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This example shows how to use a trigger to schedule a run of downstream deployment when a run of an upstream deployment completes.

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Define an upstream and downstream deployment

event_driven_deployments.py
from prefect import flow, serve
from prefect.events import DeploymentEventTrigger


@flow(log_prints=True)
def upstream_flow():
    print("upstream flow")


@flow(log_prints=True)
def downstream_flow():
    print("downstream flow")


if __name__ == "__main__":
    upstream_deployment = upstream_flow.to_deployment(name="upstream_deployment")
    downstream_deployment = downstream_flow.to_deployment(
        name="downstream_deployment",
        triggers=[
            DeploymentEventTrigger(
                expect={"prefect.flow-run.Completed"},
                match_related={"prefect.resource.name": "upstream_deployment"},
            )
        ],
    )

    serve(upstream_deployment, downstream_deployment)

​
Test it out

First, start the serve process to listen for scheduled deployments runs: 
python event_driven_deployments.py
Now, run the upstream deployment and see the downstream deployment kick off after it completes: 
prefect deployment run upstream-flow/upstream_deployment
Check the event feedYou can inspect raw events in the event feed in the UI to see what related resources are available to match against.For example, the following prefect.flow-run.Completed event’s related resources include:
{
   "related": [
    {
      "prefect.resource.id": "prefect.flow.10e099ec-8358-4146-b188-be68027ee58f",
      "prefect.resource.role": "flow",
      "prefect.resource.name": "upstream-flow"
    },
    {
      "prefect.resource.id": "prefect.deployment.be777bbd-4b15-49f3-bc1f-4d109374cee2",
      "prefect.resource.role": "deployment",
      "prefect.resource.name": "upstream_deployment"
    },
    {
      "prefect.resource.id": "prefect-cloud.user.80546602-9f31-4396-ab4b-e873a5377feb",
      "prefect.resource.role": "creator",
      "prefect.resource.name": "stoat"
    }
  ]
}