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

This is not a public API yet, but Rails 5 stable seems to have ActiveModel::Errors#copy! to merge errors between two models.

user  = User.new(name: "foo", email: nil)
other = User.new(name: nil, email:"foo@bar.com")

user.errors.copy!(other.errors)
user.full_messages #=> [ "name is blank", "email is blank" ] 

Again, this is not officially published yet (I accidentally find this one before monkey-patching Errors class), and I'm not sure it will be.

So it's up to you.

Answer 2

You should use following in the rhtml.

<%= error_messages_for :school, :student %>

To skip "Students is invalid" message use following in the student.rb

  def after_validation
    # Skip errors that won't be useful to the end user
    filtered_errors = self.errors.reject{ |err| %w{ student}.include?(err.first) }
    self.errors.clear
    filtered_errors.each { |err| self.errors.add(*err) }
  end

EDITED

Sorry after_validation must be in a school.rb