ruby-on-rails – 在Rails上使用计算进行组查询3

Rails 3问题.
我有一份Foods食品表,其中包含以下属性：

>名字
>卡路里(每克)
>脂肪(每克)
>碳水化合物(每克)
>蛋白质(每克)

然后我有一个LoggedFoods表,表示在给定时间吃过的食物.它具有以下属性：

> food_id
> number_of_grams_eaten
> ate_when(datetime)

所以我的问题是我想在一次查询中得到每天(所有日子)消耗的卡路里,脂肪,蛋白质,碳水化合物的总数.我一直在尝试使用新的ActiveRecord查询界面执行此Rails 3并且没有运气.有任何想法吗？

解决方法

这是一个快速的第一步,可能有一些错误,但数字似乎一目了然.另外：我只在sqlite3上测试过,所以其他数据库的结果可能不同(如果SUM或组函数不同)

应用程序/模型/ logged_food.rb

class LoggedFood < ActiveRecord::Base
  belongs_to :food

  def self.totals_by_day(date)
    start_time = Time.parse(date).beginning_of_day
    end_time = Time.parse(date).end_of_day

    t = LoggedFood.arel_table

    totals = LoggedFood.
      where(t[:ate_when].gteq(start_time)).
      where(t[:ate_when].lteq(end_time)).
      joins(:food).
      select("SUM(calories * grams_eaten) as total_calories").
      select("SUM(fat * grams_eaten) as total_fat").
      select("SUM(carbs * grams_eaten) as total_carbs").
      select("SUM(protien * grams_eaten) as total_protien")

    return nil if totals.empty?

    {
      :total_calories => totals.first.total_calories,:total_fat => totals.first.total_fat,:total_carbs => totals.first.total_carbs,:total_protien => totals.first.total_protien
    }

  end

end

db / seeds.rb(我显然不知道食物的营养信息)

@pizza = Food.create(:name => "pizza",:calories => 500,:fat => 10,:carbs => 20,:protien => 30)
@hot_dog = Food.create(:name => "hot dog",:calories => 400,:protien => 30)
@apple = Food.create(:name => "apple",:calories => 100,:fat => 1,:carbs => 2,:protien => 3)
@banana = Food.create(:name => "banana",:fat => 2,:carbs => 4,:protien => 6)

LoggedFood.create(:food_id => @pizza.id,:grams_eaten => 10,:ate_when => Time.Now)
LoggedFood.create(:food_id => @apple.id,:ate_when => Time.Now)
LoggedFood.create(:food_id => @banana.id,:ate_when => 12.hours.ago)
LoggedFood.create(:food_id => @apple.id,:ate_when => 1.day.ago)
LoggedFood.create(:food_id => @pizza.id,:ate_when => 2.days.ago)
LoggedFood.create(:food_id => @banana.id,:ate_when => 36.hours.ago)
LoggedFood.create(:food_id => @hot_dog.id,:ate_when => 50.hours.ago)

然后在控制台中：

ree-1.8.7-2010.02 > LoggedFood.totals_by_day("2010-08-27")
  LoggedFood Load (0.2ms)  SELECT SUM(calories * grams_eaten) as total_calories,SUM(fat * grams_eaten) as total_fat,SUM(carbs * grams_eaten) as total_carbs,SUM(protien * grams_eaten) as total_protien FROM "logged_foods" INNER JOIN "foods" ON "foods"."id" = "logged_foods"."food_id" WHERE ("logged_foods"."ate_when" >= '2010-08-27 04:00:00.000000') AND ("logged_foods"."ate_when" <= '2010-08-28 03:59:59.999999') LIMIT 1
 => {:total_fat=>130,:total_protien=>390,:total_calories=>7000,:total_carbs=>260} 

ree-1.8.7-2010.02 > LoggedFood.totals_by_day("2010-08-26")
  LoggedFood Load (0.3ms)  SELECT SUM(calories * grams_eaten) as total_calories,SUM(protien * grams_eaten) as total_protien FROM "logged_foods" INNER JOIN "foods" ON "foods"."id" = "logged_foods"."food_id" WHERE ("logged_foods"."ate_when" >= '2010-08-26 04:00:00.000000') AND ("logged_foods"."ate_when" <= '2010-08-27 03:59:59.999999') LIMIT 1
 => {:total_fat=>30,:total_protien=>90,:total_calories=>2000,:total_carbs=>60}