title: How to do a bulk update in Firestore
body: <p>I'm using Cloud Firestore and have a collection of documents. For each document in the collection I would like to update one of the fields. </p>
  
  <p>Using a transaction to perform the update would be inefficient because I do not need to read any of the data while updating it. </p>
  
  <p>Batch updates seem like the right direction, however the docs do not include examples of updating multiple docs at once. See here: <a href="https://firebase.google.com/docs/firestore/manage-data/transactions" rel="noreferrer">Batched Writes</a></p>