turbaszek commented on a change in pull request #8805:
URL: https://github.com/apache/airflow/pull/8805#discussion_r422638768
##########
File path: airflow/models/baseoperator.py
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@@ -60,9 +60,25 @@
ScheduleInterval = Union[str, timedelta, relativedelta]
+class BaseOperatorMeta(type):
+ """
+ Base metaclass of BaseOperator.
+ """
+ def __call__(cls, *args, **kwargs):
+ """
+ Called when you call BaseOperator(). In this way we are able to
perform an action
+ after initializing an operator no matter where the
``super().__init__`` is called
+ (before or after assign of new attributes in a custom operator).
+ """
+ obj = type.__call__(cls, *args, **kwargs)
+ # Set upstream task defined by XComArgs passed to template fields of
an operator
+ obj._set_xcomargs_dependencies() # pylint: disable=protected-access
Review comment:
> meta_class introduce backward compatibility problems for users who
already have metaclass defined for their operator ( they will have to inherit
from BaseOperatorMeta)
True
> what happens when a user creates an operator without DAG?
Well, nothing. If the question is about
https://github.com/apache/airflow/pull/8805#discussion_r422633456 then
AirflowException on missing DAG is raised. I've added a test for that.
> 1. we can fix set_upstream
Is this related to this comment
https://github.com/apache/airflow/pull/8805#discussion_r422633321 ?
> 2. we can just finalize Operator implementation when we add it to dag (
thus no metaclass is required)
User can either provide the `dag` argument to operator or if it's `None`
then we call `DagContext.get_current_dag()` . And setting DAG (via
`@dag.setter`) is done during `__init__` call, so I'm not sure if I understand
when the "add to dag" moment happens.
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