Deleting associated objects

Summary

In this lesson, we addressed a data cleanup issue in our blog application. Currently, when an article is deleted, its associated comments remain in the database without an article reference. To prevent orphaned comments, we implemented a beforeDestroy lifecycle callback in Sails.

The beforeDestroy lifecycle callback runs automatically before an article is deleted. Inside this callback, we:

1. Retrieved the ID of the article being deleted.

2. Used this ID to find and delete all associated comments.

3. Logged the deleted comments to verify the cleanup process.

We tested the implementation by creating an article, adding multiple comments, and then deleting the article. The logs confirmed that all associated comments were successfully removed.

Sails supports lifecycle callbacks for create, update, and destroy operations, allowing developers to run logic before or after these actions. In this case, we used beforeDestroy to ensure that deleting an article also deletes its comments, keeping our database clean. 🚀

Transcript

Okay, so right now in our article, we have a little bit of a problem. It's not really a big problem, but I tend to want to make things cleaner as I develop.

So one thing you'd notice is, okay, if I go start up the Sails server... back to Firefox. So one thing you'd notice is we are going to be having comments, right? In our article.

So the dominoes say, hello. And yeah, so, and so forth. So now what happens when we delete this article? What happens to the comments?

So let's say we have like 2000 comments. What happens to those comments? Well, they are not going to have any article associated with them, that's for sure.

But they are still going to be in our database. How about we clean that up? So what we want to do is that before we delete an article or we destroy an article, we want to destroy every comment associated with that article.

Okay? So how do we do that? All right. One way is to do it in the action, right? So you're going to write some business logic to destroy all the comments in the action.

But Sails has something called lifecycle callbacks for our models.

So this gives us access to running code before or after some model method. We're gonna use one of those lifecycle callbacks called beforeDestroy.

All right, so let's go back to Visual Studio Code. And here we are in our article model.

So we're gonna come out of the attributes and write a beforeDestroy method.

This method is a function. It takes in a criteria and a proceed callback.

The criteria tells us which record is being deleted, and the proceed callback tells Sails that we are done with our custom logic and it can proceed with the deletion.

So what's in this criteria? Let’s just log that out so we can see for ourselves. Instead of me telling you, we’ll log the criteria and then proceed.

Let’s save that, restart the server, and go back to Firefox. Now, when we delete an article, we should see some logs.

Okay, yeah, so I messed up the spelling—it should be beforeDestroy instead of "beforeDestroyAll."

Let’s fix that, save it, and restart the server again.

Now, go back to Firefox and delete this article. We should see some server logs.

And now you can see the criteria logged in the console.

The interesting part is that we have this where property that gives us the ID of the article being deleted.

With this, we can find all comments that have this article ID and delete them.

So let’s do that.

Instead of logging the criteria, we’ll:

• Use await Comment.destroy()

• Pass in { article: criteria.where.id } to delete all associated comments

• Use .fetch() to log the deleted comments

Now, let’s restart the server and go back to Firefox.

We'll create a new article:

• Title: "Sails is amazing"

• Body: "Hello, Sails is amazing. Did you know?"

Now, let’s add some comments:

Now that we have several comments, let’s delete the article.

If everything works correctly, we should see logs of the deleted comments.

Go back to Firefox, click Delete, and yes! 🎉 All the comments were destroyed.

So, this lifecycle callback is a nifty way to run code before or after a model method.

Sails provides before and after lifecycle callbacks for the following methods:

• beforeCreate, afterCreate

• beforeUpdate, afterUpdate

• beforeDestroy, afterDestroy

In this case, we used beforeDestroy to delete associated comments before deleting an article, keeping our database clean.

We don’t need the log anymore, so let’s remove it.

And that's it! Now, every time an article is deleted, its comments are deleted too.