Rails polymorphic posts associations and form_for in views - ruby-on-rails

Question

I've been having trouble setting up the form for a polymorphic "department" post in the department view. I followed the rails-cast tutorial for polymorphic associations here
Models:
class Course < ActiveRecord::Base
belongs_to :department, inverse_of: :courses
has_and_belongs_to_many :users, -> { uniq }
has_many :posts, as: :postable #allows polymorphic posts
end
class Department < ActiveRecord::Base
has_many :courses, inverse_of: :department
has_many :posts, as: :postable #allows polymorphic posts
has_and_belongs_to_many :users, -> {uniq}
end
class Post < ActiveRecord::Base
belongs_to :user, touch: true #updates the updated_at timestamp whenever post is saved
belongs_to :postable, polymorphic: true #http://guides.rubyonrails.org/association_basics.html#polymorphic-associations
belongs_to :department, counter_cache: true #for counting number of posts in department
belongs_to :course, counter_cache: true
validates :department_id, :course_id, presence: true
end
config/routes
devise_for :users
devise_scope :users do
match '/users/:id', to: "users#show", via: 'get'
end
resources :departments do
resources :courses
resources :posts
end
resources :courses do
resources :posts
end
views/departments/show.html.erb
<div class="tab-pane" id="posts"><br>
<center><h3>Posts:</h3></center>
<%= render "posts/form", postable: #department %>
</div>
views/posts/_form.html.erb
<%= render "posts/wysihtml5" %>
<center><h3>Create New Post:</h3></center>
<%= form_for [#postable, Post.new] do |f| %>
<%= f.label :title %>
<%= f.text_field :title, class: "form-control" %>
<%= f.label :description %>
<%= f.text_area :description, :rows => 3, class: "form-control" %>
<%= f.text_area :content, :rows => 5, placeholder: 'Enter Content Here', class: "wysihtml5" %>
<span class="pull-left"><%= f.submit "Create Post", class: "btn btn-medium btn-primary" %></span>
<% end %>
controllers/post_controller.rb
class PostsController < ApplicationController
before_filter :find_postable
load_and_authorize_resource
def new
#postable = find_postable
#post = #postable.posts.new
end
def create
#postable = find_postable
#post = #postable.posts.build(post_params)
if #post.save
flash[:success] = "#{#post.title} was sucessfully created!"
redirect_to department_post_path#id: nil #redirects back to the current index action
else
render action: 'new'
end
end
def show
#post = Post.find(params[:id])
end
def index
#postable = find_postable
#posts = #postable.posts
end
...
private
def post_params
params.require(:post).permit(:title, :description, :content)
end
def find_postable #gets the type of post to create
params.each do |name, value|
if name =~ /(.+)_id$/
return $1.classify.constantize.find(value)
end
end
nil
end
controllers/departments_controller.rb
def show
id = params[:id]
#department = Department.find(id)
#course = Course.new
#course.department_id = #department
end
The error is "undefined method `posts_path' for #<#:0x0000010d1dab10>"
I think the error has something to do with the path in the form, but I don't know what. I've tried [#postable, #postable.posts.build] as well but that just gives me undefined method: PostsController.
Anybody know what's going on and how I can fix it?

Answer 1

#department is passed into the form partial as a local variable, but the form calls an instance variable:
# views/departments/show.html.erb
<%= render "posts/form", postable: #department %> # <------ postable
# views/posts/_form.html.erb
<%= form_for [#postable, Post.new] do |f| %> # <------ #postable
Thus, the namespaced route is not properly determined
[#postable, Post.new] # => departments_posts_path
[ nil , Post.new] # => posts_path
Checking your routes, posts are only accessible via nested routes. posts_path is not a valid route, it's method does not exist, and the error is correct: undefined method `posts_path'
Fix:
Set a #postable instance variable in the departments controller so that the form helper can use it:
def show
id = params[:id]
#postable, #department = Department.find(id) # <-- add #postable
#course = Course.new
#course.department_id = #department
end
Then you can simply call render in the view:
<%= render "posts/form" %>