Model Validation Messages Rails 4 form errors not showing up - ruby-on-rails

Question

I have a form which allows a user to invite multiple people via adding emails in a comma separated list. In my "Participant" model, I have a call to validate the uniqueness of the email entered (scoped by "project_id"). In the model validation, it gives a place to explain the error (message), but I can't get that error to show up on my form if the validation fails.
If a user enters the email of a person that has already been added, how can I get the errors message to render?
participant.rb
class Participant < ActiveRecord::Base
validates :email, uniqueness: {case_sensitive: false, scope: :project_id, message: "Looks like you\'ve already added this person."}
end
participant_controller.rb
def new_participant
#new_participants = Participant.new
#participants = Participant.where(project_id: #project.id).includes(:user)
#template = Template.find(#project.template_id)
#address = Address.where(project_id: #project.id).first
#food = ProjectRestriction.where(project_id: #project.id)
end
def add_participant
#added_by = User.find(current_user.id)
#new_participants = params[:new_participants][:email].split(/,\s*/)
#new_participants.each do |t|
newpart = Participant.new(:email => t, :project_id => #project.id, :level => 4,
:participant_cat_id => 2, :last_updated_by => current_user.id, :added_by => current_user.id, :status => 'unseen')
respond_to do |format|
if newpart.save
ProjectMailer.notify_recipient(newpart, #project, #added_by, #participant_invite ).deliver_later
self.response_body = nil
redirect_to participants_path(p: #project.id, w: 'recipient')
else
format.html { redirect_to new_participant_path(p: #project.id)}
format.json { render json: #new_participants.errors, status: :unprocessable_entity }
end
end
end
end
form
<%= form_for :new_participants, url: add_participant_path( :p => #project.id), html: { :multipart => true, :class=> "form-horizontal", id: "basicForm" } do |f| %>
<% if #new_participants.errors.any? %>
<h2>OOPS!</h2>
<ul>
<% #new_participants.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul></div>
<% end %>
<div class="form-group ">
<label class="form-label dk-aqua"> Email: <span class="asterisk">*</span></label>
<%= f.text_field :email, :autofocus => true, :required => true, :maxlength => 55, :placeholder => 'Email(s)', :class => 'form-control' %>
</div>
<%= f.submit 'INVITE', :class => 'btn btn-aqua btn-lg btn-block',
:style => 'margin-bottom:-5px' %>
<% end %>

Answer 1

Your main issues are:
you are creating a respond block for each email in the request. 1 request = 1 response.
The objects in stored in memory in #new_participants are not actually saved.
In your views your are treating #new_participants as if it where a single resource.
Pay attention to pluralization when naming routes, variables and actions.
def add_participants
#added_by = User.find(current_user.id)
#new_participants = params[:new_participants][:email].split(/,\s*/)
#new_participants.map do |email|
newpart = Participant.new(
:email => email,
:project_id => #project.id,
:level => 4,
:participant_cat_id => 2,
:last_updated_by => current_user.id,
:added_by => current_user.id,
:status => 'unseen'
)
if newpart.save
ProjectMailer.notify_recipient(newpart, #project, #added_by, #participant_invite ).deliver_later
end
new_part
end
#invalid = #new_participants.reject(&:valid?)
if #invalid.any?
respond_to do |format|
format.html { redirect_to new_participant_path(p: #project.id)}
format.json { render json: #new_participants.map(&:errors), status: :unprocessable_entity }
end
else
respond_to do |format|
redirect_to participants_path(p: #project.id, w: 'recipient')
end
end
end
<ul>
<% #new_participants.each |p| %>
<% p.errors.messages.each do |msg| %>
<li><%= msg %></li>
<% end if p.errors.any? %>
<% end %>
</ul>