Use model callback

Bad Smell

<% form_for @post do |f| %>
  <%= f.text_field :content %>
  <%= check_box_tag 'auto_tagging' %>
<% end %>

class PostsController < ApplicationController
  def create
    @post = Post.new(params[:post])

    if params[:auto_tagging] == '1'
      @post.tags = AsiaSearch.generate_tags(@post.content)
    else
      @post.tags = ""
    end

    @post.save
  end
end

In this example, if user clicks the checkbox auto_tagging, we will generate tags according to the content of post, then assign the tags to the post before saving the post. We can move the tags assignment codes into the model by using model callback.

Refactor

class Post < ActiveRecord::Base
  attr_accessor :auto_tagging
  before_save :generate_tagging

  private
  def generate_taggings
    return unless auto_tagging == '1'
    self.tags = Asia.search(self.content)
  end
end

<% form_for @post do |f| %>
  <%= f.text_field :content %>
  <%= f.check_box :auto_tagging %>
<% end %>

class PostsController < ApplicationController
  def create
    @post = Post.new(params[:post])
    @post.save
  end
end

As you see, we create a before_save callback generate_tagging in Post model, it generates and assigns tags if user clicks the auto_tagging checkbox. Then PostsController has no needs to take care of the model logic.