Ruby 多对多关系：通过给予'；找不到关联'；错误

在我的模型中，

项目

由

用户

创建，可以由许多

用户

购买，而

用户

可以购买许多

项目

用户

、

项目

和

购买

使用

AcvtiveRecord

进行定义，为简洁起见，删除了多余的细节，如下所示：

class User < ActiveRecord::Base
  # various other fields
  has_many :items, :foreign_key => :creator_id
  has_many :purchased_items, :through => :purchases, :source => :item
end

class Item < ActiveRecord::Base
  # various other fields
  belongs_to :creator, :class_name => 'User'
  has_many :buyers, :through => :purchases, :source => :user
 end

 class Purchase < ActiveRecord::Base
   belongs_to :item
   belongs_to :user
  # various other fields
 end

describe "user purchasing" do
  it "should allow a user to purchase an item" do
    a_purchase = Purchase.create!(:item => @item, # set up in `before :each`
                                  :user => @user  # set up in `before :each`
    )
    a_purchase.should_not eq(nil)                 # passes
    @item.buyers.should include @user             # fails
    @user.purchased_items.should include @item    # fails
  end
end

这导致

1) Purchase user purchasing should allow a user to purchase an item
   Failure/Error: @item.buyers.should include @user
   ActiveRecord::HasManyThroughAssociationNotFoundError:
     Could not find the association :purchases in model Item

同样，如果我交换

@file_item.bullers.应该包括@user

和

@user.purchased_items.应该包括@item

，我会得到等价物

1) Purchase user purchasing should allow a user to purchase an item
   Failure/Error: @user.purchased_items.should include @item
   ActiveRecord::HasManyThroughAssociationNotFoundError:
     Could not find the association :purchases in model User

我的

迁移

看起来像

create_table :users do |t|
  # various fields
end

create_table :items do |t|
  t.integer :creator_id   # file belongs_to creator, user has_many items
  # various fields
end

create_table :purchases do |t|
  t.integer :user_id
  t.integer :item_id
  # various fields
end

---

我做错了什么？

您必须指定以下内容

class User < ActiveRecord::Base
  has_many :purchases
  has_many :items, :foreign_key => :creator_id
  has_many :purchased_items, :through => :purchases, :source => :item
end

class Item < ActiveRecord::Base
  # various other fields
  has_many :purchases
  belongs_to :creator, :class_name => 'User'
  has_many :buyers, :through => :purchases, :source => :user
end

---

该模型将能够识别关联。

如果在用户和项目中删除

，：source=>：item

，则会发生什么？好问题。我只是试了一下，没什么不同。我仍然得到

找不到关联：在模型项中购买

（反之亦然）。

      has_many :purchases