My models look like this:
class Movie < ActiveRecord::Base
attr_accessible :title, :year, :rotten_id, :audience_score,
:critics_score, :runtime, :synopsis, :link, :image
has_many :jobs, :dependent => :destroy
has_many :actors, :through => :jobs
end
class Actor < ActiveRecord::Base
attr_accessible :name
has_many :movies, :through => :jobs
has_many :jobs, :dependent => :destroy
end
class Job < ActiveRecord::Base
attr_accessible :movie_id, :actor_id
belongs_to :movie
belongs_to :actor
end
When I'm displaying my index of Actors, I'd like to show the number of movies each actor has starred in. I can do this with @actor.movies.count
, however this generates an SQL query for each actor
. With, say, 30 actors, this will result in 30 extra queries in addition to the initial.
Is开发者_JAVA百科 there any way to include the count of movies each actor has participated in, in the initial Actor.all
call? And thereby getting things done with only one call. Extra bonus if this was sorted by said count.
Update:
All answers provided has been helpful, and though it turned into some dirt-slinging-contest at some point, it worked out well. I did a mish-mash of all your suggestions. I added a movies_counter column to my Actor model. In my Job model I added belongs_to :actor, :counter_cache => :movies_counter
. This works brilliantly, and is automatically updated when i create or destroy a movie, without me adding any further code.
As @Sam noticed, you should add new column to actors
table movies_counter
rails g migration add_movies_counter_to_actor movies_counter:integer
Now you can edit your migration
class AddMoviesCounterToActor < ActiveRecord::Migration
def self.up
add_column :actors, :movies_counter, :integer, :default => 0
Actor.reset_column_information
Actor.all.each do |a|
a.update_attribute :movies_counter, a.movies.count
end
end
def self.down
remove_column :actors, :movies_counter
end
end
And run it
rake db:migrate
Then you should add two callbacks: after_save
and after_destroy
class Movie < ActiveRecord::Base
attr_accessible :title, :year, :rotten_id, :audience_score,
:critics_score, :runtime, :synopsis, :link, :image
has_many :jobs, :dependent => :destroy
has_many :actors, :through => :jobs
after_save :update_movie_counter
after_destroy :update_movie_counter
private
def update_movie_counter
self.actors.each do |actor|
actor.update_attribute(:movie_count, actor.movies.count)
end
end
end
Then you can call some_actor.movies_counter
Add a column to your Actor table called 'movie_count'. Then add a call back in your Actor model that updates that column.
class Movie < ActiveRecord::Base
has_many :actors, :through => :jobs
before_save :update_movie_count
def update_movie_count
self.actor.update_attribute(:movie_count, self.movies.size)
end
end
That way your just have an integer that gets updated instead of calling all records.
精彩评论