how can i set value from dropdown list on rails? - ruby-on-rails

Question

i am beginner on rails. I have product - brands list.
routes rb
Rails.application.routes.draw do
get 'welcome/index'
# For details on the DSL available within this file, see https://guides.rubyonrails.org/routing.html
resources :brands do
resources :products
end
root 'welcome#index'
end
Brand.rb
class Brand < ApplicationRecord
has_many :products, dependent: :destroy
validates :title, presence: true,
length: { minimum: 2 }
end
Product.rb
class Product < ApplicationRecord
belongs_to :brand
end
products.controller
class ProductsController < ApplicationController
#before_action :set_brand
skip_before_action :verify_authenticity_token
def new
if params[:brand_id]
#brand = Brand.find(params[:brand_id])
end
#product = Product.new
end
def edit
#brand = #product.brand
#product = Product.find(params[:id])
end
def update
#brand = Brand.find(params[:brand_id])
#product = Product.find(params[:id])
#product.update(product_params)
redirect_to brand_path(#brand)
end
def create
#brand = Brand.find(params[:brand_id])
#product = #brand.products.create(product_params)
redirect_to brand_path(#brand)
end
def destroy
#brand = Brand.find(params[:brand_id])
#product = #brand.products.find(params[:id])
#product.destroy
redirect_to brand_path(#brand)
end
def update
#brand = Brand.find(params[:brand_id])
#product = #brand.products.find(params[:id])
#product.destroy
end
helper_method :update
private
def product_params
params.require(:product).permit(:name)
end
def set_brand
#brand = Brand.find(params[:brand_id])
end
end
.../products/new.html.erb
<h1>Add a new product</h1>
<%= form_with(model: [ #brand, #brand.products.build ], local: true) do |form| %>
<p>
<%= form.label :name,"Product name: " %><br>
<%= form.text_field :name %>
</p>
<p>
</p>
<%= form.label :title,"Select a Brand" %>
<%= form.collection_select(:brand_id, Brand.all, :id, :title,{selected: #brand.id}) %>
<p>
<%= form.submit "Add a product" %>
</p>
<% end %>
new.html.erb picture
so i want to set brand_id from selected item on dropdown list. This case, i select first item for brand_id but i cant change the brand_id. How can i set brand_id which is selected from dropdown list ? and how can i save it.

Answer 1

You forgot to permit the parameter in product_params. Which should be:
params.require(:product).permit(:name, :brand_id)
Unpermitted parameters are ignored by the create and update methods.

Answer 2

Since you already have setup products as a nested resource you neither need or want that select. The brand_id param will be passed through the path (the action attribute of the form). The user would choose what brand he wants to add a product to by what link he clicked to get to the new form.
While you could add a select to the form its a major WTF moment when you send:
POST /brands/1/products, { products: { brand_id: 5 }}
And it ends up creating a product that does not belong to Brand 1. If the param from the form was blank you would also get a really strange result.
If really wanted a form where the user selects the "target" brand on the form itself you would create a non-nested respresentation:
<%= form_with(model: #product) do |f| %>
<%= f.collection_select :brand_id %>
<% end %>
class ProductsController < ApplicationController
# GET /products/new
def new
#product = Product.new
end
# POST /products
def create
#product = Product.new(product_params)
if #product.save
redirect_to #product
else
render :new
end
end
def product_params
params.require(:product).permit(:foo, :bar, :brand_id)
end
end