No method error in controller create action

Question

I have read a number of Q&As on SO in search of some help on this but have so far not solved my issue. I am trying to teach myself ruby/rails, and as a test project, I want to create a list of tvshows and a list of characters where each tvshow has_many characters and each character belongs_to a specific show. I am sure I am doing something basic incorrectly. Any assistance would be greatly appreciated.

here is the characters controller:

    class CharactersController < ApplicationController
  before_action :set_character, only: [:show, :edit, :update, :destroy]

  # GET /characters
  # GET /characters.json
  def index
    @characters = Character.all
  end

  # GET /characters/1
  # GET /characters/1.json
  def show
  end

  # GET /characters/new
  def new
    @character = Character.new
  end

  # GET /characters/1/edit
  def edit
  end

  # POST /characters
  # POST /characters.json
  def create
    @character = @tvshow.characters.create(params[:character])

    respond_to do |format|
      if @character.save
        format.html { redirect_to @character, notice: 'Character was successfully created.' }
        format.json { render action: 'show', status: :created, location: @character }
      else
        format.html { render action: 'new' }
        format.json { render json: @character.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /characters/1
  # PATCH/PUT /characters/1.json
  def update
    respond_to do |format|
      if @character.update(character_params)
        format.html { redirect_to @character, notice: 'Character was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: 'edit' }
        format.json { render json: @character.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /characters/1
  # DELETE /characters/1.json
  def destroy
    @character.destroy
    respond_to do |format|
      format.html { redirect_to characters_url }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_character
      @character = Character.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def character_params
      params.require(:character).permit(:first_name, :last_name, :bio)
    end
end

character model:

class Character < ActiveRecord::Base
belongs_to :tvshow
default_scope -> { order('created_at DESC') }
validates :tvshow_id, presence: true
end

tvshow model:

class Tvshow < ActiveRecord::Base
has_many :characters, dependent: :destroy
end

error gets returned when I attempt to create a character. here is the full trace:

app/controllers/characters_controller.rb:27:in `create'
actionpack (4.0.0) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (4.0.0) lib/abstract_controller/base.rb:189:in `process_action'
actionpack (4.0.0) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (4.0.0) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (4.0.0) lib/active_support/callbacks.rb:413:in     `_run__1211653665462320621__process_action__callbacks'
activesupport (4.0.0) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.0) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (4.0.0) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (4.0.0) lib/action_controller/metal/instrumentation.rb:31:in `block in process_action'
activesupport (4.0.0) lib/active_support/notifications.rb:159:in `block in instrument'
activesupport (4.0.0) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.0.0) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.0.0) lib/action_controller/metal/instrumentation.rb:30:in `process_action'
actionpack (4.0.0) lib/action_controller/metal/params_wrapper.rb:245:in `process_action'
activerecord (4.0.0) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (4.0.0) lib/abstract_controller/base.rb:136:in `process'
actionpack (4.0.0) lib/abstract_controller/rendering.rb:44:in `process'
actionpack (4.0.0) lib/action_controller/metal.rb:195:in `dispatch'
actionpack (4.0.0) lib/action_controller/metal/rack_delegation.rb:13:in `dispatch'
actionpack (4.0.0) lib/action_controller/metal.rb:231:in `block in action'
actionpack (4.0.0) lib/action_dispatch/routing/route_set.rb:80:in `call'
actionpack (4.0.0) lib/action_dispatch/routing/route_set.rb:80:in `dispatch'
actionpack (4.0.0) lib/action_dispatch/routing/route_set.rb:48:in `call'
actionpack (4.0.0) lib/action_dispatch/journey/router.rb:71:in `block in call'
actionpack (4.0.0) lib/action_dispatch/journey/router.rb:59:in `each'
actionpack (4.0.0) lib/action_dispatch/journey/router.rb:59:in `call'
actionpack (4.0.0) lib/action_dispatch/routing/route_set.rb:655:in `call'
rack (1.5.2) lib/rack/etag.rb:23:in `call'
rack (1.5.2) lib/rack/conditionalget.rb:35:in `call'
rack (1.5.2) lib/rack/head.rb:11:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/flash.rb:241:in `call'
rack (1.5.2) lib/rack/session/abstract/id.rb:225:in `context'
rack (1.5.2) lib/rack/session/abstract/id.rb:220:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/cookies.rb:486:in `call'
activerecord (4.0.0) lib/active_record/query_cache.rb:36:in `call'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:626:in `call'
activerecord (4.0.0) lib/active_record/migration.rb:369:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.0.0) lib/active_support/callbacks.rb:373:in     `_run__2792846465963916895__call__callbacks'
activesupport (4.0.0) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/reloader.rb:64:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.0.0) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.0.0) lib/rails/rack/logger.rb:21:in `block in call'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `block in tagged'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:25:in `tagged'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `tagged'
railties (4.0.0) lib/rails/rack/logger.rb:21:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.5.2) lib/rack/methodoverride.rb:21:in `call'
rack (1.5.2) lib/rack/runtime.rb:17:in `call'
activesupport (4.0.0) lib/active_support/cache/strategy/local_cache.rb:83:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/static.rb:64:in `call'
railties (4.0.0) lib/rails/engine.rb:511:in `call'
railties (4.0.0) lib/rails/application.rb:97:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
rack (1.5.2) lib/rack/content_length.rb:14:in `call'
rack (1.5.2) lib/rack/handler/webrick.rb:60:in `service'
/Users/dariusgoore/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
/Users/dariusgoore/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
/Users/dariusgoore/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/server.rb:191:in `block in     start_thread'

Answer 1

You can check out my nested attributes example i.e. on Nested Attributes example

I think the following code will help you.

def new
  @tvshow = Tvshow.find() # requires Tv show id in params so you can pass it in find block
  @character = @tvshow.characters.build
end

def create
  @character = Character.new(character_params)

  respond_to do |format|
    if @character.save
      format.html { redirect_to @character, notice: 'Character was successfully created.' }
      format.json { render action: 'show', status: :created, location: @character }
    else
      format.html { render action: 'new' }
      format.json { render json: @character.errors, status: :unprocessable_entity }
    end
  end
end

Answer 2

My guess is that you're not setting the @tvshow variable in the CharactersController#create action, and it's complaining about an "undefined method characters for nil:nilClass" because of that.

Answer 3

in your create method replace the following line:

@character = @tvshow.characters.create(params[:character])

with

@character = Character.new(character_params)

Answer 4

For some reason I cannot publish a comment so I will include this as an answer.

I made the changes suggested above, adding (params[:id]) as the argument for tvshow.find in the new action in characters controller.

For some reason, params[:id] does not seem to be providing the tvshow_id that I need. I now get the following error message: Couldn't find Tvshow without an ID Extracted source (around line #17):

15 # GET /characters/new 16 def new 17 @tvshow = Tvshow.find(params[:id]) # requires Tv show id in params so you can pass it in find block 18 @character = @tvshow.characters.build 19 end