title: Calling custom method from mongoose schema
body: <p>I made custom methods with two ways, But not working.  </p>
  
  <p>models</p>
  
  <pre><code>...
  // I read it from other stack overflow QA
  categorySchema.methods.postChange = function(){
  console.log('postChange');
  };
  
  // Mongoose reference doc
  categorySchema.methods('postChange', function(){
  console.log('postChange');
  });
  
  var Category = mongoose.model('category',categorySchema);
  
  module.exports = Category;
  </code></pre>
  
  <p>routes</p>
  
  <pre><code>...
  router.post('/update_cat', upload.single('image_file'), function(req, res){
  Category.findOneAndUpdate({name: req.body.name}, {href: req.body.href}, function(err, doc){
      doc.href = req.body.href;
      Category.postChange();
      (err)?res.json(err):res.redirect('./reg_line');
      });
  });
  </code></pre>
  
  <p>and The error is 'Category.postChange is not a function'.</p>