Rails: how can I add two counter_cache columns in one migration?

Question

I've added forum_threads_count and forum_posts_count columns to the Forums table. The forum_threads_count works just fine. The forum_posts_count has been reset to "0" instead of showing all of the forum posts that have been created before I added the counter cache columns. The relationships are: Forum has_many :forum_threads, ForumThreads has_many :forum_posts, and Forum has_many :forum_posts, through: :forum_threads.

I later found out that I can't use counter_cache with a has_many through: relationship. So I wrote some private methods to add after_create/after_destroy calls to to increment/decrement the counter. The counter works, it's just that it's still not accounting for all of the forum posts that were created before adding these columns to the Forum table. I feel like it's something wrong with how I wrote the migration. Please help and thank you in advance. I appreciate everyone on this site helping people out.

"...add_counters_to_forums_table.rb"(migration file)

class AddCountersToForumsTableAgain < ActiveRecord::Migration

def self.up
 change_table :forums do |t|
   t.integer :forum_threads_count, :forum_posts_count, default: 0
 end

  Forum.reset_column_information

  Forum.all.pluck(:id).each do |id|
   Forum.reset_counters(id, :forum_posts)
   Forum.reset_counters(id, :forum_threads)
  end
end

 def self.down
  change_table :forums do |t|
   t.remove :forum_threads_count, :forum_posts_count
  end
 end

end

models/forum.rb

class Forum < ActiveRecord::Base

 has_many :forum_threads, -> { order ('updated_at DESC') }, dependent: :destroy 

 accepts_nested_attributes_for :forum_threads
 has_many :forum_posts, through: :forum_threads
 accepts_nested_attributes_for :forum_posts

end

models/forum_thread.rb

class ForumThread < ActiveRecord::Base

 belongs_to :user
 belongs_to :forum, counter_cache: true
 has_many :forum_posts, dependent: :destroy
 accepts_nested_attributes_for :forum_posts

end

models/forum_post.rb

class ForumPost < ActiveRecord::Base

 belongs_to :forum_thread, touch: true
 belongs_to :forum 
 belongs_to :user

  after_create :increment_forum_posts_count
  after_destroy :decrement_forum_posts_count

private

 def increment_forum_posts_count
  Forum.increment_counter( 'forum_posts_count', self.forum_thread.forum.id )
 end

 def decrement_forum_posts_count
  Forum.decrement_counter( 'forum_posts_count', self.forum_thread.forum.id )
 end

end

views/forums/index.html.erb

<%= render 'shared/page_title', title: "Forums" %>
<div class="col-md-10 col-md-offset-1">
<div class="actions">
 <%= link_to "Create New Forum", new_forum_path, class: 'btn btn-primary' %>

    <div class="pull-right">
        <%= form_tag @forum_thread, method: :get do |f| %>
            <%= text_field_tag :q, nil, class: 'form-control', placeholder: 'Search...' %>
        <% end %>
    </div>
</div>

 # LIST FORUMS WITH THREADS AND POSTS COUNTER CACHE
<div class="list-group">
    <% @forums.each do |forum| %>
            <a href="<%= forum_forum_threads_path(forum.id, @forum_threads) %>" class="list-group-item">                
                <h3><%= forum.title %>
                    <div class="pull-right small">                  
                        <%= pluralize forum.forum_threads.size, 'thread' %> |                           
                        <%= pluralize forum.forum_posts.size, 'post' %>                         
                    </div>
                </h3>               
        </a>            
    <% end %>
</div>

Answer 1

You can add multiple counter_cache columns to your database, and it looks like you're on the right track as far as naming them. To keep them updated, you'll need to modify your ForumThread and ForumPost models to look a bit like this:

ForumThread < ActiveRecord::Base
  ...
  belongs_to :forum, counter_cache: true
  ...
end

There is more information on counter_cache available on the Rails Guides. There's also a RailsCast about counter_caches,

Answer 2

Your migration looks fine; you could improve it thus:

#db/migrate/add_counters_to_forums_table_....rb
class AddCountersToForumsTable < ActiveRecord::Migration

  def self.up
    change_table :forums do |t|
      t.integer :forum_threads_count, :forum_posts_count, default: 0
    end

    Forum.all.pluck(:id).each do |id|
      Forum.reset_counters(id, :forum_posts_count)
      Forum.reset_counters(id, :forum_threads_count)
    end
  end

  def self.down
    change_table :forums do |t|
      t.remove :forum_threads_count, :forum_posts_count
    end
  end

end

Good reference: "Adding a Counter Cache to Existing Records"

---

Because the counter_cache is defined on the association, as long as you have it attached to different associations, you can have as many as you wish:

#app/models/forum.rb
class Forum < ActiveRecord::Base
  has_many :forum_threads
  has_many :forum_posts
end

#app/models/forum_thread.rb
class ForumThread < ActiveRecord::Base
  belongs_to :forum, counter_cache: true
end

#app/models/forum_post.rb
class ForumPost < ActiveRecord::Base
  belongs_to :forum, counter_cache: true
end

---

Update

I think the issue is that you're using counter_cache on a has_many :through association:

#app/models/forum.rb
class Forum < ActiveRecord::Base
  has_many :forum_threads
  has_many :forum_posts, through: :forum_threads

  delegate :forum_posts_count, to: :forum_threads
end

#app/models/forum_thread.rb
class ForumThread < ActiveRecord::Base
  belongs_to :forum
  has_many :forum_posts
end

#app/models/forum_post.rb
class ForumPost < ActiveRecord::Base
  belongs_to :forum_thread, counter_cache: true
end

Here is a good reference: counter_cache with has_many :through

---

If you used my code above (for has_many :through), you'll be best going into the Rails console and update the various ForumThreads as follows:

$ rails c
$ forums = Forum.all
$ forums.each do |forum|
$  forum.forum_posts.pluck(:id).each do |id|
$    ForumPost.reset_counters(id, :forum_posts_count)
$  end
$ end

This should reset the counters properly for you.

---

Update

In regard your question, I still feel you can make the counter_cache work with the has_many :through. I read up on this tutorial (counter_cache with has_many :through), and seems to confirm that you can put the counter_cache in the join model.

Although we aren't doing this per se, I see no reason why it would not work.

In your ForumPost, you really don't need belongs_to :forum -- that should only be applicable for the ForumTopic.