josh-fell opened a new issue, #35433:
URL: https://github.com/apache/airflow/issues/35433
### Body
Several Databricks operators exist which have a `json` parameter that can be
a JSON object which contains any number of API parameters. In the constructors
of these operators, the `json` value can be added to be other parameters that
can be passed to the operator like `name`, `tags`, etc.
Since `json` is a templated field, attempting to modify it in this way will
fail/not work as expected if the input arg is a string (e.g. "{{
var.json....}}" or an XComArg (meaning it's an output of a previous task).
Template fields are not rendered until just before the execute method is called.
To illustrate the point, let's use this example DAG where we define the
`json` arg in a previous task and use its output:
```py
from __future__ import annotations
from pendulum import datetime
from typing import TYPE_CHECKING, Sequence
from airflow.decorators import dag, task
from airflow.models.baseoperator import BaseOperator
if TYPE_CHECKING:
from airflow.utils.context import Context
class DatabricksCreateJobsOperator(BaseOperator):
template_fields: Sequence[str] = ("json", "databricks_conn_id")
def __init__(
self,
*,
json: dict | None = None,
name: str | None = None,
tags: dict[str, str] | None = None,
**kwargs
):
super().__init__(**kwargs)
self.json = json or {}
if name is not None:
self.json["name"] = name
if tags is not None:
self.json["tags"] = tags
def execute(context: Context) -> None:
pass
@dag(start_date=datetime(2023, 1, 1), schedule=None)
def derived_template_fields():
@task
def push_json() -> dict[str, str]:
return {"key1": "val1", "key2": "val2"}
json = push_json()
DatabricksCreateJobsOperator(
task_id="create_job_w_json", json=json, name="some_name",
tags={"key3": "value3"}
)
derived_template_fields()
```
DAG parsing fails with:
```
Running: airflow dags reserialize
[2023-08-31T14:29:57.796+0000] {utils.py:430} WARNING - No module named
'paramiko'
[2023-08-31T14:29:57.816+0000] {utils.py:430} WARNING - No module named
'airflow.providers.dbt'
[2023-08-31T14:29:58.533+0000] {dagbag.py:539} INFO - Filling up the DagBag
from /usr/local/airflow/dags
[2023-08-31T14:29:58.615+0000] {dagbag.py:347} ERROR - Failed to import:
/usr/local/airflow/dags/derived_template_fields.py
Traceback (most recent call last):
File "/usr/local/lib/python3.11/site-packages/airflow/models/dagbag.py",
line 343, in parse
loader.exec_module(new_module)
File "<frozen importlib._bootstrap_external>", line 940, in exec_module
File "<frozen importlib._bootstrap>", line 241, in
_call_with_frames_removed
File "/usr/local/airflow/dags/derived_template_fields.py", line 50, in
<module>
derived_template_fields()
File "/usr/local/lib/python3.11/site-packages/airflow/models/dag.py", line
3798, in factory
f(**f_kwargs)
File "/usr/local/airflow/dags/derived_template_fields.py", line 41, in
derived_template_fields
DatabricksCreateJobsOperator(
File
"/usr/local/lib/python3.11/site-packages/airflow/models/baseoperator.py", line
436, in apply_defaults
result = func(self, **kwargs, default_args=default_args)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/airflow/dags/derived_template_fields.py", line 27, in
__init__
self.json["name"] = name
~~~~~~~~~^^^^^^^^
TypeError: 'PlainXComArg' object does not support item assignment
```
Even if we change the `json` arg assignment to use the classic XCom Jinja
template approach (i.e. `json = "{{ ti.xcom_pull(task_ids='push_json') }}"`),
the DAG fails to parse:
```
Running: airflow dags reserialize
[2023-08-31T14:32:01.553+0000] {utils.py:430} WARNING - No module named
'paramiko'
[2023-08-31T14:32:01.574+0000] {utils.py:430} WARNING - No module named
'airflow.providers.dbt'
[2023-08-31T14:32:02.341+0000] {dagbag.py:539} INFO - Filling up the DagBag
from /usr/local/airflow/dags
[2023-08-31T14:32:02.415+0000] {dagbag.py:347} ERROR - Failed to import:
/usr/local/airflow/dags/derived_template_fields.py
Traceback (most recent call last):
File "/usr/local/lib/python3.11/site-packages/airflow/models/dagbag.py",
line 343, in parse
loader.exec_module(new_module)
File "<frozen importlib._bootstrap_external>", line 940, in exec_module
File "<frozen importlib._bootstrap>", line 241, in
_call_with_frames_removed
File "/usr/local/airflow/dags/derived_template_fields.py", line 51, in
<module>
derived_template_fields()
File "/usr/local/lib/python3.11/site-packages/airflow/models/dag.py", line
3798, in factory
f(**f_kwargs)
File "/usr/local/airflow/dags/derived_template_fields.py", line 42, in
derived_template_fields
DatabricksCreateJobsOperator(
File
"/usr/local/lib/python3.11/site-packages/airflow/models/baseoperator.py", line
436, in apply_defaults
result = func(self, **kwargs, default_args=default_args)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/airflow/dags/derived_template_fields.py", line 27, in
__init__
self.json["name"] = name
~~~~~~~~~^^^^^^^^
TypeError: 'str' object does not support item assignment
```
It would be best to move modifying json (and generally any template field)
to the execute method instead.
### Committer
- [X] I acknowledge that I am a maintainer/committer of the Apache Airflow
project.
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