[GitHub] [airflow] BasPH opened a new pull request #5056: [WIP][AIRFLOW-???] Move remaining models out of models.py

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

BasPH opened a new pull request #5056: [WIP][AIRFLOW-???] Move remaining models out of models.py
URL: https://github.com/apache/airflow/pull/5056
 
 
   **Currently draft!**
   My own CI is green on all Python 3 jobs, Python 2 jobs are in progress. Made this draft PR because I have some questions to be answered before merging.
   
   ------
   
   This PR finalizes the move of all classes out of the infamous models.py (including test_models.py). It's a big PR since all classes are tightly coupled which made it impossible to move out one by one. Some of the non-straight-forward things to point out:
   
   - To preserve backwards compatibility, `airflow/models/__init__.py` imports all (sub)modules (So you can still import `airflow.models.DAG` instead of `airflow.models.dag.DAG`).
   - Classes `DAG` and `DagModel` are in the same file since they both depend on the `get_last_dagrun()` function.
   - I placed classes and variables related to fernet in `airflow/models/crypto.py`.
   - I had to fix (i.e. disentangle) several weird imports along the way which broke and didn't make sense. Mostly related to `airflow.models` importing absolutely everything in the Airflow project, and other files depending on the import in `airflow.models` instead of the actual module. Some examples:
   	- `AirflowException` was imported in `airflow/models/__init__.py` and multiple other files imported from `airflow.models` while it's defined in `airflow.exceptions`.
   	- Same for TriggerRule, this was imported in `airflow/models/__init__.py` and multiple other files imported TriggerRule from there. However, it's defined in `airflow.utils.trigger_rule.TriggerRule`, so I removed it from models and corrected those imports.
   	- Same for `airflow.utils.timezone`.
   	- `tests/test_models.py` turned out to import `State` twice, once via `from airflow.models import State as ST` and once via `from airflow.utils.state import State`. I removed the `ST` import.
   	- Some mocks had to be changed because you have to mock from the location where you use the function/var/whatever. For example, in tests/test_models.py:TaskInstanceTest.test_email_alert I had to change `@patch('airflow.models.send_email')` into `@patch('airflow.models.taskinstance.send_email')` because it's now called from there and not airflow.models.
   - The `global _CONTEXT_MANAGER_DAG` gave some trouble because a global cannot be shared over multiple files, which made it impossible to split the BaseOperator and DAG. So, I placed the `_CONTEXT_MANAGER_DAG` in airflow/settings.py, and simply import from there. The added benefit is that `global` isn't even needed! Bye bye global :-) More info: https://stackoverflow.com/a/13034908/3066428
   
   I have 3 questions:
   
   1. Since this PR related to AIRFLOW-3456, AIRFLOW-3460, AIRFLOW-3465, AIRFLOW-3466, AIRFLOW-3470, AIRFLOW-3473 and AIRFLOW-3579, what title should I give the PR? Perhaps we could make a parent JIRA issue and place all these items as subissues. @Fokko any thoughts?
   2. In the previous moves we did not preserve backwards compatibility, i.e. models are not imported in airflow.models, instead you now have to do e.g. `from airflow.models.slamiss import SlaMiss`. Should we fix these and import all not-imported models in `airflow.models` after all? And if so: in this PR or separate PR?
   3. Classes `DAG` and `DagModel` are in the same file since they both depend on the `get_last_dagrun()` function. Any strong opinions on keeping it this way, or moving the `get_last_dagrun()` function elsewhere so we can split `DAG` and `DagModel`?
   
   ---------
   
   Make sure you have checked _all_ steps below.
   
   ### Jira
   
   - [ ] My PR addresses the following [Airflow Jira](https://issues.apache.org/jira/browse/AIRFLOW/) issues and references them in the PR title. For example, "\[AIRFLOW-XXX\] My Airflow PR"
     - https://issues.apache.org/jira/browse/AIRFLOW-XXX
     - In case you are fixing a typo in the documentation you can prepend your commit with \[AIRFLOW-XXX\], code changes always need a Jira issue.
     - In case you are proposing a fundamental code change, you need to create an Airflow Improvement Proposal ([AIP](https://cwiki.apache.org/confluence/display/AIRFLOW/Airflow+Improvements+Proposals)).
     - In case you are adding a dependency, check if the license complies with the [ASF 3rd Party License Policy](https://www.apache.org/legal/resolved.html#category-x).
   
   ### Description
   
   - [x] Here are some details about my PR, including screenshots of any UI changes:
   
   See above.
   
   ### Tests
   
   - [x] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason:
   
   No new tests, only split tests/test_models.py into modules corresponding to airflow.models.
   
   ### Commits
   
   - [x] My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "[How to write a good git commit message](http://chris.beams.io/posts/git-commit/)":
     1. Subject is separated from body by a blank line
     1. Subject is limited to 50 characters (not including Jira issue reference)
     1. Subject does not end with a period
     1. Subject uses the imperative mood ("add", not "adding")
     1. Body wraps at 72 characters
     1. Body explains "what" and "why", not "how"
   
   ### Documentation
   
   - [x] In case of new functionality, my PR adds documentation that describes how to use it.
     - All the public functions and the classes in the PR contain docstrings that explain what it does
     - If you implement backwards incompatible changes, please leave a note in the [Updating.md](https://github.com/apache/airflow/blob/master/UPDATING.md) so we can assign it to a appropriate release
   
   ### Code Quality
   
   - [x] Passes `flake8`
   

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