title: Cloud Firestore Update
body: <p>I'd like update document in cloud firestore according to value in document. Something like this. I have few documents with random names and values and one document with values  <code>id = 1</code> , <code>name = patryk</code> . And now I'd to update document with <code>name=patryk</code>. And I don't know document name because I make them like this and they have a random name.</p>
  
  <pre><code>b.collection("Users")
      .add(postMapa)
      .addOnCompleteListener
  </code></pre>
  
  <p>How to do this? <a href="https://firebase.google.com/docs/firestore/manage-data/add-data" rel="nofollow noreferrer">here</a> I need have the name of the document but I don't have.</p>