Question

以下是我的模特：

class Pizza < ActiveRecord::Base
  belongs_to :pizza_type
  has_many :toppings, through: :pizza_toppings
end

class Topping < ActiveRecord::Base
  belongs_to :topping_type
  has_many :pizza_size_topping_prices
  has_many :pizzas, through: :pizza_toppings
end

class PizzaTopping < ActiveRecord::Base
  belongs_to :pizza
  belongs_to :topping
end

数据库架构

ActiveRecord::Schema.define(version: 20140108194303) do

  create_table "pizza_size_topping_prices", force: true do |t|
    t.integer  "pizza_size_id"
    t.integer  "topping_id"
    t.float    "half_price"
    t.float    "whole_price"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "pizza_sizes", force: true do |t|
    t.string   "name"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "pizza_toppings", force: true do |t|
    t.integer  "pizza_id"
    t.integer  "topping_id"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "pizza_type_size_prices", force: true do |t|
    t.integer  "pizza_size_id"
    t.integer  "pizza_type_id"
    t.float    "base_price"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "pizza_types", force: true do |t|
    t.string   "name"
    t.text     "description"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "pizzas", force: true do |t|
    t.integer  "pizza_type_id"
    t.string   "name"
    t.text     "description"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "topping_types", force: true do |t|
    t.string   "name"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "toppings", force: true do |t|
    t.integer  "topping_type_id"
    t.string   "name"
    t.text     "description"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

end

当我尝试通过white_pizza.toppings找到比萨饼的浇头时，我收到错误：

 ActiveRecord::HasManyThroughAssociationNotFoundError: Could not find the association :pizza_toppings in model Pizza

以下是IRB控制台：

Loading development environment (Rails 4.0.0)
irb(main):001:0> white_pizza = Pizza.last
  Pizza Load (1.1ms)  SELECT "pizzas".* FROM "pizzas" ORDER BY "pizzas"."id" DESC LIMIT 1
=> #<Pizza id: 3, pizza_type_id: 5, name: "first white pizza", description: "first white pizza description", created_at: "2014-01-08 20:20:25", updated_at: "2014-01-08 20:20:25">
irb(main):002:0> white_pizza.toppings
ActiveRecord::HasManyThroughAssociationNotFoundError: Could not find the association :pizza_toppings in model Pizza
    from /home/gcardella/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-4.0.0/lib/active_record/reflection.rb:550:in `check_validity!'
    from /home/gcardella/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-4.0.0/lib/active_record/associations/association.rb:25:in `initialize'
    from /home/gcardella/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-4.0.0/lib/active_record/associations/has_many_through_association.rb:9:in `initialize'
    from /home/gcardella/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-4.0.0/lib/active_record/associations.rb:157:in `new'
    from /home/gcardella/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-4.0.0/lib/active_record/associations.rb:157:in `association'
    from /home/gcardella/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-4.0.0/lib/active_record/associations/builder/association.rb:70:in `toppings'
    from (irb):2
    from /home/gcardella/.rvm/gems/ruby-2.0.0-p0/gems/railties-4.0.0/lib/rails/commands/console.rb:90:in `start'
    from /home/gcardella/.rvm/gems/ruby-2.0.0-p0/gems/railties-4.0.0/lib/rails/commands/console.rb:9:in `start'
    from /home/gcardella/.rvm/gems/ruby-2.0.0-p0/gems/railties-4.0.0/lib/rails/commands.rb:64:in `<top (required)>'
    from bin/rails:4:in `require'
    from bin/rails:4:in `<main>'

任何人都知道为什么会这样吗？我认为基于这种关系，我可以通过这种方式获得披萨的许多配料。请指教。

Answer 1

您的Pizza和Topping类都需要以下行，否则has_many :through部分将无法正常运行：

has_many :pizza_toppings

Rails 4通过关联具有很多功能，不确定关联失败的原因

1 个答案: