rails 中的 4 个模型是否可能存在 has_many 关系? [英] Is a has_many through relationship possible with 4 models in rails?

问题描述

例如，一个列表和一个子列表可以通过名为 list_items 的模型拥有多个项目.

For example a list and a sublist can have many items through a model called list_items.

这是模型

class List < ActiveRecord::Base
    has_many :sublists
    has_many :list_items
    has_many :items, through: :list_items
end

class Sublist < ActiveRecord::Base
    belongs_to :list
    has_many :list_items
    has_many :items, through: :list_items
end

class Item < ActiveRecord::Base
    has_many :list_items
    has_many :lists,through: :list_items
    has_many :sublists, through: :list_items
end

class ListItem < ActiveRecord::Base
  belongs_to :list
  belongs_to :sublist
  belongs_to :item
end

这就是我想要完成的.

项目库页面

Item 1
Item 2
Item 3
Item 4
Item 5 

列表页面

=============================
=List 1                     =
=============================
=Item 2                     =
=Item 4                     =
=Sublist Start              =
=Item 5                     =
=Item 1                     =
=Item 3                     =
=============================

因此，没有子列表的项目(如项目 2 和项目 4)将在 List_Item 模型中填充以下字段

So an item without a sublist (like item 2 and item 4) would have the following fields populated in the List_Item Model

List_id = 1

Sublist_id = nil

Item_id = 1

具有子列表的项目(如项目 5、项目 1 和项目 3)将在 List_Item 模型中填充以下字段

An item with a sublist (like item 5 and item 1 and item 3) would have the following fields populated in the List_Item Model

List_id = 1

Sublist_id = 1

Item_id = 1

我想这样做的原因是我可以通过拖动到子列表来进行拖放操作，它将填充 sublist_id，然后从子列表中拖出 sublist_id 将为零.

The reason i would like to do it this way is so i can do drag and drop by dragging to the sublist it will populate the sublist_id and by dragging out of the sublist the sublist_id will then be nil.

这是可能的还是有更好的方法来做到这一点?

Would this be possible or is there a better way to do this this?

推荐答案

回答您的问题:是的，这是可能的:

To answer your question: Yes, that's possible:

class A
  has_many :bs
  has_many :cs, through: :bs
  has_many :ds, through: :cs
end

class B
  has_many :cs
  belongs_to :a
end

class C
  has_many :ds
  belongs_to :b
end

class D
  belongs_to :c
end

如果 A 上的关联与 B 上的关联命名不同，则需要将 source 参数提供给 through 关系，如下所示:

If th association on A is named differently than the association on B, you need to supply the source parameter to the through-relation, like this:

class A
  has_many :bs
  has_many :cs, through: :bs, source: :ccs
end

class B
  has_many :cs, as: :ccs
  belongs_to :a
end

class C
  belongs_to :b
end

这将允许您:

A.find(1).bs # => collection of B-instances
A.find(1).cs # => collection of C-instances

我不确定，这是否能回答您的问题.我希望如此，但我对你的例子有点困惑，所以如果没有，请发表评论:)

I'm not sure, if this answers your question. I hope so, but I'm a little confused about your example, so if not, please do comment :)

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