Rails 4 form_for double nested comments

问题:

First of all, I've found some very helpful answers already (see links below), but I'm still struggling to make this work. I haven't been programming for long, and this is definitely stretching what I feel comfortable claiming to understand.

I have three models. For example's sake, I'll call them Tree, Bark, Engraving (the comments). I'm trying to add a simple form partial for users to submit new comments (engravings).

The below setup is producing the error:

NoMethodError at /trees/1 undefined method `tree' for nil:NilClass

Controllers

class TreesController < ApplicationController
  def show
   @barks = Bark.where(tree_id: @tree.id)
   @engraving= Engraving.new( :bark=> @bark)  
  end
end

class BarksController < ApplicationController
  def show
   @engravin= Engraving.new( :bark=> @bark)
   @engravings = Engraving.where(bark_id: @bark.id)  
  end
end

class EngravingsController < ApplicationController
  def show
   @bark= Bark.find(params[:bark_id])
   @engraving = Engraving.new(params[:engraving])  
  end
end

def create
@bark = Bark.find(params[:bark_id])
@engraving = Engraving.new(params[:engraving])
@engraving.user_id = current_user.id


respond_to do |format|
  if @engraving.save
    format.html { redirect_to tree_bark_path(@tree, @bark), notice: 'Comment was       successfully created.' }
    format.json { render action: 'show', status: :created, location: @engraving}
  else
    format.html { render action: 'new' }
    format.json { render json: @engraving.errors, status: :unprocessable_entity }
  end
end

end

Models

class Tree < ActiveRecord::Base
  belongs_to :user
  has_many :barks
  has_many :engravings, through: :barks
end

class Bark< ActiveRecord::Base
  belongs_to :user
  belongs_to :tree
  has_many :engravings

  delegate :title, :link, :to => :tree, :prefix => true

  def new_engraving_path
    Rails.application.routes.url_helpers.new_tree_bark_engraving_path(book, self)
  end

  def serializable_hash(*args)
    super.merge 'new_engraving_path' => new_engraving_path
  end
end

class Engraving< ActiveRecord::Base
  belongs_to :user
  belongs_to :bark

  delegate :tree, :to => :bark, :prefix => true

  def to_edit_path
    Rails.application.routes.url_helpers.edit_tree_bark_engraving_path bark_tree, bark, self
  end

  def to_path
    Rails.application.routes.url_helpers.tree_bark_engraving_path bark_tree, bark, self
  end

  def serializable_hash(*args)
    super.merge 'path' => to_path, 'edit_path' => to_edit_path
  end
end

Calling the Form in a View

On the Tree show page, I have all the Bark populating there. Clicking on an Bark element opens a modal, where the Bark.content and Engravings are shown. Under the last Engraving, I want to have a text_area form to create a new Engraving, and add it to this "piece" of bark.

# trees\show.html.erb
<%= render @barks %>

# barks\_bark.html.erb
<%= render partial: 'barks/modal', locals: { bark: bark} %>

# barks\modal.html.erb
<% render partial: '/engravings/simpleForm', :collection => bark.engravings %>

# Form partial

  <%= form_for @engraving, :url => (new_tree_bark_engraving_path(:tree_id => @bark.tree, :bark_id => @bark.id)) do |f| %>
    <%= f.hidden_field :bark_id %> 

     <div class="field">
      <%= f.text_area :content %>
     </div>

     <div class="actions">
      <%= f.submit %>
     </div>
  <% end %>

Routes

    get "pages/home"

    resources :trees do
      collection do
        get 'search'
        post 'load_from_api'
      end
    resources :barks do
      resources :engravings
    end
  end
    resources :barks do
      resources :engravings
    end

  root "trees#index"

---

Other Answer Sources

Rails Routing Error for nested form_for

Twice Nested Resource Form_For Issue

form_for with nested resources

回答1:

Your error message NoMethodError at /trees/1 undefined method 'tree' for nil:NilClass means that somewhere you must be calling .tree on a nil object. The only place I can see that happening is in the form partial. I'm assuming that @bark.tree is failing.

From your question it is not clear which controller you are rendering the partial from, but the most likely cause is that @bark is not being passed into the form. Make sure that you are passing @bark into your partial, here is an example:

<%= render partial: "form", locals: {bark: @bark} %>

回答2:

You're definining @barks in your trees#show action, but never @bark

def show @barks = Bark.where(tree_id: @tree.id) @engraving= Engraving.new( :bark=> @bark) end

So @bark is nil.