Skip to main content
Many of the parameters of automation actions can be defined with Jinja2 templates. These templates have access to objects related to the event that triggered your automation, including the deployment and flow run of that event (if applicable). Here we’ll explore an example illustrating how to access their parameters in an automation action. Let’s start with two flows, alpha and beta: 
from prefect import flow


@flow
def alpha(name: str, value: int):
    print(name, value)


@flow
def beta(name: str, value: int, another: float):
    print(name, value, another)
Once a run of alpha completes, we’ll automate running a flow of beta with the same parameters: 
from datetime import timedelta

from prefect.automations import (
    Automation,
    EventTrigger,
    Posture,
    ResourceSpecification,
    RunDeployment,
)

from .flows import alpha, beta

# Note: deploy these flows in the way you best see fit for your environment
alpha.deploy(
    name="alpha",
    work_pool_name="my-work-pool",
    image="prefecthq/prefect-client:3-latest",
)
beta_deployment_id = beta.deploy(
    name="beta",
    work_pool_name="my-work-pool",
    image="prefecthq/prefect-client:3-latest",
)

automation = Automation(
    name="Passing parameters",
    trigger=EventTrigger(
        # Here we're matching on every completion of the `alpha` flow
        expect={"prefect.flow-run.Completed"},
        match_related=ResourceSpecification(
            {
                "prefect.resource.role": "flow",
                "prefect.resource.name": "alpha"
            }
        ),
        # And we'll react to each event immediately and individually
        posture=Posture.Reactive,
        threshold=1,
        within=timedelta(0),
    ),
    actions=[
        RunDeployment(
            # We will be selecting a specific deployment (rather than attempting to
            # infer it from the event)
            source="selected",
            # The deployment we want to run is the `beta` deployment we created above
            deployment_id=beta_deployment_id,
            parameters={
                # For the "name" and "value" parameters, we tell Prefect we're using a
                # Jinja2 template by creating a nested dictionary with the special
                # `__prefect_kind` key set to "jinja".  Then we supply the `template`
                # value with any valid Jinja2 template.  This step may also be done
                # in the Prefect UI by selecting "Use Jinja input" for the parameters
                # you want to template.
                #
                # The "{{ flow_run }}" variable here is a special shortcut that gives us
                # access to the `FlowRun` object associated with this event.  There are
                # also variables like "{{ deployment }}", "{{ flow }}",
                # "{{ work_pool }}" and so on.
                #
                # In this case, the {{ flow_run }} represent the run of `alpha` that
                # emitted the `prefect.flow-run.Completed` event that triggered this
                # automation.
                "name": {
                    "template": "{{ flow_run.parameters['name'] }}",
                    "__prefect_kind": "jinja",
                },
                "value": {
                    "template": "{{ flow_run.parameters['value'] }}",
                    "__prefect_kind": "jinja",
                },
                # You can also just pass literal parameters
                "another": 1.2345,
            },
        )
    ],
).create()
If you are defining your automation in the Prefect web UI, you can switch the parameter input to support Jinja2 values: Use Jinja input for an action
⌘I