title: Problems exporting model functions with Mongoose
body: <p>I'm struggling with creating model functions for Mongoose models. I define a method here:</p>
  
  <pre><code>Schema.listingSchema.method('applyPrice', function() {
    this.price = priceFromString(this.title);
  });
  </code></pre>
  
  <p>and I access it here:</p>
  
  <pre><code>var listing = new Listing();
  
  // assign all relevant data
  listing.title = title;
  ...
  
  // pull the price out of the title and description
  listing.applyPrice(listing);
  </code></pre>
  
  <p>where</p>
  
  <pre><code>Listing = mongoose.model('Listing', Schema.listingSchema);
  </code></pre>
  
  <p>and I receive the error:</p>
  
  <pre><code>TypeError: Object #&lt;model&gt; has no method 'applyPrice'
  </code></pre>
  
  <p>Can anyone see the issue?</p>