count_from_query gives you the ability to generate a COUNT query from
a standard Rails find.
For example, if you have the query
User.find :all
it would be trivial to get a count:
User.count
however, if you have a more specific finder method, such as
class Company < ActiveRecord::Base
def complete_videos
Video.find :all, :conditions => “company_id=#{id} AND
status=‘complete’”, :order => “created_at DESC”
end
end
Getting the count isn’t quite as easy. You could just call #size on
the returned array, but it’s wasteful if you don’t actually need the
records. You could write a complete_videos_count method, but it
doesn’t feel very DRY to have two methods every time you want to do a
count query as well.
With count_from_query, it’s cake
videos_count = ActiveRecord::Base.count_from_query {
my_company.complete_videos }
You can wrap any AR find call in count_from_query to have it be
converted into a count query.
Association proxies work the same way. We could change the
complete_videos definition to be
class Company < ActiveRecord::Base
def complete_videos
videos.find :all, :conditions => “status=‘complete’”, :order =>
“created_at DESC”
end
end
and get the same result.
ruby script/plugin install
svn://evang.eli.st/public/plugins/count_from_query
Released under the MIT License