qcha41 opened a new issue, #27007:
URL: https://github.com/apache/airflow/issues/27007
### Apache Airflow version
Other Airflow 2 version
### What happened
Hello everyone,
I am trying to use a custom XCOM key in task mapping, other than the default
"return_value" key. This results in a ValueError :
```
ValueError: cannot map over XCom with custom key [...]
```
### What you think should happen instead
I don't understand this limitation.
### How to reproduce
```python
import datetime as dt
from airflow import DAG, XComArg
from airflow.operators.trigger_dagrun import TriggerDagRunOperator
from airflow.operators.python import PythonOperator
with DAG(
'dag_test_v1.0.0',
start_date = dt.datetime(2022, 10, 12),
) as dag:
def produce_parameters(**kwargs):
kwargs['ti'].xcom_push("my_custom_key", [{"message":1},
{"message":2}])
t1 = PythonOperator(task_id='python_task',
python_callable=produce_parameters, provide_context=True,)
t2 = TriggerDagRunOperator.partial(
task_id = 'task2',
trigger_dag_id = 'sandbox_downstream_v1.0.1'
).expand(
conf=XComArg(t1, 'my_custom_key')
)
t1 >> t2
```
```
Traceback (most recent call last):
File "dag_test.py", line 17, in <module>
t2 = TriggerDagRunOperator.partial(
File
"/usr/local/lib/python3.10/site-packages/airflow/models/mappedoperator.py",
line 179, in expand
return self._expand(DictOfListsExpandInput(mapped_kwargs), strict=False)
File
"/usr/local/lib/python3.10/site-packages/airflow/models/mappedoperator.py",
line 196, in _expand
ensure_xcomarg_return_value(expand_input.value)
File
"/usr/local/lib/python3.10/site-packages/airflow/models/mappedoperator.py",
line 133, in ensure_xcomarg_return_value
ensure_xcomarg_return_value(v)
File
"/usr/local/lib/python3.10/site-packages/airflow/models/mappedoperator.py",
line 128, in ensure_xcomarg_return_value
raise ValueError(f"cannot map over XCom with custom key {key!r} from
{operator}")
ValueError: cannot map over XCom with custom key 'my_custom_key' from
<Task(PythonOperator): python_task>
```bash
### Operating System
Debian 11
### Versions of Apache Airflow Providers
_No response_
### Deployment
Virtualenv installation
### Deployment details
_No response_
### Anything else
_No response_
### Are you willing to submit PR?
- [ ] 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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