Firestore cursor methods not working with document snapshots

[myandrienko]

• Firebase SDK version: 5.5.0
• Firebase Product: firestore

I'm using Firebase Admin SDK in Firebase Cloud Functions environment. I noticed that firebase.firestore.Query cursor methods, such as startAt, startAfter etc, are not working correctly when called with DocumentSnapshot as argument.

Collection test is populated with the following documents:

a: { v: "a", sort: 1 }
b: { v: "b", sort: 0 }
c: { v: "c", sort: 2 }

Here's my cloud function code:

const db = admin.firestore();
const coll = db.collection('test');
const query = coll.orderBy('sort');

return coll
 .doc('a')
 .get()
 .then((snap) =>
 query
 .startAt(snap)
 .get()
 )
 .then((snaps) => {
 console.log(snaps.size);
 });

Expected behavior to receive two documents (a and c), instead the following exception is thrown:

Error: Cannot encode type ([object Object]) to a Firestore Value
 at Function.encodeValue (/user_code/node_modules/firebase-admin/node_modules/@google-cloud/firestore/src/document.js:669:11)
 at Query._buildPosition (/user_code/node_modules/firebase-admin/node_modules/@google-cloud/firestore/src/reference.js:1267:44)
 at Query.startAt (/user_code/node_modules/firebase-admin/node_modules/@google-cloud/firestore/src/reference.js:1295:28)
 at coll.doc.get.then (/user_code/index.js:20:8)
 at process._tickDomainCallback (internal/process/next_tick.js:135:7)

[google-oss-bot]

Hey there! I couldn't figure out what this issue is about, so I've labeled it for a human to triage. Hang tight.

[google-oss-bot]

Hmmm this issue does not seem to follow the issue template. Make sure you provide all the required information.

[myandrienko]

BTW, similar code works fine with Firebase Javascript SDK:

<script src="https://www.gstatic.com/firebasejs/4.6.2/firebase.js"></script>
<script src="https://www.gstatic.com/firebasejs/4.6.2/firebase-firestore.js"></script>
<script>
 firebase.initializeApp(/* ... */);

 const db = firebase.firestore();
 const coll = db.collection('test');
 const query = coll.orderBy('sort');

 coll
 .doc('a')
 .get()
 .then((snap) =>
 query
 .startAt(snap)
 .get()
 )
 .then((snaps) => {
 console.log(snaps.size);
 });
</script>

Output:

> 2

[myandrienko]

Oh, I found a note in documentation saying that these methods are not supported Node.js client. I'm now closing this issue.

A viable replacement for me is offset method. I think documentation for Firestore Node.js client should be linked from Firebase documentation to avoid confusion :)