Rails how to update a column after saving?

问题:

I want to create an after_save method for my rate action. It would divide rating_score/ratings and update the column rating.

class KonkurrancersController < ApplicationController
  def rate
    @konkurrancer = Konkurrancer.find(params[:id])
    @container = "Konkurrancer"[e-mail]_s

    @konkurrancer.rating_score += params[:vind][:rating].to_i
    @konkurrancer.ratings += 1
    @konkurrancer.save

    respond_to do |format|
      format.js
    end
  end
end

This is my model:

class Konkurrancer < ActiveRecord::Base
  after_save :do_foobar

  private
    def do_foobar

      rating_score = self.rating_score
      ratings = self.ratings
      rating = (rating_score/ratings)
      self.update_attributes(:rating => rating)

    end
end

My rails log:

Started POST "/konkurrancers/rate/46" for 127.0.0.1 at 2011-04-26 23:40:56 +0200

  Processing by KonkurrancersController#rate as */*
  Parameters: {"utf8"=>"Ô£ô", "authenticity_token"=>"MACFM37hX4S6XA9vryn7gtfl21P
vcaPBSiKDI8mfurg=", "vind"=>{"rating"=>"4"}, "id"=>"46"}
  ←[1m←[36mKonkurrancer Load (1.0ms)←[0m  ←[1mSELECT `konkurrancers`.* FROM `kon
kurrancers`←[0m
  ←[1m←[35mCACHE (0.0ms)←[0m  SELECT `konkurrancers`.* FROM `konkurrancers`
  ←[1m←[36mCACHE (0.0ms)←[0m  ←[1mSELECT `konkurrancers`.* FROM `konkurrancers`←
[0m
  ←[1m←[35mKonkurrancer Load (1.0ms)←[0m  SELECT `konkurrancers`.* FROM `konkurr
ancers` WHERE (`konkurrancers`.`cached_slug` = '46') LIMIT 1
  ←[1m←[36mSQL (2.0ms)←[0m  ←[1mSELECT sluggable_id FROM slugs WHERE ((slugs.slu
ggable_type = 'Konkurrancer' AND slugs.name = '46' AND slugs.sequence = 1))←[0m
  ←[1m←[35mKonkurrancer Load (1.0ms)←[0m  SELECT `konkurrancers`.* FROM `konkurr
ancers` WHERE (`konkurrancers`.`id` = 46) LIMIT 1
  ←[1m←[36mSQL (0.0ms)←[0m  ←[1mBEGIN←[0m
  ←[1m←[35mLink Load (1.0ms)←[0m  SELECT `links`.* FROM `links` WHERE (`links`.k
onkurrancer_id = 46) LIMIT 1
  ←[1m←[36mSQL (0.0ms)←[0m  ←[1mROLLBACK←[0m
Rendered konkurrancers/_rating.html.erb (1.0ms)
Rendered konkurrancers/rate.js.erb (22.0ms)
Completed 200 OK in 606ms (Views: 286.0ms | ActiveRecord: 6.0ms)

How should I create this?

回答1:

what you want is a callback. You can create an after_save callback on your Konkurrancer model, which triggers after the save() method is called for that model.

For example:

class Konkurrancer < ActiveRecord::Base
  after_save :do_foobar

  private
    def do_foobar

      rating_score = self.rating_score
      ratings = self.ratings
      rating = (rating_score/ratings)
      self.update_attributes(:ratings => rating)

    end
end

[EDIT] You should use self, since the model you are editing is the model itself. Test it out, and apply necessary logic/implementation.

Have a look at this guide for more info.

Hope that helps!

回答2:

Any update_attribute in an after_save callback will cause recursion, in Rails3+. What should be done is:

after_save :updater
# Awesome Ruby code
# ...
# ...

private

  def updater
    self.update_column(:column_name, new_value) # This will skip validation gracefully.
  end

回答3:

Not sure why people are upvoting the wrong answer and downvoting the correct answer.

Zakelfassi is right and Christian Fazzini is wrong for Rails 3 and above. If you do #update_attributes in a save callback you go into an endless recursion. You want to do #update_column as per his example.

Try it for yourself and you'll see.

回答4:

  @konkurrancer.update_attributes :ratings=>'updated value'

回答5:

see this after_save method