Ruby on Rails: how to get error messages from a child resource displayed?

Question

I\'m having a difficult time understanding how to get Rails to show an explicit error message for a child resource that is failing validation when I render an XML template.

Answer 1

Update Rails 5.0.1

You can use Active Record Autosave Association

class School < ActiveRecord::Base
    has_many :students, autosave: true
    validates_associated :students
end

class Student < ActiveRecord::Base
    belongs_to :school
    validates_format_of :email,
                  :with => /^([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})$/i,
                  :message => "You must supply a valid email"
end

@school = School.new
@school.build_student(email: 'xyz')
@school.save
@school.errors.full_messages ==> ['You must supply a valid email']

reference: http://api.rubyonrails.org/classes/ActiveRecord/AutosaveAssociation.html