[RUBY] [Rails] EC site cart function


I created an EC site with Ruby on Rails. At that time, I spent a lot of time implementing the cart function, so I will describe how to do it.


In order to have the cart function, a table is required in the DB. The association with other tables is described in the following article. [Rails] DB design for EC site

The basic part of the cart function

Here we will create a session.

For sessions, the following articles are easy to understand. [Rails] How to use Session

In short, it's a mechanism that retains data. So, I coded the session creation for this cart as follows:

# application_controller.rb
class ApplicationController < ActionController::Base

  #Creating a session
  def current_cart
    #Cart obtained from session_Get Cart information from Cart table based on id
    current_cart = Cart.find_by(id: session[:cart_id])
    #If Cart information does not [email protected]_Create cart
    current_cart = Cart.create unless current_cart
    #Obtain the ID from the obtained Cart information and set it in the session
    session[:cart_id] = current_cart.id
    #Return Cart information

The "current_cart" defined here will be used for other controllers as well.

Add products to the cart

From here, we will use the method created earlier in carts_controller.

class CartsController < ApplicationController
  before_action :set_line_item, only: [:add_item, :destroy]
  before_action :set_user
  before_action :set_cart

  def show
    @line_items = @cart.line_items

  def add_item
    @line_item = @cart.line_items.build(product_id: params[:product_id]) if @line_item.blank?
    @line_item.quantity += params[:quantity].to_i
    if @line_item.save
      redirect_to current_cart
      redirect_to controller: "products", action: "show"

  def destroy
    redirect_to current_cart

  def set_user
    @user = current_user

  def set_line_item
    @line_item = current_cart.line_items.find_by(product_id: params[:product_id])

  def set_cart
    @cart = current_cart

Regarding the add_item action, the "Add to cart" button is installed on the product detail page, and the product is added to the cart using the HTTP method of POST.

@line_item = @cart.line_items.build(product_id: params[:product_id]) if @line_item.blank?

Above, I'm using the build method. build is an alias of new, but it seems that when creating an object of the associated model by convention, build is used and new is used in other cases.

This time, cart is the parent and line_item is the child, so we used build to create an object for the line_item model. (Excuse me if I am wrong)

Basically, I think that it is functioning as a cart so far.

By the way

You can create an EC site in seconds by using a gem called solidus.

Reference article ↓ Installation memo of Solidus, the successor EC system of Spree

I tried using it, but it seems that customization is slow. It may be an ant to try it depending on the purpose.

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