using last after model included doesnt work - mysql

Question

Im stuck (still very new to Rails), and cant figure out why its not working:
I have:
class Message < ActiveRecord::Base
attr_accessible :updated_at
has_many :categories_messages
has_many :categories, through: :categories_messages
end
class CategoriesMessage < ActiveRecord::Base
attr_accessible :category_id, :message_id
belongs_to :category
belongs_to :message
end
class Category < ActiveRecord::Base
attr_accessible :name
has_many :categories_messages
has_many :message, through: :categories_messages
end
#messagesPer = Category.all.includes(:messages).group('categories.id').order("COUNT(messages.id) DESC")
<% #messagesPer.each_with_index do |message, i| %>
<tr>
<td><%= i+1 %></td>
<td><%= message.name %></td>
<% if message.categories_messages.exists? %>
<td><%= message.messages.last.updated_at.to_s.to_date %></td>
<td><%= message.messages.first.updated_at.to_s.to_date %></td>
<td><%= message.messages.count %></td>
<% else %>
<td>0</td>
<td>0</td>
<% end %>
</tr>
<% end %>
So i want it to show :
the name of Category, date the last message was created , date first message was created, and all messages in that category.
ALl works fine, apart from the fact that it only shows the date when the first message was created, but never the last (still shows first date on the last).
What am i doing wrong?
UPDATE:
if i put
#messagesPer = Category.all.includes(:messages).group('categories.id')
it does show the right date for last and first messages but as soon as i add order it breaks...

Answer 1

I might be helpful to include the error information you get after adding an order clause to the query.
However, I can spot some odd things in the code. The CategoriesMessage model seems to be there simply to satisfy the condition that a category can have many messages and vice versa. You don't need a model for this many-to-many relationship though, Rails will handle this automatically for you.
Your models should be looking like this:
class Message < ActiveRecord::Base
attr_accessible :updated_at
has_and_belongs_to_many :categories
end
class Category < ActiveRecord::Base
attr_accessible :name
has_and_belongs_to_many :messages
end
And in your database you have these tables: messages, categories,categories_messages, where the last one is the join table which only contains columns for amessage_idand acategory_id`.
Then you can simply do something like this in your code:
category.messages.each { |message| puts message.updated_at }
Also see this Ruby on Rails tutorial article for more information. If this doesn't work for you, please post the exact error you get.