Querying by a field with type 'reference' in Firestore

Question

I have a collection called 'categories' containing a single document with ID: 5gF5FqRPvdroRF8isOwd.

I have another collection called 'tickets'. Each ticket has a reference field which assigns the ticket to a particular category.

The field in the tickets collection is called 'category' and has a field type of reference.

In the code below, categoryDocId is the document ID of the category I want to query by.

const categoryDocID = `5gF5FqRPvdroRF8isOwd`;

const files = await firebase
  .firestore()
  .collection('tickets')
  .where('category', '==', categoryDocID)
  .get();

Why does files.length return 0?

For testing, I changed the category field type to string, and set it to the category ID instead of a direct reference. This correctly returned tickets assigned to the category, which leads me to believe it's something about how I'm querying a reference field.

Answer 1

As you will read here in the doc, the Reference Data Type is used to store DocumentReferences.

If you want to use it in a query, you cannot use a simple string, neither the UID of the document (i.e. '5gF5FqRPvdroRF8isOwd'), nor the string value that is stored in the field (i.e. '/categories/5gF5FqRPvdroRF8isOwd').

You have to build a DocumentReference and use it in your query, as follows:

const categoryDocRef = firebase.firestore()
   .collection('categories')
   .doc('5gF5FqRPvdroRF8isOwd');

const files = await firebase
  .firestore()
  .collection('tickets')
  .where('category', '==', categoryDocRef)
  .get();

Answer 2

With Firebase Version 9 (Dec, 2021 Update):

You must make a document reference with "categories/5gF5FqRPvdroRF8isOwdand" then use it in your query:

import { doc, query, collection, where, getDocs } from "firebase/firestore";

const categoryDocRef = doc(db, "5gF5FqRPvdroRF8isOwd");

const q = query(
  collection(db, "tickets"),
  where("category", "==", categoryDocRef)
);

const ticketDocsSnap = await getDocs(q);

Answer 3

Here is how I use reference type to query a collection (node.js + typescript):

let myCollectionADocument = await admin.firestore().collection("collection_a").doc("documentId").get();
let myCollectionB = await admin.firestore().collection("collection_b").where("collection_a_id", "==", myCollectionADocument.ref).get();