fields_for not creating a record when making a new parent record

Question

I am trying to automatically create a child record (Participant) when I create a parent (Project) record. I can create the parent (Project) fine and, on other forms, I can create the child (Participant). I cannot seem to create the child (Participant) at the same time as the parent.

I am on Rails 4, and so I've set my strong params carefully. I just don't understand what I'm doing wrong.

Parent Controller:

class ProjectsController < ApplicationController

  def new_project
    @title = params[:ti]
    @project = Project.new  
    @project.participants.build
  end


def create_project
  @project = Project.new(project_params)
  @template = Template.find(params[:t]) 
   @project.participants.build
   @title = params[:ti]
  respond_to do |format|
     if @project.save
        @project.participants.save
        format.html { redirect_to new_milestones_path(:p => @project.id), notice: 'Great! We saved your project details.' }
      else
        format.html {   redirect_to  new_project_path(t: @template.id, ti: @title)         
 }
        format.json { render json: @project.errors, status: :unprocessable_entity }
      end
    end
  end

  def project_params
    params.require(:project).permit( :id, :title, :starts, participants_attributes: [:id, :email, :title, :status, :project_id])
  end
end

Models:

 class Participant < ActiveRecord::Base
   belongs_to :project, inverse_of: :participants
   ........
 end

 class Project < ActiveRecord::Base
   has_many :participants, dependent: :destroy, inverse_of: :project
   accepts_nested_attributes_for :participants, allow_destroy: true, reject_if: proc { |a| a["email"].blank? }
   .........
 end

Form:

 <%= form_for @project, url: create_project_path(ti: @title), html: { :multipart => true, :class=> "form-horizontal", id: "basicForm" }do |f| %> 

   <%= f.fields_for :participants do |ff|%>

     <%= ff.hidden_field :email, :value => current_user.email %>
     <%= ff.hidden_field :title, :value => 'Organizer' %>
     <%= ff.hidden_field :status, :value => 'accepted' %>

   <% end %> 
   <%=  f.text_field  :title, :placeholder => 'Your Project Title'%>
   <%=  f.text_field  :starts, :placeholder => 'mm/dd/yyyy'%>

   <%= f.submit ' SAVE PROJECT' %>  
 <% end %>

UPDATE: I added @project.participants.build as Samo suggested (and I've updated my code above), which makes the fields_for visible...but my project doesn't save...it redirects back to new_project_path.

Answer 1

I believe I see the issue. In your new_project action, try this:

  def new_project
    @title = params[:ti]
    @project = Project.new  
    @project.participants.build
  end

To elaborate: fields_for is not going to render anything if the association is blank/empty. You need to have at least one participant returned by @project.participants in order to see its fields. @project.participants.build will simply insert a new instance of the Participant class into the association.