[GitHub] ybendana opened a new pull request #4291: [AIRFLOW-1488] Add the DagRunSensor operator

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ybendana opened a new pull request #4291: [AIRFLOW-1488] Add the DagRunSensor operator
URL: https://github.com/apache/incubator-airflow/pull/4291
 
 
   ExternalTaskSensor allows one to wait on any valid combination of
   (dag_id, task_id). It is desirable though to be able to wait on entire
   DagRuns, as opposed to specific task instances in those DAGs.
   
   This pull request adds a new sensor in contrib called DagRunSensor.
   This version is a different approach from previous pull requests
   addressing the same issue.  In this case, the DagRunSensor takes a
   trigger_task_id, the id of a task that triggers DagRuns.  The trigger
   task returns a list of run_ids of the DagRuns it triggered and the
   DagRunSensor polls their status. For this purpose the
   TriggerDagRunOperator was modified so that it stores the run_id of the
   triggered DagRun.
   
   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.
   
   ### Description
   
   - [ ] Here are some details about my PR, including screenshots of any UI changes:
   See the above description.  I also copied quite a bit from the previous pull requests on this issue #2500 and #3234.  Unlike those attempts, the focus here is on triggered DagRuns.  I realize it may not be generally applicable to everyone's workflows but it has been very useful for us. At one point I considered using subdags but since they have had their issues I think this a good alternative.
   
   ### Tests
   
   - [ ] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason:
   I included test_dagrun_sensor.py and test_dagrun_sensor_dag.py.  Currently, I'm running into an issue executing the test in the Docker environment because the sensor task has to wait on the triggered DagRun.  The DagRun is triggered but is never scheduled.  I think this is because the unit test uses the SequentialExecutor and SQLite.  If I run the scheduler manually, the triggered DagRun executes. I'm not sure what to do about this. For now, I've commented the successful DagRun test and have only the failed DagRun test active.
   
   ### Commits
   
   - [ ] 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
   
   - [ ] In case of new functionality, my PR adds documentation that describes how to use it.
     - When adding new operators/hooks/sensors, the autoclass documentation generation needs to be added.
     - All the public functions and the classes in the PR contain docstrings that explain what it does
   
   ### Code Quality
   
   - [ ] Passes `flake8`
   

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