ashb opened a new pull request, #45627:
URL: https://github.com/apache/airflow/pull/45627
This PR restructures the Mapped Operator and Mapped Task Group code to live
in
the Task SDK at definition time.
The big thing this change _does not do_ is make it possible to execute mapped
tasks via the Task Execution API server etc -- that is up next.
There were some un-avoidable changes to the scheduler/expansion part of
mapped
tasks here. Of note:
`BaseOperator.get_mapped_ti_count` has moved from an instance method on
BaseOperator to be a class method. The reason for this was that with the move
of more and more of the "definition time" code into the TaskSDK BaseOperator
and AbstractOperator it is no longer possible to add DB-accessing code to a
base class and have it apply to the subclasses. (i.e.
`airflow.models.abstractoperator.AbstractOperator` is now _not always_ in the
MRO for tasks. Eventually that class will be deleted, but not yet)
On a similar vein XComArg's `get_task_map_length` is also moved to a single
dispatch class method on the TaskMap model since now the definition time
objects live in the TaskSDK, and there is no realistic way to get a per-type
subclass with DB logic (i.e. it's very complex to end up with a
PlainDBXComArg, a MapDBXComArg, etc. that we can attach the method too)
For those who aren't aware, singledispatch (and singledispatchmethod) are a
part of the standard library when the type of the first argument is used to
determine which implementation to call. If you are familiar with C++ or Java
this is very similar to method overloading, the one caveat is that it _only_
examines the type of the first argument, not the full signature.
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