Rails 4：结合 has_many ：通过关联与多态关联

Question

在我的 Rails 4 应用程序中，我有以下模型：

User
has_many :administrations
has_many :calendars, through: :administrations
has_many :comments
has_many :calendar_comments, through: :calendars, :source => :comments

Calendar
has_many :administrations
has_many :users, through: :administrations
has_many :posts
has_many :comments, through: posts
has_many :ads

Administration
belongs_to :user
belongs_to :calendar

Post
belongs_to :calendar
has_many :comments, as: :commentable

Ad
belongs_to :calendar
has_many :comments, as: :commentable

Comment
belongs_to :commentable, polymorphic: true
belongs_to :user

我需要从calendar 和ad belongs_to 访问comments、belong_to 和ad。

这就是我在Calendars#Index 操作中尝试做的事情：

@posts_comments = @user.calendar_comments.where(commentable_type: "Post").order("created_at DESC").limit(5)
@ads_comments = @user.calendar_comments.where(commentable_type: "Ad").order("created_at DESC").limit(5)

我的第一个猜测是在日历模型中添加has_many :comments, through: ads：

Calendar
has_many :administrations
has_many :users, through: :administrations
has_many :posts
has_many :comments, through: posts
has_many : ads
has_many :comments, through: ads

但这取消了has_many :comments, through: posts的效果，然后我不能再从calendarpostbelongs_to访问commentsbelong_to和post。

有没有办法让 BOTH has_many :comments, through: posts AND has_many :comments, through: ads 工作？

————

更新：根据this article和that Stack Overflow question，答案可能在于source:和source_type:的使用。

但不知道如何使用这些。

————

更新 2：下面的代码有意义吗？

class Calendar < ActiveRecord::Base
  has_many :administrations, dependent: :destroy
  has_many :users, through: :administrations
  has_many :posts, dependent: :destroy
  has_many :commented_posts, through: :comments, source: :commentable, source_type: 'Post'
  has_many :ads, dependent: :destroy
  has_many :commented_ads, through: :comments, source: :commentable, source_type: 'Ad'

————

更新 3：当我尝试上面的代码时，我收到以下错误消息：

Could not find the source association(s) :comments in model Calendar. Try 'has_many :calendar_comments, :through => :calendars, :source => <name>'. Is it one of administrations, users, posts, commented_posts, ads, commented_ads, invites, or pokes?

我尝试了以下方法：

class Calendar < ActiveRecord::Base
  has_many :administrations, dependent: :destroy
  has_many :users, through: :administrations
  has_many :posts, dependent: :destroy
  has_many :calendar_comments, :through => :calendars, :source => :post
  has_many :ads, dependent: :destroy
  has_many :calendar_comments, :through => :calendars, :source => :ad

————

更新 4：使用以下代码的新尝试失败：

class Calendar < ActiveRecord::Base
  has_many :administrations, dependent: :destroy
  has_many :users, through: :administrations
  has_many :posts, dependent: :destroy
  has_many :calendar_comments, :through => :commentable, :source => :post
  has_many :ads, dependent: :destroy
  has_many :calendar_comments, :through => :commentable, :source => :ad

还是不行，和上面一样的错误信息。

————

更新 5：根据 MrYoshiji 的回答，我现在有了

class Calendar < ActiveRecord::Base
  has_many :administrations, dependent: :destroy
  has_many :users, through: :administrations
  has_many :posts, dependent: :destroy
  has_many :posts_comments, through: :posts, source_type: 'Post'
  has_many :ads, dependent: :destroy
  has_many :ads_comments, through: :ads, source_type: 'Ad'

现在，User 模型中的 has_many :calendar_comments, through: :calendars, :source => :comments 不再工作。

我试过了：

has_many :comments
has_many :calendar_post_comments, through: :calendars, :source => :post_comments
has_many :calendar_ad_comments, through: :calendars, :source => :ad_comments

还是不行。

————

更新 6：我仍然被这个问题困扰，因为我无法找到让以下代码正常工作的方法：

@posts_comments = @user.calendar_comments.where(commentable_type: "Post").order("created_at DESC").limit(5)
@ads_comments = @user.calendar_comments.where(commentable_type: "Ad").order("created_at DESC").limit(5)

我尝试了很多不同的方法，到目前为止我能想到的最好的方法是：

class Calendar < ActiveRecord::Base
  has_many :administrations, dependent: :destroy
  has_many :users, through: :administrations
  has_many :posts, dependent: :destroy
  has_many :post_comments, through: :posts, source_type: 'Post'
  has_many :ads, dependent: :destroy
  has_many :ad_comments, through: :ads, source_type: 'Ad'
end

class User < ActiveRecord::Base
  has_many :administrations, dependent: :destroy
  has_many :calendars, through: :administrations
  has_many :comments
  has_many :calendar_post_comments, through: :calendars, :source => :post_comments
  has_many :calendar_ad_comments, through: :calendars, :source => :ad_comments
end

然后，我更新我的日历控制器如下：

def index
    @user = current_user
    @calendars = @user.calendars.all
    @posts_comments = @user.calendar_post_comments
                              .order("created_at DESC")
                              .limit(5)
    @ads_comments = @user.calendar_ad.comments
                              .order("created_at DESC")
                              .limit(5)
end

但这会返回以下错误：

NoMethodError at /calendars
undefined method `chain' for nil:NilClass
@posts_comments = @user.calendar_post_comments.order("created_at DESC").limit(5)

这里有什么问题？

Answer 1

您应该尝试以下方法：

class Calendar < ActiveRecord::Base
  # [ ... ]
  has_many :posts
  has_many :posts_comments, through: posts, source_type: 'Post'
  has_many :ads
  has_many :ads_comments, through: ads, source_type: 'Ad'

考虑到Ad 和Post 模型都具有以下特性：

has_many :comments, as: :commentable