Make Databricks operators' json parameter compatible with XComs, Jinja expression values #35433
Description
Body
A few 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:
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.
Currently this impacts the following operators:
- DatabricksCreateJobsOperator
- DatabricksSubmitRunOperator
- DatabricksRunNowOperator
Committer
- I acknowledge that I am a maintainer/committer of the Apache Airflow project.