title: How to use WHERE clause in mongodb when the key of a field is numeric
body: <p>Say I insert a document into mongo like below:</p>
  
  <pre><code>db.test.insert({1 : { 2 : "some value"}, 3 : { 4 :"some other value"}});
  </code></pre>
  
  <p>How do I use the $where clause to match this document? I tried using the following:</p>
  
  <pre><code>db.test.find({"$where" : "this.1.2 == this.3.4"});
  </code></pre>
  
  <p>but I ended up getting this error message.</p>
  
  <pre><code>    error: {
      "$err" : "JavaScript execution failed: SyntaxError: Unexpected number",
      "code" : 16722
      }
  </code></pre>
  
  <p>I know $where is not recommended, but say if I have to use it, is there any way to accomplish this? Thanks in advance.</p>