获得满足两个has_many的条件的记录:通过。

Let's say I have 3 models in my Rails app... Establishment, WasteType and EstablishmentWaste... My problem is that I want to get all establishments associated with a certain wastetype. This normally would be done with Establishment.where(waste_type_id: some_number), the problem is that Establishment has many WasteType and vice versa, and the association is made through a third party...

假设我有3个模型在我的Rails应用中…建立,WasteType EstablishmentWaste……我的问题是我想要所有与某种废物类型相关的设施。这通常是建立起来的。在(waste_type_id: some_number)中，问题是建立有很多的废物类型，反之亦然，关联是通过第三方建立的……

Any help?

任何帮助吗?

Classes and data model below

类和数据模型如下

Establishment

建立

class Establishment < ActiveRecord::Base
  # Include default devise modules.
  devise :database_authenticatable, :registerable,
          :recoverable, :rememberable, :trackable, :validatable, :omniauthable

    has_many :containers
    has_many :establishment_wastes
    has_many :waste_types, through: :establishment_wastes, :foreign_key => 'establishment_id'

  include DeviseTokenAuth::Concerns::User
end

WasteType

WasteType

class WasteType < ActiveRecord::Base

    has_many :containers
    has_many :establishment_wastes
    has_many :establishments, through: :establishment_wastes, :foreign_key => 'waste_type_id'

end

EstablishmentWaste

EstablishmentWaste

class EstablishmentWaste < ActiveRecord::Base

    belongs_to :establishment, :foreign_key => 'establishment_id' 
    belongs_to :waste_type, :foreign_key => 'waste_type_id'

end

So the data model would be like these

数据模型是这样的

1 个解决方案

#1

EstablishmentWaste is a join table in this case so the query should be.

在这种情况下，builshmentwaste是一个连接表，因此查询应该是。

Establishment
 .joins(:establishment_wastes)
 .where('establishment_wastes.waste_type_id = ?', some_number)

Quick tip! You do not need to assign :foreign_key => 'establishment_id' since it is default Rails behavior to assign a foreign key to model_id.

快提示!您不需要分配:foreign_key => ' builshment_id '，因为它是为model_id指定一个外键的默认Rails行为。

#1