davidnzhang opened a new pull request, #69171:
URL: https://github.com/apache/airflow/pull/69171
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# What
The scheduling dependencies endpoint is currently able to return an edge
with a `dag:` endpoint that is never materialised as a node. This appears to be
causing problems for the ELK renderer when creating the dependency graph in the
Assets UI.
This PR adds a loop to backfill any `dag:` nodes that are referenced by an
edge but are missing from the nodes set.
# Why
The scheduling view of the Assets dependency graph fails to render whenever
it contains a Dag referenced by another Dag (e.g. via `TriggerDagRunOperator`
or `ExternalTaskSensor`) and has no scheduling dependencies of its own.
The `get_scheduling_dependencies` function iterates over each Dag's
dependencies to build a list of nodes and edges. A Dag is only materialised as
a `dag:` node if it has at least one dependency of its own, but it is possible
for the same Dag to be an endpoint of an edge if it is referenced by another
Dag. This leaves a dangling edge whose endpoint is missing from the node set.
# Reproduction
Parent Dag
```python
from datetime import datetime
from airflow.providers.standard.operators.empty import EmptyOperator
from airflow.providers.standard.operators.trigger_dagrun import
TriggerDagRunOperator
from airflow.sdk import DAG, Asset
PARENT_ASSET = Asset(name="parent_dag_asset",
uri="s3://some-bucket/parent_dag_asset")
with DAG(dag_id="parent_dag", schedule=None, start_date=datetime(2021, 1,
1), catchup=False):
emit = EmptyOperator(task_id="emit", outlets=[PARENT_ASSET])
trigger = TriggerDagRunOperator(
task_id="trigger_child_dag",
trigger_dag_id="child_dag",
wait_for_completion=False,
)
emit >> trigger
```
Child Dag
```python
from datetime import datetime
from airflow.providers.standard.operators.empty import EmptyOperator
from airflow.sdk import DAG
with DAG(dag_id="child_dag", schedule=None, start_date=datetime(2021, 1, 1),
catchup=False):
EmptyOperator(task_id="some_task")
```
## Before
Scheduling view
<img width="440" height="442" alt="image"
src="https://github.com/user-attachments/assets/c3915e55-c21e-4a30-a6c7-f4af685168da";
/><br>
`/ui/dependencies?dependency_type=scheduling` Response
```json
{
"edges": [
{
"source_id": "dag:parent_dag",
"target_id": "asset:1"
},
{
"source_id": "dag:parent_dag",
"target_id": "trigger:parent_dag:child_dag:trigger_child_dag"
},
{
"source_id": "trigger:parent_dag:child_dag:trigger_child_dag",
"target_id": "dag:child_dag"
}
],
"nodes": [
{
"id": "dag:parent_dag",
"label": "parent_dag",
"type": "dag",
"team": null
},
{
"id": "asset:1",
"label": "parent_dag_asset",
"type": "asset",
"team": null
},
{
"id": "trigger:parent_dag:child_dag:trigger_child_dag",
"label": "trigger_child_dag",
"type": "trigger",
"team": null
}
]
}
```
## After
Scheduling view
<img width="1206" height="1212" alt="image"
src="https://github.com/user-attachments/assets/18bf8d41-f799-42cf-b130-04e2ed7c7211";
/><br>
`/ui/dependencies?dependency_type=scheduling` Response
```json
{
"edges": [
{
"source_id": "dag:parent_dag",
"target_id": "asset:1"
},
{
"source_id": "dag:parent_dag",
"target_id": "trigger:parent_dag:child_dag:trigger_child_dag"
},
{
"source_id": "trigger:parent_dag:child_dag:trigger_child_dag",
"target_id": "dag:child_dag"
}
],
"nodes": [
{
"id": "dag:parent_dag",
"label": "parent_dag",
"type": "dag",
"team": null
},
{
"id": "asset:1",
"label": "parent_dag_asset",
"type": "asset",
"team": null
},
{
"id": "trigger:parent_dag:child_dag:trigger_child_dag",
"label": "trigger_child_dag",
"type": "trigger",
"team": null
},
{
"id": "dag:child_dag",
"label": "child_dag",
"type": "dag",
"team": null
}
]
}
```
Note node set now correctly includes id: `dag:child_dag`, so edge below is
no longer dangling:
```json
{
"source_id": "trigger:parent_dag:child_dag:trigger_child_dag",
"target_id": "dag:child_dag"
}
```
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