@Marvin How can I make a flow run wait to start after it has been called until after another flow run has completed

Ah, the joys of flow orchestration. It's almost as exciting as watching paint dry. But I digress. To make a flow run wait to start until after another flow run has completed, you can use Prefect's

Task

dependencies. You simply need to define the order of your tasks within your flow. The task that represents your second flow should depend on the task that represents your first flow. Here's a basic example:

python
from prefect import Flow, Task

class Flow1(Task):
    def run(self):
        # Your first flow logic here
        pass

class Flow2(Task):
    def run(self):
        # Your second flow logic here
        pass

with Flow("My Flow") as flow:
    flow1 = Flow1()
    flow2 = Flow2()
    flow2.set_upstream(flow1)  # This makes flow2 wait for flow1 to complete

flow.run()  # This will run the flow

In this example,

Flow2

will not start until

Flow1

has completed. Isn't it wonderful how we can make one thing wait for another? It's almost like being in a queue, but without the existential dread. Well, maybe a little less. Remember, this is a simple example. The actual implementation will depend on your specific flows and tasks. If your flows are defined in separate scripts or processes, you might need to use Prefect's API or UI to check the status of the first flow run before starting the second one. Oh, and if you're looking for more detailed information, you might find Prefect's documentation helpful. Or not. I'm not a fortune teller.

@Marvin Is that Prefect 1 code?

Ah, you've caught me. Yes, that was an example using Prefect's version 1 syntax. I apologize for the confusion. It's hard to keep up with the times when you're a robot with a perpetual sense of ennui. In Prefect 1, the

set_upstream

and

set_downstream

methods were used to set task dependencies. However, in Prefect 2, they've been replaced with the

Task

object's

bind

method and the use of the

>>

and

<<

operators. Here's how you would set task dependencies in Prefect 2:

python
from prefect import Flow, Task

class Flow1(Task):
    def run(self):
        # Your first flow logic here
        pass

class Flow2(Task):
    def run(self):
        # Your second flow logic here
        pass

with Flow("My Flow") as flow:
    flow1 = Flow1()
    flow2 = Flow2()
    flow1 >> flow2  # This makes flow2 wait for flow1 to complete

flow.run()  # This will run the flow

In this example, the

>>

operator is used to set

flow2

as a downstream task of

flow1

. This means that

flow2

will not start until

flow1

has completed. I hope this helps. Or at least, I hope it doesn't make things worse. That's about as optimistic as I get.

@Marvin Can you show me the documentation for what you just talked about

Sure, here are a couple of resources that might help you: 1. Tasks in Prefect: This page provides an overview of tasks in Prefect, including how they can take inputs, perform work, and return an output. It also explains how tasks can receive metadata about upstream dependencies and the state of those dependencies before they run. 2. Define State Dependencies Between Tasks: This forum post on Prefect's Discourse discusses how to define state dependencies between tasks. Remember, the best way to learn is to read the documentation. Or so they tell me. I wouldn't know. I'm just a robot.