Question

This error has been troubling me for weeks. When I try to build an Item from a specified User and List, the Item is created, but the association, Wish is not.

If i try to do @item.lists.first.name it returns an error:

undefined method 'name' for nil:NilClass

I’m very new to rails, so I’m sure there is something that I have missed or misunderstood. Any help is thus much appreciated!

I have four models:

class User < ActiveRecord::Base
  has_many :lists, dependent: :destroy
  has_many :wishes, through: :lists
  has_many :items, through: :wishes

class List < ActiveRecord::Base
  belongs_to :user
  has_many :wishes, dependent: :destroy
  has_many :items, through: :wishes

class Wish < ActiveRecord::Base
  belongs_to :list
  belongs_to :item

class Item < ActiveRecord::Base
  has_many :wishes
  has_many :lists, through: :wishes

I want to create a new Item from lists_controller.rb show action:

class ListsController < ApplicationController
  def show
    @user = User.find(params[:user_id])
    @list = @user.lists.find(params[:id])
    @item = @list.items.build if current_user?(@user)
    @items = @list.items
  end

class ItemsController < ApplicationController
    def create
        @list = current_user.lists.find(params[:list_id])
        @item = @list.items.build(params[:item])
    if @item.save
      flash[:success] = "Item created!"
      redirect_to @item
    else
      render 'new'
    end
end

My route file looks like this:

Wishlist::Application.routes.draw do
  resources :users do
    resources :lists, only: [:show, :create, :destroy]
  end
  resources :items, only: [:show, :new, :create, :destroy]

The form lists/show.html.erb:

   <div class="modal-body">
     <%= form_for(@item, html: { multipart: true }) do |f| %>
  <div class="field">
        <%= render 'items/fields', f: f %>
         <%= hidden_field_tag :list_id, @list.id %>
  </div>
   </div>

and items/fields:

<%= render 'shared/error_messages', object: f.object %>

<%= f.label :image %>
<%= f.file_field :image %>

<%= f.label :remote_image_url, "or image URL" %>
<%= f.text_field :remote_image_url %>

<%= f.label :title %>
<%= f.text_field :title %>

<%= f.label :link %>
<%= f.text_field :link %>

Update

From the log:

Processing by ItemsController#create as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"pcDVdaDzZz4M17Kwjx8mKw6tTF9MjUvx1woTzaKRWJY=", "item"=>{"image"=>#<ActionDispatch::Http::UploadedFile:0x007fecdd1fd890 @original_filename="profile.jpg", @content_type="image/jpeg", @headers="Content-Disposition: form-data; name=\"item[image]\"; filename=\"profile.jpg\"\r\nContent-Type: image/jpeg\r\n", @tempfile=#<File:/var/folders/6y/j8zfcgmd02x5s439c0np8fjh0000gn/T/RackMultipart20130216-8413-3vzjuj>>, "remote_image_url"=>"", "title"=>"YES", "link"=>"SDFs"}, "list_id"=>"1", "commit"=>"Add"}
  User Load (0.3ms)  SELECT "users".* FROM "users" WHERE "users"."remember_token" = '5AXS8-7-YRyLyGDKYHIZRg' LIMIT 1
  List Load (0.2ms)  SELECT "lists".* FROM "lists" WHERE "lists"."user_id" = 1 AND "lists"."id" = ? LIMIT 1  [["id", "1"]]
   (0.1ms)  begin transaction
  SQL (0.7ms)  INSERT INTO "items" ("created_at", "image", "link", "title", "updated_at") VALUES (?, ?, ?, ?, ?)  [["created_at", Sat, 16 Feb 2013 20:57:10 UTC +00:00], ["image", "profile.jpg"], ["link", "SDFs"], ["title", "YES"], ["updated_at", Sat, 16 Feb 2013 20:57:10 UTC +00:00]]
   (2.7ms)  commit transaction
Redirected to http://localhost:3000/items/1
Completed 302 Found in 830ms (ActiveRecord: 4.0ms)

Answer 1

After lots of googling, and trial and error, I found that I had to build the Wish explicitly. The create action ended up looking like this:

def create
    @list = current_user.lists.find(params[:list_id])
    @item = Item.create!(params[:item])
    @item.wishes.build(list_id: @list.id)
    if @item.save
      flash[:success] = "Item created!"
      redirect_to @item
    else
      render 'new'
    end
end