title: mongodb Modified field name may not start with $
body: <p>I manage my db with mongodb using node.js</p>
  
  <p>In server.js, this code evoke error</p>
  
  <pre><code>TB_LolCombinationOfChampion.update({},{ $set: { $set: { win: 23445123123 }}},{multi: true},function (err, raw) {
                          if (err) console.log(err);
                          console.log('The raw response from Mongo was ', raw);
                          });
  </code></pre>
  
  <p>I get this error</p>
  
  <blockquote>
    <p>{ [MongoError: Modified field name may not start with $]   <br>name:
    'MongoError',   <br>err: 'Modified field name may not start with $',<br>
    code: 15896,   <br>n: 0,   <br>connectionId: 601,   <br>ok: 1 } 
    <br>The raw response
    from Mongo was  null</p>
  </blockquote>
  
  <p>Why this error evoke and how I avoid this error?</p>