Okay, here is the blog post about adding XCom to DAG runs in Airflow, written in a conversational and informal style, just like the example:
So I was messing around with Airflow, trying to get some data passed between tasks in my DAG. Turns out, it’s not as straightforward as you might think. But don’t worry, I figured it out, and I’m gonna share how I did it, step by step.
What’s the Deal with XCom?
Basically, XCom is like a little mailbox that your tasks can use to send messages to each other. Each message, or XCom, has a “key” (kind of like a name), and it’s linked to the task and the DAG that sent it. And, of course, it has a value, which can be anything you want, as long as it can be serialized.
My First Try: `xcom_push` and `xcom_pull`
Airflow has these built-in methods, `xcom_push` and `xcom_pull`, that sound like they should do the trick. My first thought was to use `xcom_push` in one task to send the data, and then `xcom_pull` in another task to get it. And guess what? If your task returns a value, Airflow automatically pushes it to an XCom named `return_value`. How convenient!
Here is how it works, in my task where I want to push data, I make sure the function for the task returns the value. I don’t need to explicitly use `xcom_push`.
And in the task where I want to pull the data, I just need to use `xcom_pull`. I can specify the `task_ids` to pull from a specific task, and `key` for the XCom key. The default key is `return_value`.
Getting Fancy: `DummyOperator` and `*()`
But what if I wanted to push a value without returning it, or push a different key? I found that some folks online were using a `DummyOperator` as a placeholder, and then setting the XCom directly using `*.set()`. So I gave that a shot.
I created a `DummyOperator` task right before the task where I need to access the XCom. Then, inside my code, I used `*()` to directly store the value I wanted, with a custom key. It felt a bit hacky, but it worked!
Deleting XComs
Here’s another thing I learned. These XComs can pile up, and you might want to clean them up after your DAG finishes. There is even a discussion online about how to delete them.
- I found that you can delete XComs in the Airflow UI manually. There is an XComs tab in the Admin section where you can see all XComs and delete them.
- If you want to do it in code, you can use a database query. It’s a bit complex though, I am still learning about it.
Custom XCom Backends?
And get this – there’s even a way to create your own custom XCom backends! I saw some talk about it in the Airflow documentation. Apparently, you can change the ‘xcom_backend’ configuration. I haven’t tried this myself yet, but it sounds pretty advanced. Maybe one day I will try to make sense of it. Who knows?
Wrapping Up
So, there you have it. That’s how I figured out how to add XCom to my DAG runs in Airflow. It took a bit of trial and error, but I got there in the end. Hopefully, my little adventure can help you out if you’re stuck on the same problem. Remember, `xcom_push` and `xcom_pull` are your friends, `DummyOperator` with `*()` is your secret weapon, and cleaning up XComs is a good habit. Happy coding!
Original article by the Author:Williams,If you intend to republish this content, please attribute the source accordingly:https://www.suntrekenergy.com/6739.html
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