ActionController::UrlGenerationError in Comments#show - ruby-on-rails

Question

I use polymorphic associations with comments. When I try to add 'edit' and also 'destroy' in show template, I get the error in the title (just edit for now). How do I add both links to show?
comments_controller.rb
class CommentsController < ApplicationController
....
before_action :signed_in_user, only: [:new, :edit]
before_filter :load_commentable
def index
#commentable = load_commentable
#comments = #commentable.comments
end
def show
end
def edit
#commentable = load_commentable
end
def new
#commentable = load_commentable
#comment = #commentable.comments.new
end
def create
#comment = #commentable.comments.new(comment_params)
#comment.user = current_user
if #comment.save
redirect_to #comment, notice: "Created."
else
render :new
end
end
def update
#comment = #commentable.comments.build(comment_params)
#comment.user = current_user
respond_to do |format|
if #comment.update(comment_params)
format.html { redirect_to #comment, notice: 'It was successfully updated.' }
format.json { head :no_content }
else
format.html { render action: 'edit' }
format.json { render json: #comment.errors, status: :unprocessable_entity }
end
end
end
private
def load_commentable
resource, id = request.path.split('/')[1, 2]
#commentable = resource.singularize.classify.constantize.find(id)
end
....
end
show.html.erb template
<%= link_to "Edit", [:edit, #commentable, :comment] %>
form
<%= form_for [#commentable, #comment] do |f| %>
....
full trace
log
Processing by CommentsController#show as HTML
Parameters: {"post_id"=>"1", "id"=>"2"}
Comment Load (0.3ms) SELECT "comments".* FROM "comments" WHERE
"comments"."id" = ? LIMIT 1 [["id", "2"]]
Post Load (0.2ms) SELECT "posts".* FROM "posts" WHERE "posts"."id" =
? LIMIT 1 [["id", "1"]]
User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."id" =
? ORDER BY "users"."id" ASC LIMIT 1 [["id", 2]]
(0.2ms) SELECT COUNT(*) FROM "comments" WHERE "comments"."user_id" =
? [["user_id", 2]] CACHE (0.0ms) SELECT COUNT(*) FROM "comments"
WHERE "comments"."user_id" = ? [["user_id", 2]]
Rendered comments/show.html.erb within layouts/application (10.7ms)
Completed 500 Internal Server Error in 19ms
ActionView::Template::Error (No route matches {:action=>"edit",
:controller=>"comments", :post_id=>#, :id=>nil,
:format=>nil} missing required keys: [:id]):
25: <div class="thumbsdown"><%= link_to image_tag('othericons/thumbiconDown.PNG', height: '20', width: '20'),
"#" %>
26: <%= link_to image_tag('othericons/flagicon.PNG', height: '20', width: '18'), "#"
%>
27:
28: <%= link_to "Edit", [:edit, #commentable, :comment] %> 29:
30:
31: app/views/comments/show.html.erb:28:in
`_app_views_comments_show_html_erb___2937579164590753686_69833853514120'
Rendered /home/action/.rvm/gems/ruby-2.0.0-p247/gems/actionpack-4.0.0/lib/action_dispatch/middleware/templates/rescues/_trace.erb
(1.6ms) Rendered
/home/action/.rvm/gems/ruby-2.0.0-p247/gems/actionpack-4.0.0/lib/action_dispatch/middleware/templates/rescues/_request_and_response.erb
(1.2ms) Rendered
/home/action/.rvm/gems/ruby-2.0.0-p247/gems/actionpack-4.0.0/lib/action_dispatch/middleware/templates/rescues/template_error.erb
within rescues/layout (19.1ms)
routes:
resources :posts do
resources :comments
end

Answer 1

Change the Edit Link as below:
<%= link_to "Edit", edit_post_comment_path(#commentable, #comment) %>
You have setup Post and Comment as nested routes, so you need to pass objects of Post as well as Comment to the edit path.
EDIT
For Polymorphic association, you could use it as below:
<%= link_to "Edit", [:edit, #commentable, #comment] %>