Ruby-on-rails Rails 如何对列求和？

Rails how to sum columns?

提问by Rails beginner

Example I have:

我有的例子：

@test = Pakke.find([[4], [5]])

In my Pakke table I have a column named prismd

在我的 Pakke 表中，我有一列名为 prismd

How do I sum the two values for the prismdcolumns for @test?

如何prismd对@test的列的两个值求和？

回答by Holger Just

You can summarize directly on the database by creating the respective SQL like this:

您可以通过创建相应的 SQL 来直接在数据库上进行汇总，如下所示：

Pakke.sum(:prismd, :conditions => {:id => [4,5]})

See ActiveRecord::Calculationsfor more usage examples and general documentation.

有关更多使用示例和一般文档，请参阅ActiveRecord::Calculations。

回答by Jordan Running

ActiveRecord has a bunch of built-in calculation methods, including sum:

ActiveRecord 有一堆内置的计算方法，包括sum：

@test = Pakke.where(:id => [4, 5] ).sum(:prismd)

回答by Rails beginner

Pakke.find([[14], [15]]).map(&:prismd).sum

回答by KevinLi

test = Order.where(potential_student_id: potential_student.id).sum("total_price");

test = Order.where(potential_student_id: potential_student.id).sum("total_price");