HABTM Association Build - ruby-on-rails

Question

I need propagate this values in :departaments_products table: , but I received the error:
I'm using Rails 4
NoMethodError in Products#new
undefined method `departament_id' for #<Product:0x007f916d35d648>
view.html.erb:
<%= form_for(#product) do |f| %>
<% if #product.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#product.errors.count, "error") %> prohibited this product from being saved:</h2>
<ul>
<% #product.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>
<div class="field">
<%= f.label :price %><br>
<%= f.text_field :price %>
</div>
<%= f.collection_select(:departament_id, Departament.all, :id, :name, {:include_blank => true}) %>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
Products_controller:
class ProductsController < ApplicationController
before_action :set_product, only: [:show, :edit, :update, :destroy]
# GET /products
# GET /products.json
def index
#products = Product.all
end
# GET /products/1
# GET /products/1.json
def show
#product = Product.find( params[:id] )
end
# GET /products/new
def new
#product = Product.new
end
# GET /products/1/edit
def edit
end
# POST /products
# POST /products.json
def create
#product = Product.new(product_params)
respond_to do |format|
if #product.save
format.html { redirect_to #product, notice: 'Produto criado com sucesso' }
format.json { render :show, status: :created, location: #product }
else
format.html { render :new }
format.json { render json: #product.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /products/1
# PATCH/PUT /products/1.json
def update
respond_to do |format|
if #product.update(product_params)
format.html { redirect_to #product, notice: 'Product was successfully updated.' }
format.json { render :show, status: :ok, location: #product }
else
format.html { render :edit }
format.json { render json: #product.errors, status: :unprocessable_entity }
end
end
end
# DELETE /products/1
# DELETE /products/1.json
def destroy
#product.destroy
respond_to do |format|
format.html { redirect_to products_url, notice: 'Product was successfully destroyed.' }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_product
#product = Product.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def product_params
params.require(:product).permit(:name, :price)
end
end
Models:
class Departament < ActiveRecord::Base
has_and_belongs_to_many :products
end
class Product < ActiveRecord::Base
has_and_belongs_to_many :departaments
end
Migration:
class AddProductsAndDepartaments < ActiveRecord::Migration
def change
create_table :departaments_products do |t|
t.references :product, :departament
end
end
end

Answer 1

As its a HABTM association, logically you should be selecting multiple departament_ids for a single product. That said, you should include multiple: true option in the collection_select for departament_ids (Notice departament_ids in plural) in your view code:
<%= f.collection_select(:departament_ids, Departament.all, :id, :name, {include_blank: true}, {multiple: true}) %>
Currently, you are accessing it as departament_id (Notice singular) BUT as per HABTM association you get a method named departament_ids (Notice plural) and NOT departament_id which is why you receive error as NoMethodError in Products#new undefined method 'departament_id'
Once you are done with this change, you need to permit the departament_ids field in ProductsController as below:
def product_params
params.require(:product).permit(:name, :price, :departament_ids => [])
end
:departament_ids => [] is used because multiple selection is allowed for departament_ids and so you would receive it as an Array in params hash upon form submission.

Answer 2

Try departament_ids
For has_many => departament_ids
For has_one => departament_id