On Wednesday, May 11, 2011 2:17:01 PM UTC-6, danimashu wrote:
>
> Hello, I have a Post that has_many Comments. I have the next scopes:
>
> scope :valid, where('created_at >= ?', 2.months.ago)
> scope :expired, where('created_at < ?', 2.months.ago)
>
> Now, I would have a scope named :commented that return all the Post
> that have more than 0 Comments but I don't know how do it clearly. A
> solution is have a counter num_comments column in Post, but I don't
> know if that is the best practice.
>
>
It is common for one record type has_many another to "cache" the count of
just how many it has. At least it's common enough that rails can maintain
this counter column for you automagically:
http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#method-i-belongs_to
See the :counter_cache option of the #belongs_to method. With this, you
might have:
class Comment
belongs_to :post, :counter_cache => true
end
class Post
has_many :comments
end
The above example just requires that you have a column in your posts table
named "comments_count". You can use another name, such as your proposed
"num_comments" by instead using:
belongs_to :post, :counter_cache => :num_comments
Anyhow, if you do this then rails will keep this count column up-to-date.
Then you can easily create your desired named scope.
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