Rails - Apr 2006 - Order By Number of Comments

Hi,

I am new to Ruby on Rails, so I apologise if this has been answered 
elsewhere.  I have had a look through the list but I can''t seem to find
what I am trying to do.

I have implemented the standard blog and comments app from the 
screencast.  However I am trying to extend the functionality.

I want to be able to display a list of posts and order them by the total 
number of comments they have.  It will act as a most discussed view.

This is what I have been trying in the controller, with no luck :

def show_discussed
  @contents.find(:all, :order => "contents.comment.size DESC",
:joins =>
"comments")
end

I have got some SQL that works : (I renamed posts to contents)

select contents.*, count(*) as comment_total from contents, comments 
WHERE contents.id = comments.content_id group by contents.id;

But this does not return the posts with no comments.

I would really appreciate any help.

Thank you in advance.

Hamza

-- 
Posted via http://www.ruby-forum.com/.

> Date: Mon, 3 Apr 2006 16:36:15 +0200
> From: Hamza <hamzakc@gmail.com>
> def show_discussed
>   @contents.find(:all, :order => "contents.comment.size DESC",
:joins =>
> "comments")
> end
As Francois pointed me to, you want sort_by. find returns an array, and 
array mixes in Enumerable.

http://www.ruby-doc.org/core/classes/Enumerable.html#M002092

So something like this:

@contents.find(:all)
@contents.sort_by(|x| f(x))

Where f(x) is code that evaluates the number you want to sort on, like 
the number of comments... Comment.count(:conditions => "content_id =
?",
x.id)

Chris S

One other thing you could do is add an auto-populating field to the
parent in the relationship. So, say I have a post model, which has_many
:comments. Using a magic field of comments_count, this will be
auto-updated when comments are added or removed from the post. So, I
could get the list in the order you want, by simply doing...

.find(:all, :order_by => ''comments_count DESC'', :conditions
=>
[''comments_count > x''])

And then I can forget about joins etc... Handy magic field name! (Saves
doing a count - note that doing .count on comments still uses a count
statement).

Hope that''s useful...

Andrew

-----Original Message-----
From: rails-bounces@lists.rubyonrails.org
[mailto:rails-bounces@lists.rubyonrails.org] On Behalf Of Chris Schumann
Sent: 03 April 2006 16:31
To: rails@lists.rubyonrails.org
Subject: Re: [Rails] Order By Number of Comments
> Date: Mon, 3 Apr 2006 16:36:15 +0200
> From: Hamza <hamzakc@gmail.com>
> def show_discussed
>   @contents.find(:all, :order => "contents.comment.size DESC",
:joins
> =>
> "comments")
> end
As Francois pointed me to, you want sort_by. find returns an array, and
array mixes in Enumerable.

http://www.ruby-doc.org/core/classes/Enumerable.html#M002092

So something like this:

@contents.find(:all)
@contents.sort_by(|x| f(x))

Where f(x) is code that evaluates the number you want to sort on, like
the number of comments... Comment.count(:conditions => "content_id =
?",
x.id)

Chris S


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