Couldn't find Product without an ID build association - ruby-on-rails

Question

I have a problem with Ruby on Rails.When I try to create a line_items which is the association of product and cart ..siguiendo the book Agile web development with Rails.
Here's the code:
def create
product = Product.find(params[:product_id])
##line_item = LineItem.new(line_item_params)
#line_item = #cart.line_items.build(product: product)
respond_to do |format|
if #line_item.save
format.html { redirect_to #line_item.cart,
notice: 'Line item was successfully created.' }
format.json { render action: 'show',
status: :created, location: #line_item }
else
format.html { render action: 'new' }
format.json { render json: #line_item.errors,
status: :unprocessable_entity }
end
end
end
if I uncomment the line:
line_item = LineItem.new(line_item_params)
and comment
#product = Product.find(params[:product_id])
##line_item = #cart.add_product(product: product)
will it work?
I know in the line_item_params method which is the next
def line_item_params
params.require(:line_item).permit(:product_id, :cart_id)
end
allowable parameters defined to create the object.
Can someone help me build this?
Thanks
This is my form Code for the line_items, I can't copy the code because I blocked certain parts of code
<%= form_for(#line_item) do |f| %>
<% if #line_item.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#line_item.errors.count, "error") %> prohibited this line_item from being saved:</h2>
<ul>
<% #line_item.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= f.label :product_id %><br>
<%= f.text_field :product_id %>
</div>
<div class="field">
<%= f.label :cart_id %><br>
<%= f.text_field :cart_id %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
This is the new method
def new
#line_item = LineItem.new
end
This is the Product Model
class Product < ActiveRecord::Base
has_many :line_items
before_destroy :ensure_not_referenced_by_any_line_item
validates :title, :description, :image_url, presence: true
validates :price, numericality: {greater_than_or_equal_to: 0.01}
validates :title, uniqueness: true
validates :image_url, allow_blank: true, format: {
with: %r{\.(gif|jpg|png)\Z}i,
message: 'must be a URL for GIF, JPG or PNG Image.'
}
validates :title, length: {minimum: 10}
#para ultimo producto para cache
def self.latest
Product.order(:updated_at).last
end
private
def ensure_not_referenced_by_any_line_item
if line_items.empty?
return true
else
errors.add(:base, 'Line Items present')
return false
end
end
end
This is the Cart Model
class Cart < ActiveRecord::Base
has_many :line_items, dependent: :destroy
def add_product(product_id)
current_item= line_items.find_by(product_id: product_id)
if current_item
current_item.quantity +=1
else
current_item= line_items.build(product_id: product_id)
end
current_item
end
end
This is the line_item Model
class LineItem < ActiveRecord::Base
belongs_to :product
belongs_to :cart
end
And this is my Module Cart
module CurrentCart
extend ActiveSupport::Concern
private
def set_cart
#cart = Cart.find(session[:cart_id])
rescue ActiveRecord::RecordNotFound
#cart = Cart.create
session[:cart_id] = #cart.id
end
end

Answer 1

Change this and try:
def create
#cart = Cart.find(params[:line_item][:cart_id])
#product = Product.find(params[:line_item][:product_id])
#line_item = #cart.line_items.build(product: #product)
respond_to do |format|
if #line_item.save
format.html { redirect_to #line_item.cart,
notice: 'Line item was successfully created.' }
format.json { render action: 'show',
status: :created, location: #line_item }
else
format.html { render action: 'new' }
format.json { render json: #line_item.errors,
status: :unprocessable_entity }
end
end
end

Answer 2

Thanks a lot Choco , I did what you sent and run
#cart = Cart.find(params[:line_item][:cart_id])
#product = Product.find(params[:line_item][:product_id])
#line_item = #cart.line_items.build(product: #product)
The arrays [:line_item][:cart_id].