collections.rb

resources :collections do
  resources :notes, :tags
end

def new
  @ticket = @project.tickets.build
end
# is basically the same as 
def new
  @ticket = Ticket.new(project_id: @project.id)
end

# setting @project and @ticket
# note @project is set before @ticket
before_filter :set_project
before_filter :set_ticket, only: [:show, :edit, :update, :destroy]

private
  def set_project
    @project = Project.find(params[:project_id])
  end

  def set_ticket
    @ticket = @project.tickets.find(params[:id])
  end

# note, if you're using the before_filter as an authorization technique,
# you're going to have to decide how to handle ActiveRecord::RecordNotFound
# exceptions when a non-existent Collection, Note, or Tag is requested
# search "ActiveRecord::RecordNotFound" in Rails 4 in Action
# discussion of handling the exception in 4.4 and on as well as 8.4 and on
# here's one approach, see p132
private
  def set_project
    @project = Project.find(params[:id])
  rescue ActiveRecord::RecordNotFound
    flash[:alert] = "The project you were looking" +
                    " for could not be found."
    redirect_to projects_path
  end

# forms for nested resources
# note the use of @project and @ticket instead of simply @ticket
= form_for [@project, @ticket] do |f|

# spec references
# see p137 for "creating ticket" spec
# see p152 for "viewing tickets" spec. note that two separate projects are created. note use of 'within' in the spec

# note the use of [@project, @ticket] array when creating links
# avoid some_path_to_path stuff. 
<ul id='tickets'>
  <% @project.tickets.each do |ticket| %>
    <li>
      #<%= ticket.id %> -
      <%= link_to ticket.title, [@project, ticket] %>
    </li>
  <% end %>
</ul>

# Seed data, check out section 8.9.3