Firestore delete document and all documents referencing it

Question

this question is regarding Firebase (+ Flutter)

is it possible to delete a document and all documents referencing it?

Lets assume i have a structure like this:

-users (collection)
  - name
  - bookmarks ((sub)collection)
    - postId
-post (collection)
  - userId
  - name
  - ...

Now if i delete a post, i want to delete all bookmarks referencing that post. (From all users). Is there an automatic way (coming from RDBMS).

Another question: How can i query all posts and "join" the user infos.

Something like this:

return firestore
        .collection("posts")
        .orderBy("createdAt")
        .snapshots(); // I want to join the userInformation

And are these nested queries then and counting to the api limit?

Thanks in advance

blaneyneil blaneyneil · Accepted Answer · 2018-08-28T05:18:01

you have to query the docs and then batch delete them. i don't use subcollections, and i'm not going to look up how to query them, but with a root level schema you'd delete the post with a standard firestore delete, referencing the documentID. assuming the documentID is the same as your 'postID' field (and if it isn't, refactor your schema) you'd then:

final WriteBatch _batch = Firestore.instance.batch();

  QuerySnapshot _query = await dbUsers.where('postId', isEqualTo: thatDocumentID).getDocuments();

  _query.documents.forEach((doc) {
    _batch.delete(dbUsers.document(doc.documentID));
  });

  await _batch.commit();

be aware that batches can only be done 500 at a time:

https://firebase.google.com/docs/firestore/manage-data/transactions

so you'd have to split up your _batch.commit() calls as necessary.

Firestore delete document and all documents referencing it

2 Answers