Query firestore database for document id

Try this:

db.collection('books').doc('fK3ddutEpD2qQqRMXNW5').get()

(The first query is looking for an explicit user-set field called 'id', which probably isn't what you want.)

I am a bit late, but there is actually a way to do this

db.collection('books').where(firebase.firestore.FieldPath.documentId(), '==', 'fK3ddutEpD2qQqRMXNW5').get()

This might be useful when you're dealing with firebase security rules and only want to query for the records you're allowed to access.

June, 2021

The new v9 modular sdk is tree-shakeable and results in smaller compiled apps. It is recommended for all new Firestore apps.

import { doc, getDoc } from "firebase/firestore";

const snap = await getDoc(doc(db, 'books', 'fK3ddutEpD2qQqRMXNW5'))

if (snap.exists()) {
  console.log(snap.data())
}
else {
  console.log("No such document")
}

This is based on the example from the firestore docs

import { doc, getDoc } from "firebase/firestore";

const docRef = doc(db, "cities", "SF");
const docSnap = await getDoc(docRef);

if (docSnap.exists()) {
  console.log("Document data:", docSnap.data());
}
else {
  // doc.data() will be undefined in this case
  console.log("No such document!");
}

You could make this into a helper function

async function getDocument (coll, id) {
  const snap = await getDoc(doc(db, coll, id))
  if (snap.exists())
    return snap.data()
  else
    return Promise.reject(Error(`No such document: ${coll}.${id}`))
}

getDocument("books", "fK3ddutEpD2qQqRMXNW5")

You can use the __name__ key word to use your document ID in a query.

Instead of this db.collection('books').doc('fK3ddutEpD2qQqRMXNW5').get() you can write

db.collection('books').where('__name__', '==' ,'fK3ddutEpD2qQqRMXNW5').get().

In this case you should get an array of length 1 back.

The firebase docs mention this feature in the rules documentation. https://firebase.google.com/docs/reference/rules/rules.firestore.Resource