Question

I have an ActiveRecord model that has two database attributes, total and processing_fees.

It has various scopes defined, such as (just as examples):

class Item < ActiveRecord::Base
  scope :completed, joins(:order).where(:orders => {:status => Order::Status::COMPLETED})
  scope :for_client, lambda {|client| where("client_id=?", client.id)}
...etc...
end

I can easily do something like:

Item.completed.for_client(client).sum(:total)

but what I would like to do is something like:

Item.completed.for_client(client).calculate(:total - :processing_fees) # obv not valid

Is there any way to do such a thing?

Answer 1

Something like this should work:

Item.completed.for_client(client).calculate(:sum, "item.total - item.processing_fees")