title: Only search mongoose model for keys in schema
body: <p>I'm building a search to filter results from a mongoose model. All the filter options except for two need to queried into Model1. The other two will query those results in Model2.</p>
  
  <p>Before I added these last two options, I had the search working like so:</p>
  
  <pre><code>var filterOptions = req.body;
      for(var key in filterOptions) {
      if(filterOptions.hasOwnProperty(key)) {
          filterOptions[key] = new RegExp(filterOptions[key], "i");
      }
  }
  
  Model1.find(filterOptions, function(err, results) {
      //Use the results to search Model2.
  })
  </code></pre>
  
  <p>I'm getting stuck how can I specify to only query Model1 with keys that are in that model. (Or, if there's a way to edit the filterOptions object to not include the last two options.) Thanks.</p>