Require nine-digit ID numbers

Avoids issue #1.

Author: maxg

app/models/student.rb

@@ -5,6 +5,7 @@ class Student < ActiveRecord::Base
 
   validates_presence_of :_student_first_name, :_student_last_name, :_student_id_number
   validates_inclusion_of :_student_gender, :in => [ 'Male', 'Female' ]
+  validates_length_of :_student_id_number, :is => 9
   validates_uniqueness_of :_student_id_number
   validates_numericality_of :_student_id_number
   validates_format_of :_student_email, :with => /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/i

config/locales/student.yml

@@ -48,6 +48,8 @@ en:
       models:
         student:
           attributes:
+            _student_id_number:
+              wrong_length: should be %{count} digits long
             _student_gender:
               inclusion: can't be blank
             _student_city: