从范围记录计算总数百分比并显示虚拟属性（Rails / Active Record）
创建一个范围，可能是这样的..
scope :mv, select('*,quantity*market_price as market_value, quantity*market_price/sum(quantity*market_price) as percent') 这会创建两个虚拟属性，market_value和percent。 我遇到的问题是创建包含sum（）的百分比。 如果我添加sum（），则范围返回一条记录。
我需要计算相对于范围记录集的总市值的market_value的百分比。
例：
1, market_value: 100, percent: .10 2, market_value: 100, percent: .10 3, market_value: 100, percent: .10 4, market_value: 100, percent: .10 5, market_value: 100, percent: .10 6, market_value: 500, percent: .50 Total is 1000
但是，如果我将其范围扩大到market_value <6，我应该看到
1, market_value: 100, percent: .20 2, market_value: 100, percent: .20 3, market_value: 100, percent: .20 4, market_value: 100, percent: .20 5, market_value: 100, percent: .20 Total 500
我怎么能做到这一点？
我创建了一个self.pct方法，但self.pct方法的问题是它需要在所有范围之后运行。 如果重新调整，解决方案是错误的
至今，
class Position 'L') scope :short_only, where(:account_type=>"S") scope :equity_only, :conditions => ["symbol 'USD'"] scope :mv, select('*,quantity*market_price as market_value, quantity*market_price/sum(quantity*market_price) as percent') scope :mv1, lambda{|total| select(total) } #the problem with the self.pct method is that it needs to be run after all the scopes. if rescoped, the solution is wrong def self.pct string="*,(quantity*market_price) as market_value, (market_price*quantity/#{sum_market_value}) as percent" mv1(string) end def market_value self.market_price*self.quantity end def self.sum_market_value sum('quantity*market_price') end end
我不知道是否有办法在单个查询中执行此操作，但我们可以在两个查询中获取它：
require 'active_record' ActiveRecord::Base.establish_connection adapter: 'sqlite3', database: ':memory:' ActiveRecord::Schema.define do self.verbose = false create_table :positions do |t| t.integer :quantity t.integer :market_price end end class Position < ActiveRecord::Base def self.with_market_value select "*, quantity*market_price as market_value, quantity*market_price/#{total.to_f} as percent" end def self.total select('sum(quantity*market_price) as sum_of_market_values').first.sum_of_market_values end end Position.create! quantity: 25, market_price: 4 Position.create! quantity: 25, market_price: 4 Position.create! quantity: 25, market_price: 4 Position.create! quantity: 25, market_price: 4 Position.create! quantity: 25, market_price: 4 Position.create! quantity: 25, market_price: 20 Position.with_market_value.map { |p| [p.market_value, p.percent] } # => [[100, 0.1], [100, 0.1], [100, 0.1], [100, 0.1], [100, 0.1], [500, 0.5]] Position.where('market_price < 10').with_market_value.map { |p| [p.market_value, p.percent] } # => [[100, 0.2], [100, 0.2], [100, 0.2], [100, 0.2], [100, 0.2]] # ** NOTE THAT IT EXECUTES EAGERLY ** Position.with_market_value.where('market_price < 10').map { |p| [p.market_value, p.percent] } # => [[100, 0.1], [100, 0.1], [100, 0.1], [100, 0.1], [100, 0.1]]