Ruby on Rails Association with model - ruby-on-rails

Question

I am beginner Ruby on rails.Application have 4 model.State, Province, District and City.
Model
app/models/state.rb
Class State < ActiveRecord::Base
has_many :provinces
end
app/models/province.rb
Class Province < ActiveRecord::Base
belongs_to :state
has_many :districts
end
app/models/district.rb
Class District < ActiveRecord::Base
belongs_to :province
has_many :cities
end
app/models/city.rb
Class City < ActiveRecord::Base
belongs_to :district
end
Schema.rb
ActiveRecord::Schema.define(version: 20140714165543) do
create_table "states", force: true do |t|
t.string "name"
t.datetime "created_at"
t.datetime "updated_at"
end
create_table "provinces", force: true do |t|
t.string "name"
t.datetime "created_at"
t.datetime "updated_at"
t.integer "state_id"
end
add_index "provinces", ["state_id"], name: "index_provinces_on_state_id"
create_table "districts", force: true do |t|
t.string "name"
t.datetime "created_at"
t.datetime "updated_at"
t.integer "province_id"
end
add_index "districts", ["province_id"], name: "index_districts_on_province_id"
create_table "citys", force: true do |t|
t.string "name"
t.datetime "created_at"
t.datetime "updated_at"
t.integer "district_id"
end
add_index "citys", ["district_id"], name: "index_citys_on_district_id"
end
I am using simple_form gem.I am Create CRUD for all models. My question is
When iam create some state. then i create provinces and assign to state error in browser . state_id is nil
class ProvincesController < ApplicationController
#GET /Provinces/new
def new
#province = Province.new
end
# GET /provinces/1/edit
def edit
end
# POST /provinces
# POST /provinces.json
def create
#province = Province.new(province_params)
respond_to do |format|
if #province.save
format.html { redirect_to #province, notice: 'Province was successfully created.' }
format.json { render :show, status: :created, location: #province }
else
format.html { render :new }
format.json { render json: #province.errors, status: :unprocessable_entity }
end
end
end
end
_form.html.erb in province
<%= simple_form_for(#province) do |f| %>
<% if #province.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#province.errors.count, "error") %> prohibited this province from being saved:</h2>
<ul>
<% #province.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= f.label :name %><br>
<%= f.text_field :name %>
</div>
<%= f.association :state %>
<div class="actions">
<%= f.submit %>
</div>
<% end %>

Answer 1

You are getting state_id is nil because you haven't have it in the list of permitted params.
Change your province_params method to
def province_params
params.require(:province).permit(:name,:state_id)
end
And with the error you are getting
NoMethodError in Province#show
would be most probably due to this line <%= #state.name %> because #state is not defined in your show method.
It should be <%= #province.state.name %> as you are trying to display the state name of the associated province.

Answer 2

Please run the following generator to add the state_id field to the proviences table.
rails g migration add_state_id_to_proviences state_id:integer
then run the migration command
rake db:migrate