Question

So based on Ryan Bates rails cast (http://railscasts.com/episodes/196-nested-model-form-revised) I am creating a nested form. The part of the rails application that I am trying to get to work ideally does the following:

• Let a current user ask a question
• Then provide an answer for that question afterwards

I managed to get everything working, except that when I try to submit the form once everything is filled out, I keep getting the following error:

undefined method `meter_id' for nil:NilClass

app/models/answer.rb:13:in `associate_with_meter_id'
app/controllers/questions_controller.rb:13:in `create'

I believe I know what is wrong, but I am not sure how to fix it. The meter_id is returning an undefined value, because it is not being passed the correct value. Here is the method that associates the meter_id (of answers) with the meter_id (of users):

def associate_with_meter_id
    self.meter_id = user.meter_id
end

Here is a partial of my user model

class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :token_authenticatable, :encryptable, :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable

  # Setup accessible (or protected) attributes for your model
  attr_accessible :email, :password, :password_confirmation, :remember_me,
                  :home_size_sf, :meter_id, :avg_monthly_kwh, :discovery_score,
                  :questions_attributes, :answers_attributes


  has_many :data_records, :foreign_key => :meter_id, :primary_key => :meter_id, :class_name => "DataRecord"

  has_many :questions
  has_many :answers

  accepts_nested_attributes_for :questions, :answers

Here is the questions model

class Question < ActiveRecord::Base
    attr_accessible :description, :taxonomy, :user_id, :answers_attributes
  belongs_to :user
  has_many :answers
  accepts_nested_attributes_for :answers
  validates :description, presence: { :on => :create }
  validates :taxonomy, presence: { :on => :create }
  def relevance_score
    rand
  end
end

Here is the questions controller

class QuestionsController < ApplicationController
  respond_to :html, :json

  def index
    @question = current_user.questions.new
    @questions = current_user.questions.all
  end

  def create
    @question = current_user.questions.new(params[:question])
    if !params[:update_button]
      if @question.valid?
        if params[:next_button] || !@question.save
          render 'index'
        elsif !params[:next_button] && params[:submit_button] && @question.save
          flash[:success] = "Your question and answer have been saved."
          respond_with @question, :location => questions_path
        end
      else
        render 'index'
      end
    else
      render 'index'
    end
  end

  def next
    @question = current_user.unanswered.first
    @answer = Answer.new(:question => @question, :user => current_user)
    respond_to do |format|
      format.js
    end
  end
end

answers model

class Answer < ActiveRecord::Base
  attr_accessible :value, :user_id, :meter_id, :question_id
  belongs_to :user
  belongs_to :question

  validates :value, presence: true, :numericality => true

  before_save :associate_with_meter_id



  def associate_with_meter_id
    self.meter_id = user.meter_id **(<-- line 13 from the error message)**
  end

end

answers controller

class AnswersController < ApplicationController
  respond_to :html, :json

  def index
    @answers = current_user.answers
  end

  def create
    @answer = current_user.answers.create(params[:answer])
    if @answer.save
      flash[:notice] = "Thanks for for answer. Please continue with your input...."
      respond_with @answer, :location => root_url
    end
  end

end

database schema

ActiveRecord::Schema.define(:version => 20120210184340) do

  create_table "answers", :force => true do |t|
    t.integer  "meter_id"
    t.integer  "user_id"
    t.integer  "question_id"
    t.float    "value"
    t.float    "what_if_value"
    t.datetime "created_at",    :null => false
    t.datetime "updated_at",    :null => false
  end

  create_table "data_records", :force => true do |t|
    t.datetime "timestamp"
    t.float    "value"
    t.integer  "meter_id"
    t.string   "status_code"
  end

  create_table "questions", :force => true do |t|
    t.string   "description"
    t.string   "taxonomy"
    t.string   "coeff"
    t.float    "rsquare",     :default => 0.0
    t.string   "rank"
    t.string   "responses"
    t.string   "skips"
    t.string   "avganswer"
    t.float    "pval",        :default => 0.0
    t.float    "quality",     :default => 0.0
    t.integer  "user_id"
    t.datetime "created_at",                   :null => false
    t.datetime "updated_at",                   :null => false
  end

  create_table "setup_constants", :force => true do |t|
    t.float "exp_model",      :default => 0.0
    t.float "exp_pval_const", :default => 0.0
  end

  create_table "users", :force => true do |t|
    t.integer  "meter_id"
    t.float    "home_size_sf",           :default => 1000.0
    t.text     "notifications"
    t.float    "avg_monthly_kwh"
    t.float    "ee_score"
    t.string   "email",                  :default => "",     :null => false
    t.string   "encrypted_password",     :default => "",     :null => false
    t.string   "reset_password_token"
    t.datetime "reset_password_sent_at"
    t.datetime "remember_created_at"
    t.integer  "sign_in_count",          :default => 0
    t.datetime "current_sign_in_at"
    t.datetime "last_sign_in_at"
    t.string   "current_sign_in_ip"
    t.string   "last_sign_in_ip"
    t.datetime "created_at",                                 :null => false
    t.datetime "updated_at",                                 :null => false
  end

  add_index "users", ["email"], :name => "index_users_on_email", :unique => true
  add_index "users", ["reset_password_token"], :name => "index_users_on_reset_password_token", :unique => true

end

Note:

In the answers model (above), the line:

self.meter_id = user.meter_id

Associates the meter_id of the answer model with the meter_id of the user model. I believe this is where the issue is. I tried changing the above line to:

self.meter_id = 2

And then everything worked fine, so it’s obvious that the user.meter_id is undefined, so I’m not sure how to pass that value through the nested form? I tried using a hidden field but with no luck (the following is a nested fields_for :answers, within a form_for @questions):

<fieldset>
    <%= f.label "Yes" %>
  <%= f.radio_button :value, 1 %>
  <%= f.label "No" %>
  <%= f.radio_button :value, 0 %>
  <%= f.hidden_field :user_id %>
  <%= f.hidden_field :question_id %>
  <%= f.hidden_field :meter_id %>
</fieldset>

Answer 1

First of all, you don’t want to pass the current user in the view for security reasons. Instead, you want to do it from the controller.

A starting point (assuming you have current_user):

@answer = current_user.answers.create(params[:answer].merge(:user => current_user))

From there, it’s up to you how to pass the user to the answer model. You could, however, use this:

self.meter_id = question.user.meter_id

Assuming that’s appropriate.