ActionController::UrlGenerationError in Valuations#new

问题

I've read other SO articles relating to UrlGenerationError's which seem to point to singularization or plurization of a word, but I don't think that's the issue here.

It works when I remove from valuations/_form.html.erb:

<%= render "comments/comments" %>
<%= render "comments/form" %>

Submit the _form with :name & :tag_list, readd

<%= render "comments/comments" %>
<%= render "comments/form" %>

and then refresh. What's the deal when nil?

routes

  resources :valuations do
    resources :comments
  end

comments_controller

class CommentsController < ApplicationController
	before_action :load_commentable
  before_action :set_comment, only: [:show, :edit, :update, :destroy]
  before_action :logged_in_user, only: [:create, :destroy]

	def index
		@comments = @commentable.comments
	end

	def new
		@comment = @commentable.comments.new
	end

	def create
		@comment = @commentable.comments.new(comment_params)
		if @comment.save
			@comment.create_activity :create, owner: current_user 
			redirect_to @commentable, notice: "comment created."
		else
			render :new
		end
	end

	def edit
		@comment = current_user.comments.find(params[:id])
	end

	def update
		@comment = current_user.comments.find(params[:id])
		if @comment.update_attributes(comment_params)
			redirect_to @commentable, notice: "Comment was updated."
		else
			render :edit
		end
	end

	def destroy
		@comment = current_user.comments.find(params[:id])
		@comment.destroy
		@comment.create_activity :destroy, owner: current_user
		redirect_to @commentable, notice: "comment destroyed."
	end

private
  def set_comment
    @comment = Comment.find(params[:id])
  end

	def load_commentable
		resource, id = request.path.split('/')[1, 2]
		@commentable = resource.singularize.classify.constantize.find(id)
	end

	def comment_params
		params.require(:comment).permit(:content, :commentable)
	end
end

valuations_controller

class ValuationsController < ApplicationController
  before_action :set_valuation, only: [:show, :edit, :update, :destroy]
  before_action :logged_in_user, only: [:create, :destroy]

  def index
    if params[:tag]
      @valuations = Valuation.tagged_with(params[:tag])
    else
      @valuations = Valuation.order('RANDOM()')
    end
  end

  def show
    @valuation = Valuation.find(params[:id])
    @commentable = @valuation
    @comments = @commentable.comments
    @comment = Comment.new
  end

  def new
    @valuation = current_user.valuations.build
    @commentable = @valuation
    @comments = @commentable.comments
    @comment = Comment.new
  end

  def edit
  end

  def create
    @valuation = current_user.valuations.build(valuation_params)
    if @valuation.save
      redirect_to @valuation, notice: 'Value was successfully created'
    else
      @feed_items = []
      render 'pages/home'
  end
end

  def update
    if @valuation.update(valuation_params)
      redirect_to @valuation, notice: 'Value was successfully updated'
    else
      render action: 'edit'
  end
end

  def destroy
    @valuation.destroy
    redirect_to valuations_url
  end

private
    def set_valuation
      @valuation = Valuation.find(params[:id])
    end

    def correct_user
      @valuation = current_user.valuations.find_by(id: params[:id])
      redirect_to valuations_path, notice: "Not authorized to edit this valuation" if @valuation.nil?
    end

    def valuation_params
      params.require(:valuation).permit(:name, :private_submit, :tag_list, :content, :commentable, :comment)
    end
end

comments/_form.html.erb

<%= form_for [@commentable, @comment] do |f| %>
  <% if @comment.errors.any? %>
    <div class="error_messages">
      <h2>Please correct the following errors.</h2>
      <ul>
      <% @comment.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

<div class="america">

  <div class="form-group">
    <%= f.text_area :content, rows: 4, class: 'form-control', placeholder: 'Enter Comment' %>
  </div>

  <div class="america2">
  <%= button_tag(type: 'submit', class: "btn") do %>
  <span class="glyphicon glyphicon-plus"></span> Comment
  <% end %>

</div>

<% end %>

Thank you so much for your time.

回答1:

When you have a nested resource like that, the url for creating a comment looks like /valuations/123/comments where 123 is the id of the valuation - without a valuation id this url cannot be generated.

On your Valuations#new page, the valuation (i.e. @commentable) is an unsaved object, so it has no id yet, hence the error about a missing valuation_id. In addition having one form nested within another is invalid html and will lead to odd behaviour. On your show page on the other hand, the valuation does have an id and so things should work as they are.

If you want to create a valuation and its initial comment(s) in one go then you should use accepts_nested_attributes_for and fields_for to add the fields for the comments to your valuation form (There are other ways, but accepts_nested_attributes_for is what is built into rails)

来源：https://stackoverflow.com/questions/29157795/actioncontrollerurlgenerationerror-in-valuationsnew