ActiveRecord查询模型上不存在字段的位置

Question

I have a bit of a complex query I'm trying to write.

I want to find all Order s that have a negative balance, but balance isn't a field on Order it's a method in the Order class that calls three other methods that call other methods, and by the end, about 5 classes are called, making doing this in SQL or writing a long AR query very difficult.

Is there a way to get the result without pulling the records and looping over them, and without reimplementing each method that builds the order balance?

For reference, I'm doing it like this right now:

    negative_balances = []
    Order.find_each {|o| negative_balances << o if o.balance > 0}
    @negative_balances = negative_balances.group_by {|o| o.created_at.to_date}

and balance looks like this:

class Order < AR::Base
  def balance
    total - (charge_payment + credit_payment)
  end
end

Answer 1

You can do addition and subtraction in SQL. Assuming total , charge_payment , and credit_payment are all integer columns on the orders table, then:

Order.where("(total - (charge_payment + credit_payment)) < 0")