HABTM關係和加入表

Question

我試圖連接的兩個連接，我已經和展示基於條件的關係，結果表中的值......，我有一些問題

我有一個用戶模型（：名稱，密碼，電子郵件）和事件模型（：名稱，等）和興趣模型（：名稱）

我在每個模型中創建了約5條記錄。

然後我創建了兩個連接表 - > UsersInterests和EventsInterests;每個不包含主鍵並且分別僅由user_id/interest_id和event_id/interest_id組成。

然後我加入到模型文件的HABTM關係

users => has_and_belongs_to_many :interests 
events => has_and_belongs_to_many :interests 
interests => has_and_belongs_to_many :users 
     has_and_belongs_to_many :events 

現在我想創建一個控制器，發現只有在用戶利益的事件對應的事件感興趣

從這工作一會兒，我計算過，我需要的東西在

@Events = Event.User.find([condition]) 
[condition] = where users.interest == event.interest 

或類似的東西的地區...我是那種lost..How做你的狀態的網絡連接nd條件？...我知道如何做的內部連接在SQL中，但我正在尋找優雅的Rails的方式來做到這一點...任何提示球員？

Answer 1

優雅的紅寶石方式是named scopes。但是，因爲您決定使用has_and_belongs_to_many關係而不是has_many：通過關係，您將需要使用原始SQL定義聯接，這不是很優雅。由於Rails處理SQL生成的方式，您將必須爲單個用戶創建一個範圍，併爲第二個命名範圍提供許多用戶的使用範圍。

Class Event < ActiveRecord::Base 
    ... 

    #find events that share an interest with a single user 
    named_scope :shares_interest_with_user, lambda {|user| 
    { :joins => "LEFT JOIN events_interests ei ON ei.event_id = events.id " + 
     "LEFT JOIN users_intersets ui ON ui.interest_id = ei.interest_id", 
     :conditions => ["ui.user_id = ?", user], :group_by => "events.id" 
    } 

    #find events that share an interest with a list of users 
    named_scope :shares_interest_with_users, lambda {|users| 
    { :joins => "LEFT JOIN events_interests ei ON ei.event_id = events.id " + 
     "LEFT JOIN users_intersets ui ON ui.interest_id = ei.interest_id", 
     :conditions => ["ui.user_id IN ?", users], :group_by => "events.id" 
    }  
    } 

    #find events that share an interest with any user 
    named_scope :shares_interest_with_any_user, lambda { 
    { :joins => "LEFT JOIN events_interests ei ON ei.event_id = events.id " + 
     "JOIN users_intersets ui ON ui.interest_id = ei.interest_id", 
     :conditions => "ui.user_id IS NOT NULL", :group_by => "events.id" 
    }  
    } 

end 

現在你可以這樣做是爲了讓所有的事件，一個用戶可能感興趣的：

@events = Event.shares_interest_with_user(@user) 

或者，這讓所有的活動用戶的列表可能感興趣的：

@events = Event.shares_interest_with_users(@users) 

但正如我所警告的那樣，那不是真的優雅。

如果您通過與適當的連接模型而非HABTM關係的關係重新定義關係爲has_many，則可以大大簡化連接。你的情況將需要nested has many through plugin這個工作。注：您必須在所有其他模型中添加相應的has_many/belongs_to語句。即使是加入模型。

Class Event < ActiveRecord::Base 
    has_many :event_interests 
    has_many :interests, :through => :event_interests 
    has_many :user_interests, :through => :interests 
    has_many :users, :through => :user_interests 
    ... 

    #find events that share an interest with a list of users 
    named_scope :shares_interest_with_users, lambda {|user| 
    { :joins => :user_interests, :group_by => "events.id", 
     :conditions => {:user_interests => {:user_id => user}} 
    }  
    } 

    #find events that share an interest with any user 
    named_scope :shares_interest_with_any_user, lambda { 
    { :joins => :user_interests, :group_by => "events.id", 
     :conditions => "user_interests.user_id IS NOT NULL" 
    } 

end 

現在，下面的工作。

@user = User.first; @users = User.find(1,2,3) 

# @events = all events a single user would be interested in 
@events = Event.shares_interest_with_users(@user) 

# @events = all events any of the listed users would be interested in. 
@events = Event.shares_interest_with_users(@user) 

你甚至可以定義一個名爲範圍，選擇尚未發生的事件和連鎖兩種：

named_scope :future_events, lambda { 
    { :conditions => ["start_time > ?", Time.now]} 
} 

Events.future_events #=> Events that haven't started yet. 

# Events that a user would be interested in but only choose those 
# that haven't started yet. 
Events.future_events.shares_interest_with_user(@user)