Source code for airflow.triggers.base
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from __future__ import annotations
import abc
from typing import Any, AsyncIterator
from airflow.utils.log.logging_mixin import LoggingMixin
[docs]class BaseTrigger(abc.ABC, LoggingMixin):
"""
Base class for all triggers.
A trigger has two contexts it can exist in:
- Inside an Operator, when it's passed to TaskDeferred
- Actively running in a trigger worker
We use the same class for both situations, and rely on all Trigger classes
to be able to return the arguments (possible to encode with Airflow-JSON) that will
let them be re-instantiated elsewhere.
"""
def __init__(self, **kwargs):
# these values are set by triggerer when preparing to run the instance
# when run, they are injected into logger record.
self.task_instance = None
self.trigger_id = None
def _set_context(self, context):
"""Part of LoggingMixin and used mainly for configuration of task logging; not used for triggers."""
raise NotImplementedError
@abc.abstractmethod
[docs] def serialize(self) -> tuple[str, dict[str, Any]]:
"""
Return the information needed to reconstruct this Trigger.
:return: Tuple of (class path, keyword arguments needed to re-instantiate).
"""
raise NotImplementedError("Triggers must implement serialize()")
@abc.abstractmethod
[docs] async def run(self) -> AsyncIterator[TriggerEvent]:
"""
Run the trigger in an asynchronous context.
The trigger should yield an Event whenever it wants to fire off
an event, and return None if it is finished. Single-event triggers
should thus yield and then immediately return.
If it yields, it is likely that it will be resumed very quickly,
but it may not be (e.g. if the workload is being moved to another
triggerer process, or a multi-event trigger was being used for a
single-event task defer).
In either case, Trigger classes should assume they will be persisted,
and then rely on cleanup() being called when they are no longer needed.
"""
raise NotImplementedError("Triggers must implement run()")
yield # To convince Mypy this is an async iterator.
[docs] async def cleanup(self) -> None:
"""
Cleanup the trigger.
Called when the trigger is no longer needed, and it's being removed
from the active triggerer process.
This method follows the async/await pattern to allow to run the cleanup
in triggerer main event loop. Exceptions raised by the cleanup method
are ignored, so if you would like to be able to debug them and be notified
that cleanup method failed, you should wrap your code with try/except block
and handle it appropriately (in async-compatible way).
"""
[docs] def __repr__(self) -> str:
classpath, kwargs = self.serialize()
kwargs_str = ", ".join(f"{k}={v}" for k, v in kwargs.items())
return f"<{classpath} {kwargs_str}>"
[docs]class TriggerEvent:
"""
Something that a trigger can fire when its conditions are met.
Events must have a uniquely identifying value that would be the same
wherever the trigger is run; this is to ensure that if the same trigger
is being run in two locations (for HA reasons) that we can deduplicate its
events.
"""
def __init__(self, payload: Any):
self.payload = payload
[docs] def __repr__(self) -> str:
return f"TriggerEvent<{self.payload!r}>"
[docs] def __eq__(self, other):
if isinstance(other, TriggerEvent):
return other.payload == self.payload
return False
