title: Search and update single document from firestore collection
body: <p>I want to search single document in Firestore with specific query. Then update record if found. And equivalent to <code>where</code> on collection but on a doc.</p>
  
  <pre><code>const usersRef = Firebase.firestore()
        .collection("users")
        .doc(currentUser.uid);
  
        usersRef.get().then(user =&gt; {
         // get record where user.dayData.date == Date.now() or something
  
        }).then(() =&gt; // update record)
  
  </code></pre>
  
  <p>// db datastructure is like this. Will like to update totalhours for specific dates</p>
  
  <pre><code>        projectData: {
              dayData: [
                  { date: 1564656952780, totalHours: 15 },
                  { date: 1568659952780, totalHours: 65 },
                  { date: 1563659952780, totalHours: 15 },
                  { date: 1564651234567, totalHours: 5 }
              ],
              userData: { displayName: "Ajiboye John" }
          }
      },
  
  </code></pre>