title: Query fields dynamically in MongoDB
body: <p>Let's say the schema is: </p>
  
  <pre><code>var Rows = mongoose.model('Rows', {   
      row1: String,
      row2: String
  });
  </code></pre>
  
  <p>How would I query one of the rows at random? For example:</p>
  
  <pre><code>var rand = Math.floor(Math.rand() * 2);
  Rows.find({ "row" + rand: "sup" }, function (err, result) {
      if (err) {
          console.log(err);
      }
      console.log(result);
  });
  </code></pre>
  
  <p>This code get's an error <code>SyntaxError: Unexpected token +</code></p>