Question

我试图在关于铁路项目的鲁比项目中做以下工作:

class FoodItem < ActiveRecord::Base
  has_and_belongs_to_many :food_categories
  has_many :places, :through => :food_categories
end

class FoodCategory < ActiveRecord::Base
  has_and_belongs_to_many :food_items
  belongs_to :place
end

class Place < ActiveRecord::Base  
  has_many :food_categories
  has_many :food_items, :through => :food_category
end

但称之为“试样方法”some_food_item.places。我有以下错误:

ActiveRecord::StatementInvalid: PGError: ERROR:  column 
food_categories.food_item_id does not exist
LINE 1: ...laces".id = "food_categories".place_id    WHERE (("food_cate...

: SELECT "places".* FROM "places"  INNER JOIN "food_categories" ON "places".id = "food_categories".place_id    WHERE (("food_categories".food_item_id = 1))

什么是完美的,因为关于粮食电离层和食品箱的HABTMs I有名为的食品分类——食品——项目的制图表。

我必须做些什么才能通过制图表正确检查位置,而不是在<食品-类别表中寻找<食品>项目_id?

Answer 1

我的第一版答案是不正确的,但这是完美的。我第一次做了两件打字(实际上不会制造检测器的危险),但这次我进行了核实。还需要一种假想,但这是容易的。第一,安装花板:

script/plugin install git://github.com/ianwhite/nested_has_many_through.git

安装了伊恩·怀特工场,不间断地工作。如今,这些模型从测试表一中直接复制,以完成这项工作:

class FoodItem < ActiveRecord::Base
  has_many :food_category_items
  has_many :food_categories, :through => :food_category_items
  has_many :places, :through => :food_categories
end

class FoodCategory < ActiveRecord::Base
  has_many :food_category_items
  has_many :food_items, :through => :food_category_items
  belongs_to :place
end

class FoodCategoryItem < ActiveRecord::Base
  belongs_to :food_item
  belongs_to :food_category
end

class Place < ActiveRecord::Base
  has_many :food_categories
  has_many :food_category_items, :through => :food_categories
  has_many :food_items, :through => :food_category_items
end

如今,“农场”协会也同样发挥作用。 <代码>_instance.food_items and food_item.places both work flawlessly, as well as the briefr Associations involved. 仅供参考,我在此图示着所有外国钥匙的去向:

create_table "food_categories", :force => true do |t|
  t.string   "name"
  t.integer  "place_id"
  t.datetime "created_at"
  t.datetime "updated_at"
end

create_table "food_category_items", :force => true do |t|
  t.string   "name"
  t.integer  "food_item_id"
  t.integer  "food_category_id"
  t.datetime "created_at"
  t.datetime "updated_at"
end

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

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

希望这一帮助!

<><>UPDATE: 这个问题最近几次出现。我写了一篇文章,,其中阐明你的才能:通过的关系,详细解释。甚至在Gite Hub有下载和玩.的附带例子。

Answer 2

几个月前,我写了 ,这是关于的一篇文章。简言之,has_many 铁路公司不允许通过<条码>、_和_造船_to_many的协会。然而,你可以部分地模仿关系,这样做的就是:

class FoodItem < ActiveRecord::Base
  has_and_belongs_to_many :food_categories
  named_scope :in_place, lambda{ |place|
    {
      :joins      => :food_categories,
      :conditions => {:food_categories => {:id => place.food_category_ids}},
      :select     => "DISTINCT `food_items`.*" # kill duplicates
    }
  }
end

class FoodCategory < ActiveRecord::Base
  has_and_belongs_to_many :food_items
  belongs_to :place
end

class Place
  has_many :food_categories
  def food_items
    FoodItem.in_place(self)
  end
end

将向您提供<条码>部分——食品——项目<>。您寻求的方法。

Answer 3

使用铁路3.2.13和Rasmus的Im, 您的原始装置现在似乎在HABTM上工作。

我建议用户首先尝试工作。

Answer 4

这样做是正确的,因为你可以在一席上“走许多路”。从本质上讲,你试图将关系扩大的程度比你真的要好。 HABTM (has_and_belongs_to_many)不是解决大多数问题的非常有力的办法。

就你而言,我建议添加一个称为“粮食作物”的模式,并重新命名您的加入表格。你们还需要补充主要领域。之后,建立了你这样的示范协会:

class FoodItem < ActiveRecord::Base
  has_many :food_categories, :through => :food_category_items
  has_many :places, :through => :food_categories
end

class FoodCategory < ActiveRecord::Base
  has_many :food_items, :through => :food_category_items
  belongs_to :place
end

class FoodCategoryItems < ActiveRecord::Base
  belongs_to :food_item
  belongs_to :food_category
end

class Place < ActiveRecord::Base  
  has_many :food_categories
  has_many :food_items, :through => :food_categories
end

注:我还在“Place->”中确定了一个字体;它有:食品-项目。这应当照顾到你们的需要,并给你额外红利,使其能够在今后为你的粮食作物“就业”模式增加功能。

友情链接