Rails Group data and render as json

I have a User model with many coupons. Each coupon has a value.

I would like to retrieve some data about all the user coupons, like the sum of the value of all the coupons for each开发者_StackOverflow user. I also would like to group data by day.

How can I do this?

There is a method called sum that can be used on the associations. For example:

@user.coupons.all.sum(&:value)

In this case value is the attribute you want to sum.

And to group these by date, then perhaps something like this:

#group_by will create a hash with the dates as keys and place the coupons in arrays
@coupons = @user.coupons.all.group_by{ |coupon| coupon.created_at.strftime("%D") }

#Loop through all keys (dates) and get the sum of the coupons
@coupons.keys.each |date|
  puts "Date: #{date}, Value: #{@coupons[date].sum(&:value)}"
end