![]() The second, much easier method is by opening Airflow’s homepage and going to Admin - XComs: Image 2 - Pushed XCom on Airflow backend (image by author) You can see the returned value stored in. The first one is by issuing a SQL statement in Airflow’s metadata database. It would be great to see Airflow or Apache separate Airflow-esque task dependency into its own microservice, as it could be expanded to provide dependency management across all of your systems, not just Airflow. So far, in the Airflow XCom example, weve seen how to share data between tasks using the PythonOperator, which is the most popular operator in Airflow. There are two ways to test if the value was pushed to Airflow’s XComs. If you want to pass an xcom to a bash operator in airflow 2 use env lets say you have. From left to right, The key is the identifier of your XCom. Pythonoperator import PythonOperator def printcontext(ds. You can think of an XCom as a little object with the following fields: that is stored IN the metadata database of Airflow. Tasks with dependencies on this legacy replication service couldn’t use Task Sensors to check if their data is ready. Yes XComs What is an Airflow XCom XCom stands for cross-communication and allows to exchange messages or small amount of data between tasks. While external services can GET Task Instances from Airflow, they unfortunately can’t POST them. The python operator return the output as string e.g. ![]() However, what if the upstream dependency is outside of Airflow? For example, perhaps your company has a legacy service for replicating tables from microservices into a central analytics database, and you don’t plan on migrating it to Airflow. You could use this to ensure your Dashboards and Reports wait to run until the tables they query are ready. Even better, the Task Dependency Graph can be extended to downstream dependencies outside of Airflow! Airflow provides an experimental REST API, which other applications can use to check the status of tasks. The External Task Sensor is an obvious win from a data integrity perspective. Sql="SELECT * FROM table WHERE created_at_month = '`", # Run SQL in BigQuery and export results to a tableįrom _operator import BigQueryOperatorĭestination_dataset_table='', SELECT value FROM xcom WHERE dag_id='' AND task_id='' AND. Xcom_values: List = list(map(lambda xcom: xcom.value, xcoms))ĭo note that since it is importing airflow packages, it still requires working airflow installation on python classpath (as well as connection to backend-db), but here we are not creating any tasks or dags (this snippet can be run in a standalone python file)įor this snippet, I have referred to views.py which is my favorite place to peek into Airflow's SQLAlchemy magicĭirectly query Airflow's SQLAlchemy backend meta-db XCom.execution_date = execution_date).all() XCom.dag_id = dag_id, XCom.task_id = task_id, Xcoms: List = session.query(XCom).filter( :param session: Airflow's SQLAlchemy Session (this param must not be passed, it will be automatically supplied decorator) Session: Optional) -> List:įunction that reads and returns 'values' of XCOMs with given filters Here's an untested code snippet for referenceįrom import provide_sessionįrom pendulum import read_xcom_values(dag_id: str, with this work for additional informationLearning Airflow XCom is no trivial. (without having to create a task or DAG). inside a PythonOperator 19 Mar,2017 Airflow comes with a number of example. So you want to access XCOM outside Airflow (probably a different project / module, without creating any Airflow DAGs / tasks)?Īirflow uses SQLAlchemy for mapping all it's models (including XCOM) to corresponding SQLAlchemy backend (meta-db) tables Now I would like to pass this value to some python function sql_file_template without using PythonOperator.Īs per Airflow documentation xcom can be accessed only between tasks. The output of stored proc is a string which is captured using xcom. Task_instance.xcom_push(key='query_string', value=result) ![]() Query = query.format(kwargs,kwargs ,kwargs,kwargs,kwargs) I have a stored XCom value that I wanted to pass to another python function which is not called using PythonOperator.
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