Find orphaned subcollection documents

Question

The firestore docs say:

When you delete a document that has associated subcollections, the subcollections are not deleted. They are still accessible by reference. For example, there may be a document referenced by db.collection('coll').doc('doc').collection('subcoll').doc('subdoc') even though the document referenced by db.collection('coll').doc('doc') no longer exists.

Is there any way to access these documents if you lose the reference do db.collection('coll').doc('doc')? Say for example client A goes offline, and then creates coll/doc/subcoll/foo. Then the server deletes coll/doc and it's subcollections. Later client A comes back online and syncs foo. It appears that now there's now way for me to know that foo exists and is wasting space in the database.

Answer 1

It should be possible to retrieve all documents of the sub-collection (including orphans) with .collectionGroup('subcoll').

Then you can iterate over them with .forEach() and retrieve their parent with .getParent().

If they don't have a parent, they are an orphan and you can delete them.