#181 Include vs Joins

Sep 28, 2009 | 11 minutes | Active Record

The :include and :joins options for the find method can be a little confusing because they are so similar. In this episode I show specifically when to use which option.

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          script/console
        
ActiveRecord::Base.logger = Logger.new(STDOUT) # to show logs
c = Comment.all(:joins => :user, :conditions => { :users => { :admin => true } })
c.first.users
c = Comment.all(:include => :user, :conditions => { :users => { :admin => true } })
c.first.users
User.all(:joins => :comments, :select => "users.*, count(comments.id) as comments_count", :group => "users.id")
g = Group.first
Comment.all(:joins => {:user => :memberships}, :conditions => { :memberships => { :group_id => g.id } })

          models/comment.rb
        
class Comment < ActiveRecord::Base
  belongs_to :user
end

          models/user.rb
        
class User < ActiveRecord::Base
  has_many :memberships
  has_many :groups, :through => :memberships
  has_many :comments
end

          models/membership.rb
        
class Membership < ActiveRecord::Base
  belongs_to :user
  belongs_to :group
end

          models/group.rb
        
class Group < ActiveRecord::Base
  has_many :memberships
  has_many :users, :through => :memberships
  
  def comments
    Comment.scoped(:joins => {:user => :memberships}, :conditions => { :memberships => { :group_id => id } })
  end
end

          comments_controller.rb
        
def index
  @comments = Comment.all(:joins => :user, :conditions => { :users => { :admin => true } }, :order => "comments.created_at desc")
end

          users_controller.rb
        
def index
  @users = User.all(:joins => :comments, :select => "users.*, count(comments.id) as comments_count", :group => "users.id")
end

          views/groups/show.html.erb
        
<%= render @group.comments %>

          views/users/index.html.erb
        
<%= pluralize user.comments_count, "comment" %>