airflow/example_dags/example_nested_branch_dag.py

#
# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements.  See the NOTICE file
# distributed with this work for additional information
# 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.
"""
Example DAG demonstrating a workflow with nested branching. The join tasks are created with
``none_failed_min_one_success`` trigger rule such that they are skipped whenever their corresponding
branching tasks are skipped.
"""
from __future__ import annotations

import pendulum

from airflow.decorators import task
from airflow.models import DAG
from airflow.operators.empty import EmptyOperator
from airflow.utils.trigger_rule import TriggerRule

with DAG(
    dag_id="example_nested_branch_dag",
    start_date=pendulum.datetime(2021, 1, 1, tz="UTC"),
    catchup=False,
    schedule="@daily",
    tags=["example"],
) as dag:

    @task.branch()
    def branch(task_id_to_return: str) -> str:
        return task_id_to_return

    branch_1 = branch.override(task_id="branch_1")(task_id_to_return="true_1")
    join_1 = EmptyOperator(task_id="join_1", trigger_rule=TriggerRule.NONE_FAILED_MIN_ONE_SUCCESS)
    true_1 = EmptyOperator(task_id="true_1")
    false_1 = EmptyOperator(task_id="false_1")

    branch_2 = branch.override(task_id="branch_2")(task_id_to_return="true_2")
    join_2 = EmptyOperator(task_id="join_2", trigger_rule=TriggerRule.NONE_FAILED_MIN_ONE_SUCCESS)
    true_2 = EmptyOperator(task_id="true_2")
    false_2 = EmptyOperator(task_id="false_2")
    false_3 = EmptyOperator(task_id="false_3")

    branch_1 >> true_1 >> join_1
    branch_1 >> false_1 >> branch_2 >> [true_2, false_2] >> join_2 >> false_3 >> join_1