title: angular/express api/mongodb update issue
body: <p>working with a full MEAN stack. 
  trying to write data to a "notes" array in my mongodb document id #1.</p>
  
  <p>mongo document:</p>
  
  <pre><code>&gt; db.contacts.find().pretty()
  {
  "_id" : ObjectId("5a294af85e96746421bf35f1"),
  "id" : 1,
  "type" : "dealer",
  "name" : "ken yoder",
  "company" : "kens sales",
  "phone" : "817-403-9767",
  "notes" : [
      {
          "date" : "Thu Dec 07 2017 08:15:37 GMT-0600 (CST)",
          "by" : "@me",
          "note" : "this is a note"
      },
      {
          "date" : "Thu Dec 07 2017 08:16:31 GMT-0600 (CST)",
          "by" : "@donny",
          "note" : "bla bla bla mumford and sons"
      },
      {
          "date" : "Thu Dec 07 2017 08:34:03 GMT-0600 (CST)",
          "by" : "@ken",
          "note" : "test with another note"
      },
      {
          "date" : "Thu Dec 07 2017 08:34:29 GMT-0600 (CST)",
          "by" : "@ken",
          "note" : "test with another notey note note"
      }
  ],
  "setNotes" : {
      "date" : "Thu Dec 07 2017 10:52:09 GMT-0600 (CST)",
      "by" : "@kale",
      "note" : "hhsdihufiudhsiuhdshuifds"
  }
  }
  </code></pre>
  
  <p>express code:</p>
  
  <pre><code>app.get('/newNote/:noteFor/:noteCount/:noteBy/:note/', function (req, res) {
          var setNotes = "notes."+req.params.noteCount;
          db.collection('contacts').update({ id:req.params.noteFor }, { $set: { setNotes : {date: Date(), by: req.params.noteBy, note: req.params.note} }}, function(err, res) {
                  if (err) throw err;
                  console.log("notefor: "+req.params.noteFor+" noteCount: "+setNotes+" noteBy: "+req.params.noteBy+" note: "+req.params.note);
                  console.log(res.result.nModified + " for " + req.params.noteFor + " updated");
          });
  });
  </code></pre>
  
  <p>if i run this code as it sits, i get nothing, no insert, no errors. 
  - if i change the update id from "req.params.id" to "1", i get an insert but...
  - instead of using my "setNotes" variable (which outputs "notes.4") for the $set identifier, it created a new object called "setNotes".</p>
  
  <pre><code>API URL: /newNote/1/4/@kale/this is a note test
  </code></pre>