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"""Example DAG demonstrating the usage DAG params to model a trigger UI with a user form.
This example DAG generates greetings to a list of provided names in selected languages in the logs.
"""
from __future__ import annotations
import datetime
from pathlib import Path
from typing import TYPE_CHECKING
from airflow.decorators import task
from airflow.models.dag import DAG
from airflow.models.param import Param
from airflow.utils.trigger_rule import TriggerRule
if TYPE_CHECKING:
from airflow.models.dagrun import DagRun
from airflow.models.taskinstance import TaskInstance
with DAG(
dag_id=Path(__file__).stem,
dag_display_name="Params Trigger UI",
description=__doc__.partition(".")[0],
doc_md=__doc__,
schedule=None,
start_date=datetime.datetime(2022, 3, 4),
catchup=False,
tags=["example", "params"],
params={
"names": Param(
["Linda", "Martha", "Thomas"],
type="array",
description="Define the list of names for which greetings should be generated in the logs."
" Please have one name per line.",
title="Names to greet",
),
"english": Param(True, type="boolean", title="English"),
"german": Param(True, type="boolean", title="German (Formal)"),
"french": Param(True, type="boolean", title="French"),
},
) as dag:
@task(task_id="get_names", task_display_name="Get names")
[docs] def get_names(**kwargs) -> list[str]:
ti: TaskInstance = kwargs["ti"]
dag_run: DagRun = ti.dag_run
if "names" not in dag_run.conf:
print("Uuups, no names given, was no UI used to trigger?")
return []
return dag_run.conf["names"]
@task.branch(task_id="select_languages", task_display_name="Select languages")
def select_languages(**kwargs) -> list[str]:
ti: TaskInstance = kwargs["ti"]
dag_run: DagRun = ti.dag_run
selected_languages = []
for lang in ["english", "german", "french"]:
if lang in dag_run.conf and dag_run.conf[lang]:
selected_languages.append(f"generate_{lang}_greeting")
return selected_languages
@task(task_id="generate_english_greeting", task_display_name="Generate English greeting")
def generate_english_greeting(name: str) -> str:
return f"Hello {name}!"
@task(task_id="generate_german_greeting", task_display_name="Erzeuge Deutsche Begrüßung")
def generate_german_greeting(name: str) -> str:
return f"Sehr geehrter Herr/Frau {name}."
@task(task_id="generate_french_greeting", task_display_name="Produire un message d'accueil en français")
def generate_french_greeting(name: str) -> str:
return f"Bonjour {name}!"
@task(task_id="print_greetings", task_display_name="Print greetings", trigger_rule=TriggerRule.ALL_DONE)
def print_greetings(greetings1, greetings2, greetings3) -> None:
for g in greetings1 or []:
print(g)
for g in greetings2 or []:
print(g)
for g in greetings3 or []:
print(g)
if not (greetings1 or greetings2 or greetings3):
print("sad, nobody to greet :-(")
lang_select = select_languages()
names = get_names()
english_greetings = generate_english_greeting.expand(name=names)
german_greetings = generate_german_greeting.expand(name=names)
french_greetings = generate_french_greeting.expand(name=names)
lang_select >> [english_greetings, german_greetings, french_greetings]
results_print = print_greetings(english_greetings, german_greetings, french_greetings)