title: save method in Mongoose failed
body: <p>I tried to use <code>save()</code> in Mongoose but saw empty collection been inserted.</p>
  
  <p>my photo schema is like this :</p>
  
  <pre><code>var mongoose = require('mongoose');
  var Schema = mongoose.Schema;
  
  var photosSchema = mongoose.Schema({
      photos: {
          type: String
      },
      caption: {
          type: String
      }
  });
  
  var Photos = module.exports = mongoose.model('photos', photosSchema);
  
  module.exports.getAllPhotos = function(callback){
      Photos.findAll(callback);
  }
  </code></pre>
  
  <p>and in my route I do </p>
  
  <pre><code>var Photo = require('../models/photos');
  router.post('/upload_photo', upload.any(), function(req, res, next) {
      var photo = new Photo();
      var data = {
          photos:'abc.jpg',
          caption:'something..'
      }
      photo.save(data);
      res.end();
  });
  </code></pre>
  
  <p>Am I using <code>save</code> wrong here? I know I can define a method like savePhoto and export it, but how to use <code>save()</code> directly instead?</p>