[GitHub] [airflow] uranusjr commented on pull request #16931: #16692 show cron description in UI

[GitBox <gi...@apache.org>]

uranusjr commented on pull request #16931:
URL: https://github.com/apache/airflow/pull/16931#issuecomment-882368742


   > we can create a base class like DagBase which will have the common properties, but I think it's a overkill but a better approach so applying this.
   
   The problem is, we are planning to make `timetable` directly customisable by the user like this:
   
   ```python
   class MyCustomTimetable(Timetable):
       ...
   
   dag = DAG(
       ...,
       timetable=MyCustomTimetable(),
   )
   ```
   
   and this can be any rich Python object. So while the `BaseDag` approach works right now, it will not work once the timetable instance is not calculated directly from `schedule_interval`. So we need to access the original `DAG.timetable` property instead.
   
   This is actually not difficult at all. All the DAG objects are in `current_app.dag_bag`, so you can add this to the template’s context:
   
   ```python
   'dag_timetable': current_app.dag_bag.get_dag(dag.dag_id).timetable
   ```
   
   But it is pretty cumbersome to add this for *all* views that render `dag.html` (because this is a base template inherited by many), and even more difficult to do for `dags.html`. So I’m thinking we probably need to expose `current_app.dag_bag` in the template instead, maybe by poplating `dag_bag` into the global Jinja environment (with e.g. `current_app.jinja_env.add_template_global()`), or something else. I’m unfortuantely not familiar with Flask enough to know the best practice.


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