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I am trying to get the UID within an onWrite cloud function of any authenticated user who deletes a document in firestore (not the real time database which doesn't have this issue). The reason is... I am trying to create a log of all actions performed on documents in a collection. I have to use cloud functions as the client could hypothetically create/edit/delete a document and then prevent the corresponding log entry from being sent.

I have seen in other stackoverflow questions like:

That firestore will not include any auth data for firestore in the onWrite function, and that the accepted workaround is to have fields like updated_by, created_by, created_at, updated_at in the document being created/updated which are verified using firebase permissions. This is great for documents being inserted or updated, but deleted documents in onWrite cloud functions only have change.before data, and no change.after data, meaning you have no way to see who deleted the document, and at best who updated the document last before deletion.

I am in the middle of trying out some work arounds as follows (but they have serious detractors):

  • Sending an update to a document right before it is to be deleted. Issues -> Might have timing issue, debounce issues, requires messy permissions to ensure that a document is only deleted if it has the proceeding update.
  • Updating it with a field that tags it for deletion and watching for this tag in a cloud function that then does the deleting. Issues -> leads to a very noticeable lag before the item is deleted.

Does anyone have a better way of doing something like this? Thanks!

Richard Cross
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1 Answers1

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  1. Don't delete the document at all. Just add a field called "deleted", set it to true, and add another field with the UID of the user that deleted it. Use these new fields in your queries to decide if you want to deal with deleted documents or not for any given query.

  2. Use a different document in a separate collection that records deletions. Query that collection whenever you need to know if a document has been deleted. Or create a different record in a different database that marks the deletion.

There are really no other options. Either use the existing document or create a new document to record the change. Existing documents are the only things that can be queried - you can't query data that doesn't exist in Firestore.

Renaud Tarnec
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Doug Stevenson
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  • Thanks Doug. I really appreciate the quick response. Both options you outline seem workable and are better than my current attempts at a solution. I'll accept this as the answer. – Richard Cross Dec 19 '21 at 09:40