Rails中ActiveRecord中的多个sum()

Question

我想在同时选择其他字段时将多个sums()链接到一个组.我也更喜欢使用ActiveRecord方法来做这个而不是手动构造一个sql字符串,因为我可以稍后修改ActiveRecord的继承类的行为.

例如,我想代表声明(作为例子)

select user_id, sum(cost) as total_cost, sum(quantity) as total_quantity from line_items group by user_id

有类似的东西:

LineItem.select(:user_id).group(:user_id).sum(:cost).sum(:quantity)

原因是我可能会在以后添加额外的分组和where子句,所有的总和将具有共同点.

Answer 1

这对我有用:

require "active_record"
require "logger"

ActiveRecord::Base.logger = Logger.new(STDOUT)
ActiveRecord::Base.establish_connection :adapter => "postgresql", :database => "francois"

ActiveRecord::Base.connection.execute "DROP TABLE IF EXISTS values"
ActiveRecord::Base.connection.execute "CREATE TABLE values(user_id INTEGER NOT NULL, quantity INTEGER NOT NULL DEFAULT 1, cost INTEGER NOT NULL DEFAULT 2)"

class Value < ActiveRecord::Base
end

2.times do
  5.times do |n|
    Value.create!(:user_id => n)
  end
end

Value.group(:user_id).select('user_id, SUM(cost) AS total_cost, SUM(quantity) AS total_quantity').each do |value|
  p [value.user_id, value.total_quantity, value.total_cost]
end

我尝试过sum(:cost, :quantity),但#sum不要指望以这种方式定义参数.我也试过sum(:cost => :total_cost, :quantity => :total_quantity),无济于事.