Sapphirewhale opened a new issue, #75172:
URL: https://github.com/apache/airflow/issues/75172
### Under which category would you file this issue?
Providers
### Apache Airflow version
3.3.1
### What happened and how to reproduce it?
When writing an airflow dag using a mapped task group with
TriggerDagOperator child tasks, setting the trigger_dag_id parameter on the
TriggerDagOperator causes a serialization error on running `airflow dags
reserialize` (notably the DAG parses successfully).
Example DAG:
```python
from datetime import datetime
from airflow.sdk import task_group, DAG
from airflow.operators.trigger_dagrun import TriggerDagRunOperator
with DAG(
dag_id='expand_task_group_serialization_error',
start_date=datetime(2026, 1, 1)
schedule=None,
) as dag:
@task_group(group_id="test_expanding_task_group")
def trigger_one(dag_id):
TriggerDagRunOperator(
task_id="trigger",
trigger_dag_id=dag_id
)
trigger_one.expand(dag_id=["dag_id_1", "dag_id_2"]
```
Loading the above code into the airflow DAGs directory and running `airflow
dags reserialize` throws:
```
airflow.exceptions.SerializationError: Failed to serialize DAG
'expand_task_group_serialization_error': cannot use
'airflow.serialization.dag_dependency.DagDependency' as a set element
(unhashable type: 'MappedArgument')
```
### What you think should happen instead?
Airflow should not throw the above error when serializing the DAG.
This looks to me like it's a result of the MappedArgument for trigger_dag_id
passed from the expanded task group being used to create a DagDependency
object. TriggerDagRunOperator.partioal(...).expand(...) seems to automatically
handle this case, as setting the trigger_dag_id as part of the expand call
works fine there.
Whatever mechanism is in use there to avoid the DagDependency being created
with an unserializable DAG ID should probably be replicated when a
MappedArgument is passed directly to the constructor, but I wasn't able to find
the code responsible for this.
### Operating System
Red Hat Enterprise Linux
### Deployment
Docker-Compose
### Apache Airflow Provider(s)
standard
### Versions of Apache Airflow Providers
apache-airflow-providers-standard==1.17.0
### Official Helm Chart version
Not Applicable
### Kubernetes Version
Not Applicable
### Helm Chart configuration
Not Applicable
### Docker Image customizations
Not Applicable
### Anything else?
_No response_
### Are you willing to submit PR?
- [x] Yes I am willing to submit a PR!
### Code of Conduct
- [x] I agree to follow this project's [Code of
Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)
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