优雅的 ruby 方法是使用命名范围。但是,因为您决定使用 has_and_belongs_to_many 关系而不是 has_many :through 关系,所以您将需要使用原始 SQL 定义连接,这不是很优雅。而且由于 Rails 处理 SQL 生成的方式,您必须创建一个供单个用户使用的范围,以及另一个用于多个用户的命名范围。
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
现在您可以这样做来获取用户可能感兴趣的所有事件:
@events = Event.shares_interest_with_user(@user)
或者这是获取用户列表可能感兴趣的所有事件:
@events = Event.shares_interest_with_users(@users)
但正如我警告的那样,这并不是很优雅。
如果通过正确的连接模型而不是 HABTM 关系将关系重新定义为 has_many,则可以大大简化连接。你的情况需要嵌套的有很多通过插件才能工作。注意您必须在所有其他模型中添加相应的 has_many/belongs_to 语句。甚至连接模型。
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
现在,以下将起作用。
@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)
您甚至可以定义一个命名范围来选择尚未发生的事件并将两者链接起来:
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)