使用ActiveRecord将Afcolumn乘以Rails的值 [英] Rails Multiplying value of afcolumn using ActiveRecord

问题描述

我要考虑用户ID乘以特定列的值。

I want to multiply a value of an specific column considering the user id.

假设我有一个表 users ，其中包含用户1（id 1）和用户2（id 2），以及具有名称的表动物和 mensal_cost 。

Assume I have a table users with user 1 (id 1) and user 2 (id 2), and a table animals which has name and mensal_cost.

好，然后我为用户1（id 1）添加了两个动物，为用户1添加了动物2（id 2）

Ok, then I added two animals for user 1 (id 1) and 1 animal for user 2 (id 2)

我想知道如何使用 ActiveRecord 计算 mensal_cost 3个月后增加相同的基本值，这意味着我必须将实际值乘以3。

I want to know how I can using ActiveRecord calculates the mensal_cost income after 3 months increasing the same base value, it means I have to multiply the actual value by 3.

我正在尝试某些方法像这样：

I'm trying something like this:

Animal.where(user_id: ?).sum('3*mensal_cost') 

由于我不知道可以存在多少个用户，因此我必须写一个电话，该电话将为每个用户ID列出之后的金额3个月。

Since I don't know how many users can exist, I must write a call which will list for each user id the amount after 3 months.

推荐答案

好吧，您几乎自己拥有了它-只是一些小细节可以像这样：

Ok, you nearly had it on your own - just the minor details can be like this:

user_ids = [id1, id2]
full_sum = 3 * Animal.where(:user_id => user_ids).sum(:mensal_cost)

注意：请记住，求和后可以乘以三等于将每个数字乘以3，例如

Note: don't forget you can multiply by three after summing and it'll be the same as summing each one multiplied by 3 eg

（3 * 2）+（3 * 3）+（3 * 4）== 3 *（2 + 3 + 4）

(3 * 2) + (3 * 3) + (3 * 4) == 3 * (2 + 3 + 4)

或您可以遍历用户以获取其个人总和，如下所示：

or you can iterate through the users to get their individual sums like so:

mensal_sums = {}
user_ids = [id1, id2]
user_ids.each do |user_id|
   mensal_sums[user_id] = 3 * Animal.where(:user_id => user_id).sum(:mensal_cost)
end

puts mensal_sums
=> {id1 => 63, id2 => 27}

编辑
以及您想要用户名的位置：

EDIT and one where you want the user name as well:

mensal_sums = {}
users = User.find([id1, id2])
users.each do |user|
   mensal_sums[user.id] = {:user_name => user.name,
                           :sum => (3 * user.animals.sum(:mensal_cost)) }
end

puts mensal_sums
=> {id1 => {:user_name => "Bob Jones", :sum => 63},
    id2 => {:user_name => "cJane Brown", :sum =>27}
   }

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