ruby on rails - Checking Expense amount and expense type maximum cap -

i'm trying build small expense tracking app using rails 4.1. there expense_types model expense_name , cap. used set maximum caps gas, mobile etc. claims. expense types belong expenses model users submit. in new expense form, pick expense type drop down , add line items.

i use model method calculate total of line items. now, i'd check after every submission if total amount exceeds expense type cap. expense type stored each submission. example, if gas (expense_type_id = 2) bill submitted $100 , cap $80 i'd update notification attribute.

i'm bit confused how correctly. tried following method, got undefined method expense_type error:

def check_cap     if self.expense_amount.to_i != self.expense_type.cap         self.update_attribute(:notification, "this item on budget")     end end  

wondering how use expense_type_id check condition can me out?

your expense_type association backwards. expense should belong_to expense_type, not other way around.

use activerecord validations , errors indicate amount on cap. way record not valid , not save until valid.

check expense_amount greater cap. checking not equal mark item on budget time expense amount higher or lower cap.

class expensetype < activerecord::base   has_many :expenses end  class expense < activerecord::base   belongs_to :expense_type    validate :expense_amount_is_within_cap    def expense_amount_is_within_cap      if expense_amount > expense_type.cap       errors.add(:expense_amount, 'is on budget')     end   end end