How to use VueUse useFirestore() with a Where QueryConstraint?

Question

I have a Firestore users doc that looks something like this:

{
    currentCompanyId: "123",
    displayName: "Mary Jane" 
}

And a Firestore websites doc that looks something like this:

{
    companyId: "123",
    homePageUrl: "https://www.google.com/"
}

Now I'm trying to use the VueUse useFirestore() wrapper to display the websites doc.

To do that I am referencing the currentCompanyId property of the users doc inside a where Query Constraint like so:

<template>
  <div>
    {{ websites?.[0] }}
  </div>
</template>

<script setup lang="ts">
import { useAuth } from '@vueuse/firebase/useAuth';
import { useFirestore } from '@vueuse/firebase/useFirestore';
import { collection, doc, query, where } from 'firebase/firestore';
import { auth, db } from 'src/config/firebase';
import { User } from 'src/types';
import { computed } from 'vue';

const { user: authUser } = useAuth(auth);
const userDocRef = doc(db, `users/${authUser.value?.uid}`);
const user = useFirestore<User>(userDocRef);

const websiteQuery = computed(() =>
  query(
    collection(db, 'websites'),
    where('companyId', '==', user.value?.currentCompanyId) // This produces an error
    // where('companyId', '==', '123') // This works, but is not practical
  )
);
const websites = useFirestore(websiteQuery);
</script>

Hard-coding the companyId value of 123 works.

But whenever I use user.value?.currentCompanyId inside the computed ref it throws an error saying this:

TypeError: right-hand side of 'in' should be an object, got null

Answer 1

I figured it out.

The problem was that user.value?.currentCompanyId is initially null.

Here is the error message again:

TypeError: right-hand side of 'in' should be an object, got null

It's basically saying the right-hand side of the Where query constraint should be an object, but it got null.

Wrapping the query in a computed ref will eventually change the value from null into something else when it updates. But initially it is null. And that is the cause of the error.

To overcome this problem you can set some initial properties of user in the useFirestore. So the Where query constraint will use that non-null value initially. Even an empty string will be ok. You can use anything that is not null.

Here is the full code:

<template>
  <div>
    {{ websites?.[0] }}
  </div>
</template>

<script setup lang="ts">
import { useAuth } from '@vueuse/firebase/useAuth';
import { useFirestore } from '@vueuse/firebase/useFirestore';
import { collection, doc, query, where } from 'firebase/firestore';
import { auth, db } from 'src/config/firebase';
import { User } from 'src/types';
import { computed } from 'vue';

const { user: authUser } = useAuth(auth);
const userDocRef = doc(db, `users/${authUser.value?.uid}`);
const user = useFirestore<User>(userDocRef, { currentCompanyId: '' }); // <-- See change here

const websiteQuery = computed(() =>
  query(
    collection(db, 'websites'),
    where('companyId', '==', user.value?.currentCompanyId)
  )
);
const websites = useFirestore(websiteQuery);
</script>