軌道4：結合的has_many：多態關聯

Question

通過協會在我的Rails 4應用程序，我有以下型號：

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 

我需要從calendar的adbelongs_to訪問comments是belong_to一個ad。

這就是我想在我Calendars#Index動作做到：

@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) 

我的第一個猜測是在日曆模型添加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 

但是取消了對has_many :comments, through: posts效果然後我不能再訪問comments那belong_to和post從calendarpostbelongs_to。

有沒有一種方法，使BOTHhas_many :comments, through: posts和has_many :comments, through: ads工作？

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UPDATE：根據this article和that Stack Overflow question，答案可以在使用source:和source_type:鋪設。

不知道如何使用那些。

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更新2：將下面的代碼作任何意義？

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' 

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更新3：當我嘗試上面的代碼，我得到了以下錯誤消息：

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? 

我試過如下：

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 

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UPDATE 4：一個新的失敗嘗試用以下代碼：

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 

仍然沒有工作，相同的錯誤如上述消息。

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UPDATE 5：基於MrYoshiji的回答，我現在有

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' 

現在，has_many :calendar_comments, through: :calendars, :source => :comments在User模型不再工作。

我想：

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

仍然沒有工作。

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UPDATE 6：我還是堅持了這個問題，因爲我不能想出一個辦法讓下面的代碼工作：

@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) 

我試過很多不同的東西，我能想出迄今爲止最好的是：

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 

然後，我更新我的日曆控制器如下：

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 

但這返回以下錯誤：

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

這裏有什麼問題？

Answer 1

你應該嘗試以下操作：

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' 

考慮到Ad和Post機型都具備以下條件：

has_many :comments, as: :commentable