Firestore: Query by item in array of document

See Henry's answer, as we've no made Array Contains queries available.

Unfortunately not yet, although it's on our roadmap.

In the meantime, you'll need to use a map instead, in the form of:

photos: {
    id1: true
    id2: true
}

Now you can find all users with id1 by filtering by photos.id1 == true.

Read more about querying such sets in the Firebase documentation.

Added 'array-contains' query operator for use with .where() to find documents where an array field contains a specific element.

https://firebase.google.com/support/release-notes/js 5.3.0

Update: also available in @google-cloud/firestore: https://github.com/googleapis/nodejs-firestore/releases/tag/v0.16.0

Update 2 https://firebase.googleblog.com/2018/08/better-arrays-in-cloud-firestore.html

Update 3 now available in Admin Node.js SDK v6.0.0 https://github.com/firebase/firebase-admin-node/releases