模型关系问题

发布于 2024-08-12 19:25:01 字数 767 浏览 2 评论 0原文

我正在尝试根据以下模型关联计算类别中所有条目的平均（平均）评级...

class Entry < ActiveRecord::Base      
  acts_as_rateable
  belongs_to :category
  ...
end


class Category < ActiveRecord::Base
  has_many :entry
  ...
end


class Rating < ActiveRecord::Base
  belongs_to :rateable, :polymorphic => true
  ...
end

评级模型由充当可评级插件，因此可评级模型如下所示...

  module Rateable #:nodoc:
  ...

    module ClassMethods
      def acts_as_rateable
        has_many :ratings, :as => :rateable, :dependent => :destroy
        ...
      end
    end
    ...
  end

我如何执行平均计算？这可以通过 Rails 模型关联来完成还是必须求助于 SQL 查询？

原文

I am trying to calculate the average (mean) rating for all entries within a category based on the following model associations ...

class Entry < ActiveRecord::Base      
  acts_as_rateable
  belongs_to :category
  ...
end


class Category < ActiveRecord::Base
  has_many :entry
  ...
end


class Rating < ActiveRecord::Base
  belongs_to :rateable, :polymorphic => true
  ...
end

The rating model is handled by the acts as rateable plugin, so the rateable model looks like this ...

  module Rateable #:nodoc:
  ...

    module ClassMethods
      def acts_as_rateable
        has_many :ratings, :as => :rateable, :dependent => :destroy
        ...
      end
    end
    ...
  end

How can I perform the average calculation? Can this be accomplished through the rails model associations or do I have to resort to a SQL query?

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你与清晨阳光 2024-08-19 19:25:01

平均方法可能就是您正在寻找的方法。以下是根据您的情况使用它的方法：

@category.entries.average('ratings.rating', :joins => :ratings)

The average method is probably what you're looking for. Here's how to use it in your situation:

@category.entries.average('ratings.rating', :joins => :ratings)

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梦魇绽荼蘼 2024-08-19 19:25:01

您可以在模型上使用named_scope 或自定义方法吗？不管怎样，它仍然需要一些 SQL，因为如果我理解这个问题，你正在计算一个值。

在传统的数据库应用程序中，这将是数据表的视图。

因此，在这种情况下，您可能会做类似的事情...（注意未经过测试或确定它是 100% 完成的）

class Category  
  has_many :entry do  
    def avg_rating()  
       @entries = find :all
       @entres.each do |en|
          @value += en.rating
    end  
    return @value / entries.count
  end


 end

Could you use a named_scope or custom method on the model. Either way it would still require some SQL since, if I understand the question, your are calculating a value.

In a traditional database application this would be a view on the data tables.

So in this context you might do something like... (note not tested or sure it is 100% complete)

class Category  
  has_many :entry do  
    def avg_rating()  
       @entries = find :all
       @entres.each do |en|
          @value += en.rating
    end  
    return @value / entries.count
  end


 end

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过度放纵 2024-08-19 19:25:01

编辑 - 查看 EmFi 的修订答案。

我不做任何承诺，但试试这个

class Category
  def average_rating    
    Rating.average :rating, 
      :conditions => [ "type = ? AND entries.category_id = ?", "Entry", id ],
      :join => "JOIN entries ON rateable_id = entries.id"
  end
end

Edit - Check out EmFi's revised answer.

I make no promises but try this

class Category
  def average_rating    
    Rating.average :rating, 
      :conditions => [ "type = ? AND entries.category_id = ?", "Entry", id ],
      :join => "JOIN entries ON rateable_id = entries.id"
  end
end

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