with name

example

. The flow run will have a single

Parameter

set up. Its name will be

"param-key"

, value will be

"some-random-piece-of-data"

. Its value can be accessed with the parameter task:

Parameter("param-key")

within the flow named

"example"

. In essence, this is analogous to setting inputs in the flow run page of the prefect UI.

Hi @Jeremy Tee! Emere is spot on here. I’ll add a final note that the

StartFlowRun

Task does not return data, it only kicks off the child Flow Run. If you need to send data back to the parent Flow, put that data in a known place, either by passing a parameter or using the Flow Run ID.

thank you all!