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# regarding copyright ownership. The ASF licenses this file
# 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
# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
# KIND, either express or implied. See the License for the
# specific language governing permissions and limitations
# under the License.
from typing import Iterable, Union
from airflow.models.taskinstance import TaskInstance
from airflow.utils import timezone
from airflow.utils.log.logging_mixin import LoggingMixin
from airflow.utils.session import create_session, provide_session
from airflow.utils.state import State
# 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"
[docs]class SkipMixin(LoggingMixin):
"""A Mixin to skip Tasks Instances"""
[docs] def _set_state_to_skipped(self, dag_run, execution_date, tasks, session):
"""Used internally to set state of task instances to skipped from the same dag run."""
task_ids = [d.task_id for d in tasks]
now = timezone.utcnow()
if dag_run:
session.query(TaskInstance).filter(
TaskInstance.dag_id == dag_run.dag_id,
TaskInstance.execution_date == dag_run.execution_date,
TaskInstance.task_id.in_(task_ids),
).update(
{
TaskInstance.state: State.SKIPPED,
TaskInstance.start_date: now,
TaskInstance.end_date: now,
},
synchronize_session=False,
)
else:
if execution_date is None:
raise ValueError("Execution date is None and no dag run")
self.log.warning("No DAG RUN present this should not happen")
# this is defensive against dag runs that are not complete
for task in tasks:
ti = TaskInstance(task, execution_date=execution_date)
ti.state = State.SKIPPED
ti.start_date = now
ti.end_date = now
session.merge(ti)
@provide_session
[docs] def skip(
self,
dag_run,
execution_date,
tasks,
session=None,
):
"""
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
"""
if not tasks:
return
self._set_state_to_skipped(dag_run, execution_date, tasks, session)
session.commit()
# SkipMixin may not necessarily have a task_id attribute. Only store to XCom if one is available.
try:
task_id = self.task_id # noqa
except AttributeError:
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 tasks]},
task_id=task_id,
dag_id=dag_run.dag_id,
execution_date=dag_run.execution_date,
session=session,
)
[docs] def skip_all_except(self, ti: TaskInstance, branch_task_ids: Union[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_ids = {branch_task_ids}
branch_task_ids = set(branch_task_ids)
dag_run = ti.get_dagrun()
task = ti.task
dag = task.dag
downstream_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_ids):
branch_task_ids.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_ids]
follow_task_ids = [t.task_id for t in downstream_tasks if t.task_id in branch_task_ids]
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, ti.execution_date, 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})