问如何操作form_for来改变将params[]发送到控制器的方式？

EN

<%= form_for @registration, method: :post do |form| %>
    <div class="form form-actions">
      <%= form.hidden_field :occurrence_id, :value => @occurrence.id %>
      <%= submit_tag "Yes, register", class: 'btn btn-primary' %>
      <%=  link_to "Cancel", root_path, class: 'btn' %>
    </div>
<% end %>

def create
  if params[:occurrence_id]
    @occurrence = Occurrence.find(params[:occurrence_id])
    @registration = Registration.new(registration_date: Date.today, user: current_user, occurrence: @occurrence)
    if @registration.save
      flash[:success] = "Course registration saved with success."
    else
      flash[:error] = "There was a problem saving the registration."
    end
    redirect_to occurrence_path(@occurrence)
  else
    flash[:error] = "Occurrence missing"
    redirect_to root_path
  end
end

{"utf8"=>"✓",
 "authenticity_token"=>"5RFiAq3DiqauNzSpnXIcPzWEl9UuGqoXfYAvRiB6GKk=",
 "registration"=>{"occurrence_id"=>"2"},
 "commit"=>"Yes,
 register"}

{"utf8"=>"✓",
 "authenticity_token"=>"5RFiAq3DiqauNzSpnXIcPzWEl9UuGqoXfYAvRiB6GKk=",
 "occurrence_id"=> "2",
 "commit"=>"Yes,
 register"}