这个SQL查询的Ruby on Rails代码是什么？

Question

我在Ruby on Rails的noob。我在这里有一个查询，将显示可用的房间/ ammenity。它确实在C＃编程中工作，但我不知道如何在Ruby on Rails中实现它。

Select distinct A.id, A.a_name From Amenities A 
    Where A.id not in 
    (
    Select Aa.id From Amenities Aa, Amenity_List AL Where 
    A.id = AL.amenities_id AND 
     (
      (params[:start_date] BETWEEN AL.checkin AND AL.checkout) OR 
      (params[:end_date] BETWEEN Al.checkin AND AL.checkout) 
     ) 
    ) 
Order by A.id 

帮助。谢谢！ :)

这里是我的模型：

class Amenity < ActiveRecord::Base 
    has_many :amenity_lists 
    has_many :line_items 
end 

class AmenityList < ActiveRecord::Base 

    belongs_to :transaction 
    belongs_to :amenity 

    scope :range, where(:checkin => (params[:start_date])..(params[:end_date]) || :checkout => (params[:start_date])..(params[:end_date])) 

    scope :available, find_by_sql(["Select DISTINCT amenities.id, amenities.a_name" + 
       "where amenities.id NOT IN (Select amenities.id from amenities, amenity_lists where amenity.id = amenity_list.amenities_id AND ?)", :range]) 

末

我这样的代码吧。但它不起作用。我正在尝试显示start_date和end_date给出的所有可用设施。

这里的日志：

c:/Sites/fourk/app/models/amenity_list.rb:6: 
syntax error, unexpected tASSOC, expecting ')' ...ams[:end_date]) || :checkout => (params[:start_date])..(para... ...^c:/Sites/fourk/app/models/amenity_list.rb:6: 
syntax error, unexpected ')', expecting keyword_end 

Answer 1

好吧，我想你想找到可用的设施---那些没有预订。

我会建议使用named_scope而不是scope，并将其定义移动到Amenity类，因为你想找到可用的设施。

一个可能的解决方案是使用一个名为范围与嵌入式SQL查询：

class Amenity < ActiveRecord::Base 
    has_many :amenity_lists 

    named_scope :available, lambda { 
    |start_date, end_date| { 
     :select => 'amenities.*', 
     :order => 'id', 
     :conditions => [" 
     amenities.id NOT IN 
     (
      SELECT aa.id from amenities aa, amenity_lists al WHERE 
      amenities.id = al.amenity_id AND 
      (
      (? BETWEEN al.checkin AND al.checkout) OR 
      (? BETWEEN al.checkin AND al.checkout) 
     ) 
     )", 
     start_date, 
     end_date 
     ] 
    } 
    } 
end 

只要注意在Ruby中，字符串可以跨越多行。

现在你可以使用给定的命名范围是这样的：

​​

这将产生以下SQL查询：

SELECT amenities.* FROM "amenities" 
WHERE (
amenities.id NOT IN 
(
    SELECT aa.id from amenities aa, amenity_lists al 
    WHERE 
    amenities.id = al.amenity_id AND 
    (
    ('2011-05-10 23:57:09' BETWEEN al.checkin AND al.checkout) OR 
    ('2011-05-10 23:57:09' BETWEEN al.checkin AND al.checkout) 
    ) 
) 
) ORDER BY id 

另外，如果你是新来的Rails的世界里，我强烈推荐您观看瑞安贝茨的Railscasts系列。第108集约为named_scope。看完之后，请耐心等待，并从第1集开始。:)