include vs joins

http://railscasts.com/episodes/181-include-vs-joins
<br />User.all(:joins => :comments, :select => "users.*, count(comments.id) as comments_count", :group => "users.id")<br /><br /><br />g = Group.first<br />Comment.all(:joins => {:user => :memberships}, :conditions => { :memberships => { :group_id => g.id } })<br /><br /># models/comment.rb<br />class Comment < ActiveRecord::Base<br /> belongs_to :user<br />end<br /><br /># models/user.rb<br />class User < ActiveRecord::Base<br /> has_many :memberships<br /> has_many :groups, :through => :memberships<br /> has_many :comments<br />end<br /><br /># models/membership.rb<br />class Membership < ActiveRecord::Base<br /> belongs_to :user<br /> belongs_to :group<br />end<br /><br /><br /># models/group.rb<br />class Group < ActiveRecord::Base<br /> has_many :memberships<br /> has_many :users, :through => :memberships<br /> #rails does not support nested association<br /><br /> def comments<br /> Comment.scoped(:joins => {:user => :memberships}, :conditions => { :memberships => { :group_id => id } })<br /> end<br />end<br /><br />