Question

我正在使用Kaminari对查询中的一些结果进行分页，其中我选择了不同的记录。请考虑以下控制器代码：

@things = Thing.joins... # create a complex query that produces duplicate results

# I want to select distinct results: this produces the correct results
@things = @things.select("DISTINCT things.*")

# when Kaminari calls count, it will run "SELECT COUNT(*)", instead of 
# "SELECT COUNT(DISTINCT things.*)" we will get the wrong count and extra pages
@things = @things.page(params[:page]).per(10)

我能想到的最佳解决方案是将:distinct => true传递给count，就像this pull request一样，被Kaminari的开发者拒绝了。 This SO question讨论了潜在的问题。 This line of code是对count的违规电话。

是否有任何变通方法可以为Kaminari提供不需要修补Kaminari的正确计数？谢谢。

更新：

使用名为“count”的作用域是一个很好的建议，但在ActiveRecord :: Relation上调用时不起作用。它在我的模型类上调用时有效，但这没有帮助。

Answer 1

请参阅以下网址。

https://github.com/amatsuda/kaminari/pull/77

https://github.com/tbeauvais/kaminari/commit/23695cbdc4ff1b9fa58c18d4a3c2f18e21451b8b 但是，他们在Rails 3.1.0上发布了。

对于Rails 3.1.0，创建Rails.root / initializers / kaminari_for_distinct.rb。并使用以下代码。

module Kaminari
  module ActiveRecordRelationMethods
    extend ActiveSupport::Concern
    module InstanceMethods
      def total_count #:nodoc:
        if distinct_column_name.nil?
          c = except(:offset, :limit).count
        else  
          c = except(:offset, :limit).count(distinct_column_name, :distinct => true)
        end
        # .group returns an OrderdHash that responds to #count
        c.respond_to?(:count) ? c.count : c
      end

      # Get the column name used in distinct query.
      # This could have been set on the Model class, or the ActiveRecord::Relation 
      def distinct_column_name
        @distinct_column || distinct_column
      end
    end
  end
end

module Kaminari
  module ConfigurationMethods
    extend ActiveSupport::Concern
    module ClassMethods

      # Set the name of the column to use during .count()
      # Setting this will cause call to count to use: count(:id, :distinct => true) for all the Models paged queries. 
      # Example:
      #   class User < ActiveRecord::Base
      #     use_distinct :id
      #   end
      def use_distinct(column)
        @distinct_column = column
      end

      # Returns the distinct column name set on the Model, or nil if not using distinct
      def distinct_column
        @distinct_column
      end
    end
  end
end


module Kaminari
  module PageScopeMethods
    extend ActiveSupport::Concern
    module InstanceMethods

      # Set the name of the column to use during .count()
      # Setting this will cause call to count to use: count(:id, :distinct => true)
      # Example: User.page(3).per(5).use_distinct(:id)
      def use_distinct(column)
        @distinct_column = column
        self
      end
    end
  end
end

Answer 2

我建议在模型上使用范围

这可能会让事情变得混乱，所以你要小心

范围：count，select（“DISTINCT things。*”）

有关详细信息，请查看here

强制ActiveRecord计数不同（使用Kaminari）

2 个答案: