Question

I have several hundred documents with this information:

=> User(id: integer, email: string, amount: string)

How can I sum the amount variable of all the documents?

I am using Rails + Mongoid.

thanks

Answer 1

Normally with an integer field, you could do this:

User.sum(:amount)
# => 142.0

However, since your amount field is a string, it’ll just concatenate strings instead. For example, if you had 3 users with amounts of 12, 30, and 100, you would get “01230100” as a result. In this case, you may need to use something like Ruby’s inject instead:

User.all.inject(0) { |sum, user| sum + user.amount.to_f }
# => 142.0