CollectionReference 到 DocumentReference

Question

I'm trying to perform a firestore transaction in Flutter. Therefore I need to pass the documentReference .

There is no problem, when accessing the "lesson" document based on the identifier. The issue is when fetching the active user pass. The where I'm trying to use returns the Query , and the .reference() returns the CollectionReference (which is not accepted by the transaction method).

How can I get the reference to the document basing on the value of its field.

To spice it up: DB rules don't allow me to read ALL the passes. I've got only access to those, that have my UserID (double checked - working).

  DocumentReference lessonRef =
    await _db.collection('lessons').document(lesson.identifier);

  CollectionReference passRef = await _db
        .collection('passes')
        .where('userID', isEqualTo: user.identifier).reference();

Answer 1

You can get the DocumentReference of the Queried documents like so:

Firestore.instance
.collection('passes')
.where('userID', isEqualTo: user.identifier)
.snapshots()
.listen((reference) =>
    data.documents.forEach((doc) => /*do what you want with doc.reference*/));

(I'm not an expert in Flutter and I could't test the code, but I based the answer in the API reference )