如何在Rails / ActiveRecord中加载多态has_many :through
关联?
以下是基本设置:
class Post < ActiveRecord::Base
has_many :categorizations, :as => :categorizable
has_many :categories, :through => :categorizations
end
class Category < ActiveRecord::Base
has_many :categorizations, :as => :category
has_many :categorizables, :through => :categorizations
end
class Categorization < ActiveRecord::Base
belongs_to :category, :polymorphic => true
belongs_to :categorizable, :polymorphic => true
end
假设我们想要解决Rails 2.3.x的这个急切加载问题以及连接模型上的双重多态关联,那么如何在这样的事情上加载:through
关联:
posts = Post.all(:include => {:categories => :categorizations})
post.categories # no SQL call because they were eager loaded
那不行,有什么想法吗?
答案 0 :(得分:0)
使用has_many:through更容易实现。您是否有特定原因想要使用多态关联?
使用has_many:通过您可以使用此ActiveRecord查询
posts = Post.all(:include => [:categorizations, :categories])
posts[0].categories # no additional sql query
posts[0].categorizations # no additional sql query
模型定义
class Post < ActiveRecord::Base
has_many :categorizations
has_many :categories, :through => :categorizations
end
class Category < ActiveRecord::Base
has_many :categorizations
has_many :posts, :through => :categorizations
end
class Categorization < ActiveRecord::Base
belongs_to :post
belongs_to :category
end
使用这些迁移
class CreatePosts < ActiveRecord::Migration
def self.up
create_table :posts do |t|
t.string :title
t.timestamps
end
end
def self.down
drop_table :posts
end
end
class CreateCategories < ActiveRecord::Migration
def self.up
create_table :categories do |t|
t.string :name
t.timestamps
end
end
def self.down
drop_table :categories
end
end
class CreateCategorizations < ActiveRecord::Migration
def self.up
create_table :categorizations do |t|
t.integer :post_id
t.integer :category_id
t.timestamps
end
end
def self.down
drop_table :categorizations
end
end