它看起来像你基本上建模一个has_many :through
关系:项目has_and_belongs_to_many用户和评级是联接模型。您可以在Rails Guide to Active Record Associations中阅读关于:through
关系。
如果是这样的话,我会建议使用has_many :through
如下构建模型的关系:
class Rating < ActiveRecord::Base
attr_accessible :item_id, :user_id
belongs_to :item
belongs_to :user
end
class User < ActiveRecord::Base
has_many :ratings
has_many :rated_items, :through => :ratings
end
class Item < ActiveRecord::Base
has_many :ratings
has_many :rated_by_users, :through => :ratings, :source => :user
end
然后,说你有在DB以下记录:
$ sqlite3 db/development.sqlite3 'SELECT * FROM items';
1|2013-03-22 03:21:31.264545|2013-03-22 03:21:31.264545
2|2013-03-22 03:24:01.703418|2013-03-22 03:24:01.703418
$ sqlite3 db/development.sqlite3 'SELECT * FROM users';
1|2013-03-22 03:21:28.029502|2013-03-22 03:21:28.029502
$ sqlite3 db/development.sqlite3 'SELECT * FROM ratings';
1|1|1|2013-03-22 03:22:01.730235|2013-03-22 03:22:01.730235
你可以要求的项目,与他们相关的评分和用户实例,一起这样的说法:
items = Item.includes(:rated_by_users)
此执行3个您的SQL查询:
Item Load (0.1ms) SELECT "items".* FROM "items"
Rating Load (0.2ms) SELECT "ratings".* FROM "ratings" WHERE "ratings"."item_id" IN (1, 2)
User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."id" IN (1)
,并试图访问用户(一个或多个),其额定每个项目可以通过调用每个项目的#rated_by_users
联想法来完成:
> items.map {|item| item.rated_by_users }
=> [[#<User id: 1, created_at: "2013-03-22 03:21:28", updated_at: "2013-03-22 03:21:28">], []]
检查此链接。 http://stackoverflow.com/questions/4197418/rails-3-eager-loading-with-conditions – 2013-03-21 08:57:42
请包括用户模型 – gabrielhilal 2013-03-21 09:08:23
@AbibullahRahamathulah这个问题是关于静态参数(has_many条件),而不是动态的 – thejaz 2013-03-21 09:16:15