title: Firestore: request for a list of collection IDs
body: <p>[Firestore documentation says:][1]</p>
  <blockquote>
  <p>###Queries other than document reads
  For queries other than document reads, such as a request for a list of collection IDs, you are billed
  for one document read. If fetching the complete set of results
  requires more than one request (for example, if you are using
  pagination), you are billed once per request.</p>
  </blockquote>
  <p>I cannot find any information of how to perform such queries to get only IDs.</p>
  <p>Does anyone know how?
  [1]: <a href="https://firebase.google.com/docs/firestore/pricing#operations" rel="nofollow noreferrer">https://firebase.google.com/docs/firestore/pricing#operations</a></p>