查找孤立的子集合文档

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 is possible to get the access to these documents. Save IDs somewhere when users delete the documents. Or just find out the document ID in console.firebase.google.com. If you have ID of removed doc you will able to fetch the subcollection's docs. The removed doc ID marked italic in Firebase Console ( like this one ).

Answer 2

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.

Answer 3

Adding a cloud function to delete subcollections when a doc is deleted, can help with this problem from occurring again. https://firebase.google.com/docs/firestore/solutions/delete-collections#cloud_function

exports.removeSubCollections = functions.firestore
.document("col1/{docId}")
.onWrite(async (change, context) => {
  const docId = context.params.docId;

  if(!change.after.exists) {
    //Delete all subcollections here
  }
});