CODEWITHSUNDEEP
firebasegoogle-cloud-firestore
frantovar
frantovar

Reputation: 561

What's the best way to delete collections and subcollections on Firestore?

I have a Firestore structure with nested subcollections like this:

So I have the following use cases:

1. When I delete an Observation I need to remove the associated image from the Storage.

2. When I delete a Visit I need to delete all it's Observations and their respective images.

3. When I delete a Project I need to delete all it's Visits, then all it's Observations and their respective images.

I'm aware that resolving the use cases 2 and 3 in the client is not a good option based on the Firebase Team recommendations so it should be resolved using Cloud Functions, right?

According to official documentation deleting a collection and all it's subcollections can be done using firebase_tools.firestore.delete but I think this solution will not satisfy the use case 1, I'm right? (Also I'm reading that using firebase_tools will lag a lot).

Another option could be doing the iteration in the Cloud and delete every item there.

I don't have too much experience with Firebase so I really don't know what's the best approach to solve this problem...

Thanks in advance!

Upvotes: 3

Views: 1481

Answers (2)

Jay
Jay

Reputation: 35648

As stated in the current documentation, deleting from the client is not advised. However, that statement is a bit of an absolute and really needs clarity; it's very use case dependent.

The big picture from Firebase:

There is no single operation in the API to delete an entire collection. Instead a collection comes into existence once a first document is added to it, and a collection disappears once the final document is deleted from it.

So, deleting via the client is possible and is sometimes a solution

HOWEVER, a clear understanding of the ramifications is important. There are many but here are some to consider:

Deleting a collection requires deleting the documents. In some cases that would mean downloading ALL of the documents to get their path which could overwhelm the device.

Along with that, a big download could drive up costs along with possibly affecting the user experience.

To be clear

deleting a collection is ok but may not scale well depending on the size of the collection

e.g. if you need to delete a collection that has 10 documents and will not scale, no problem. But if that collection scales to 1M documents that's a different use case and has a different solution.

So wrapping back to the question:

  1. When I delete an Observation I need to remove the associated image from the Storage.

The key here is "an observation" meaning 1. Yes, it is perfectly acceptable to delete this from the client as '1' is well... '1' and does not scale.

  1. When I delete a Visit I need to delete all it's Observations and their respective images.

This is use case dependent: as of now you're getting all the documents and deleting via iteration. That's what should be avoided because it doesn't scale with an open ended number of documents ...but... if you've limited visits to say 100, then it's not going to scale past that so deleting from the client is ok. If there is NO limit, then deleting from a cloud function is the way to go.

  1. When I delete a Project I need to delete all it's Visits, then all it's Observations and their respective images.

This really depends on what limits you've set for the data within a Project. If it's limited to X number of documents and X is a reasonable number then deleting from the client is okay. However, if there are no limits, leveraging cloud functions is your best bet.

There is NO reason why the two can't be combined as well. For 1, delete from the client. For 2 & 3 delete via cloud functions if the data can scale to a large number.

All that being said, Cloud functions have limitations too - the call can take a while so if there are client side queries running, you can end up with fragmented data. Also, you don't have a status or control over the length of time it will take so it could conceivably time out, then you're in a weird state with some stuff deleted and some stuff not.

Lastly, the cloud based deletions are not transactional, so some data may be deleted and some may not. That should be very very rare but the potential exists.

Upvotes: 4

Victor Eronmosele
Victor Eronmosele

Reputation: 7686

You should do the delete operations using Cloud Functions.

And there's no problem with the first use case as you can still delete a collection or a firebase storage image with Cloud Functions.

Upvotes: 1

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