Considering an object with several has_many :through => associations, what is the 'best' way to handle validations?
As an example:
class Student < ActiveRecord::Base
# some attrbutes like # :name # :grade
has_many :students_assignment, :dependent => :destroy has_many :assignments, :through => :students_assignment
has_many :students_class, :dependent => :destroy has_many :classes, :through => :students_class
has_many :students_extracurricular_activity, :dependent => :destroy has_many :extracurricular_activities, :through => :students_extracurricular_activity
has_many :students_school, :dependent => :destroy has_many :students_schools, :through => :students_school
Suppose a student can't belong to a class and extracurricular activity that occur at the same time? I figure that this validation would be best handled in the Student class since the other case would require writing validations for both classes and eca's. Also, this is just an example. So, what if a student also can only take a :class through multiple :schools if they are of a certain :grade and only 5 students can belong to each eca?
I'm trying to illustrate a complex situation where the combination of multiple associations affect the validity. So either each association has to be validated, which means processing for the most part the same validations for all associations. For instance, checking a students eca's against the students classes (for timing conflicts) would be done twice, once from eca's and again from classes. i would like to handle this through a validates_associated so that the Student is validated whenever an association is changed or added. However, I can't see how this would work.
ss = StudentsSchool.new(:school_id => 1, :student_id => 10)
So the ss is still a temporary object that won't be seen in the Student validation.
Can anyone share some ideas?