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# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License. You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
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# KIND, either express or implied. See the License for the
# specific language governing permissions and limitations
# under the License.
from __future__ import annotations
import warnings
from typing import TYPE_CHECKING, Iterable, Sequence
from airflow.exceptions import AirflowException, RemovedInAirflow3Warning
from airflow.models.taskinstance import TaskInstance
from airflow.utils import timezone
from airflow.utils.log.logging_mixin import LoggingMixin
from airflow.utils.session import NEW_SESSION, create_session, provide_session
from airflow.utils.state import State
if TYPE_CHECKING:
from pendulum import DateTime
from sqlalchemy import Session
from airflow.models.dagrun import DagRun
from airflow.models.operator import Operator
from airflow.models.taskmixin import DAGNode
# The key used by SkipMixin to store XCom data.
[docs]XCOM_SKIPMIXIN_KEY = "skipmixin_key"
# The dictionary key used to denote task IDs that are skipped
[docs]XCOM_SKIPMIXIN_SKIPPED = "skipped"
# The dictionary key used to denote task IDs that are followed
[docs]XCOM_SKIPMIXIN_FOLLOWED = "followed"
def _ensure_tasks(nodes: Iterable[DAGNode]) -> Sequence[Operator]:
from airflow.models.baseoperator import BaseOperator
from airflow.models.mappedoperator import MappedOperator
return [n for n in nodes if isinstance(n, (BaseOperator, MappedOperator))]
[docs]class SkipMixin(LoggingMixin):
"""A Mixin to skip Tasks Instances"""
def _set_state_to_skipped(
self,
dag_run: DagRun,
tasks: Iterable[Operator],
session: Session,
) -> None:
"""Used internally to set state of task instances to skipped from the same dag run."""
now = timezone.utcnow()
session.query(TaskInstance).filter(
TaskInstance.dag_id == dag_run.dag_id,
TaskInstance.run_id == dag_run.run_id,
TaskInstance.task_id.in_(d.task_id for d in tasks),
).update(
{
TaskInstance.state: State.SKIPPED,
TaskInstance.start_date: now,
TaskInstance.end_date: now,
},
synchronize_session=False,
)
@provide_session
[docs] def skip(
self,
dag_run: DagRun,
execution_date: DateTime,
tasks: Iterable[DAGNode],
session: Session = NEW_SESSION,
):
"""
Sets tasks instances to skipped from the same dag run.
If this instance has a `task_id` attribute, store the list of skipped task IDs to XCom
so that NotPreviouslySkippedDep knows these tasks should be skipped when they
are cleared.
:param dag_run: the DagRun for which to set the tasks to skipped
:param execution_date: execution_date
:param tasks: tasks to skip (not task_ids)
:param session: db session to use
"""
task_list = _ensure_tasks(tasks)
if not task_list:
return
if execution_date and not dag_run:
from airflow.models.dagrun import DagRun
warnings.warn(
"Passing an execution_date to `skip()` is deprecated in favour of passing a dag_run",
RemovedInAirflow3Warning,
stacklevel=2,
)
dag_run = (
session.query(DagRun)
.filter(
DagRun.dag_id == task_list[0].dag_id,
DagRun.execution_date == execution_date,
)
.one()
)
elif execution_date and dag_run and execution_date != dag_run.execution_date:
raise ValueError(
"execution_date has a different value to dag_run.execution_date -- please only pass dag_run"
)
if dag_run is None:
raise ValueError("dag_run is required")
self._set_state_to_skipped(dag_run, task_list, session)
session.commit()
# SkipMixin may not necessarily have a task_id attribute. Only store to XCom if one is available.
task_id: str | None = getattr(self, "task_id", None)
if task_id is not None:
from airflow.models.xcom import XCom
XCom.set(
key=XCOM_SKIPMIXIN_KEY,
value={XCOM_SKIPMIXIN_SKIPPED: [d.task_id for d in task_list]},
task_id=task_id,
dag_id=dag_run.dag_id,
run_id=dag_run.run_id,
session=session,
)
[docs] def skip_all_except(self, ti: TaskInstance, branch_task_ids: None | str | Iterable[str]):
"""
This method implements the logic for a branching operator; given a single
task ID or list of task IDs to follow, this skips all other tasks
immediately downstream of this operator.
branch_task_ids is stored to XCom so that NotPreviouslySkippedDep knows skipped tasks or
newly added tasks should be skipped when they are cleared.
"""
self.log.info("Following branch %s", branch_task_ids)
if isinstance(branch_task_ids, str):
branch_task_id_set = {branch_task_ids}
elif isinstance(branch_task_ids, Iterable):
branch_task_id_set = set(branch_task_ids)
invalid_task_ids_type = {
(bti, type(bti).__name__) for bti in branch_task_ids if not isinstance(bti, str)
}
if invalid_task_ids_type:
raise AirflowException(
f"'branch_task_ids' expected all task IDs are strings. "
f"Invalid tasks found: {invalid_task_ids_type}."
)
elif branch_task_ids is None:
branch_task_id_set = set()
else:
raise AirflowException(
"'branch_task_ids' must be either None, a task ID, or an Iterable of IDs, "
f"but got {type(branch_task_ids).__name__!r}."
)
dag_run = ti.get_dagrun()
task = ti.task
dag = task.dag
if TYPE_CHECKING:
assert dag
valid_task_ids = set(dag.task_ids)
invalid_task_ids = branch_task_id_set - valid_task_ids
if invalid_task_ids:
raise AirflowException(
"'branch_task_ids' must contain only valid task_ids. "
f"Invalid tasks found: {invalid_task_ids}."
)
downstream_tasks = _ensure_tasks(task.downstream_list)
if downstream_tasks:
# For a branching workflow that looks like this, when "branch" does skip_all_except("task1"),
# we intuitively expect both "task1" and "join" to execute even though strictly speaking,
# "join" is also immediately downstream of "branch" and should have been skipped. Therefore,
# we need a special case here for such empty branches: Check downstream tasks of branch_task_ids.
# In case the task to skip is also downstream of branch_task_ids, we add it to branch_task_ids and
# exclude it from skipping.
#
# branch -----> join
# \ ^
# v /
# task1
#
for branch_task_id in list(branch_task_id_set):
branch_task_id_set.update(dag.get_task(branch_task_id).get_flat_relative_ids(upstream=False))
skip_tasks = [t for t in downstream_tasks if t.task_id not in branch_task_id_set]
follow_task_ids = [t.task_id for t in downstream_tasks if t.task_id in branch_task_id_set]
self.log.info("Skipping tasks %s", [t.task_id for t in skip_tasks])
with create_session() as session:
self._set_state_to_skipped(dag_run, skip_tasks, session=session)
# For some reason, session.commit() needs to happen before xcom_push.
# Otherwise the session is not committed.
session.commit()
ti.xcom_push(key=XCOM_SKIPMIXIN_KEY, value={XCOM_SKIPMIXIN_FOLLOWED: follow_task_ids})
