如何从控制器动作中向Rails动态添加after过滤器？

Question

Each time a user accesses a page in my Rails app, the database needs to send them a Thingy. When the database runs out of Thingies, it has to do some expensive processing to generate more. I want to add a controller filter dynamically to generate the thingies after the response has been sent to the user so that it doesn't affect page load times. Here's what my controller looks like:

class ThingyController < ApplicationController

  def get_a_thingy
    if Thingy.count <= 5 
      # Only five thingies left! we need to generate some more. 
      # I want to dynamically send a block to an after_filter: here to  
      # generate thingies after the controller sends the response  
      # because generating thingies is really slow
    end

    # Pop the first thingy from the database and return
    thingy = Thingy.first
    thingy.delete 
    return thingy.content
  end

What can I add in the get_a_thingy function to make this happen?

Answer 1

You may try some background processing tools( https://www.ruby-toolbox.com/categories/Background_Jobs check this), cause I'm not sure you can do it inside a request handler.

You may also try to return all the content to user (via smthing like http streaming) and only then make your heavy things.

Answer 2

Probably the best idea will by a gem like delayed_job there is also a railscast for it.

Delayed job is an asynchronously priority queue system.

• Install and setup the delayed_job. It is pretty well documented on the github page .

• Start the worker with rake jobs:work

• Now simply change your code to use the delay job by adding the .delay method

class ThingyController < ApplicationController
  after_filter :generate_thingies
  .
  .
  .
  def generate_thingies
    if Thingy.count <= 5
      #change
      Thingy.generate_thingies
      #to
      Thingy.delay.generate_thingies
    end
  end
end

NOTE: This is a small tutorial and I left out a some of things that you will need to get it working. I recommend you to check the Github page for a full documentation.

Answer 3

Just put the if statement that checks for the number of thingies in your after_filter code:

class ThingyController < ApplicationController
  after_filter :generate_new_thingies

  def get_a_thingy
    thingy = Thingy.first
    thingy.delete
    return thingy.content
  end

  def generate_new_thingies
    if Thingy.count <= 5
      # Generate thingies
    end
  end
end

Does using after_filter really prevent long page loads? It may be better to have a look at something like Delayed Job or Whenever .