/rails-mini-course-sprint2-mod3-student--starter

Primary LanguageRuby

Ruby on Rails - Intermediate Ruby on Rails - Active Record - Project

Setup

Clone the application and bundle install. Then, create, migrate, and seed the database.

Intro

This app is a partially completed API that will power a warehouse fulfillment client application. We have already built the customer and products portions but need to add orders and a way to associate orders with products.

Here is a breakdown of the existing data model for the application:

Customer

attribute type
id integer
email string
created_at datetime
updated_at datetime

Product

attribute type
id integer
name string
cost_cents integer
inventory integer
created_at datetime
updated_at datetime

Order

attribute type
id integer
status string
customer_id integer
created_at datetime
updated_at datetime

OrderProduct

attribute type
id integer
order_id integer
product_id integer
created_at datetime
updated_at datetime

Resources

Here is a breakdown of the existing resource API for the application.

verb resource route controller#action note
GET customer /api/v1/customers api/v1/customers#index list all customers
POST customer /api/v1/customers api/v1/customers#create create a customer
GET customer /api/v1/customers/:id api/v1/customers#show get a customer
PATCH customer /api/v1/customers/:id api/v1/customers#update update a customer
PUT customer /api/v1/customers/:id api/v1/customers#update update a customer
DELETE customer /api/v1/customers/:id api/v1/customers#destroy delete a customer
GET order /api/v1/orders api/v1/orders#index list all orders
GET order /api/v1/customers/:customer_id/orders api/v1/orders#index list all orders for a customer
POST order /api/v1/customers/:customer_id/orders api/v1/orders#create create an order for a customer
GET order /api/v1/orders/:id api/v1/orders#show get a specific order
POST order /api/v1/orders/:id/ship api/v1/orders#ship ship a specific order
GET product /api/v1/products api/v1/products#index list all products
GET product /api/v1/products/:id api/v1/products#show get a specific product
GET product /api/v1/orders/:order_id/products api/v1/products#index list all products for an order
POST product /api/v1/orders/:order_id/products api/v1/products#create add a product to an order

Step One - Add and Utilize ActiveRecord Associations

We can use active record associations to simplify some of our queries and creation logic. We can do this by using assocations in our models that acknowledge the relationships in our data.

  1. Add an association to Customer representing that it can have many associated Orders.
  2. Add associations to OrderProduct representing that it belongs to both an Order and a Product.
  3. Add an association to Product representing that it can have many associated OrderProducts.
  4. Add an association to Product representing that it can have many associated Orders via the relationship with OrderProducts.
    • This is known as a has many through association; OrderProducts acts a join model between Orders and Products.
  5. Add an association to Order to represent that it can have many associated OrderProducts.
  6. Add an association to Order to represent that it can have many associated Products via the relationship with OrderProducts.
  7. Add an association to Order to represent that it belongs to a Customer

Step Two - Utilize ActiveRecord Associations

Notice the instance method products defined on Order. It queries the related OrderProducts and then uses those values to query Products. That is what a has many through does for us automatically. Named associations become instance methods so instead of keeping our own custom products method, delete it and rely on the association instead.

  1. Remove the now unnecessary products instance method on Order.

Similar code is found in the products#index controller action. Instead of doing the full query, find the correct order based on Order id and use the assocation method to get the list of products

  1. Replace OrderProducts query in products#index with simplified association method

products#create can be simplified by using association methods on @order to build an OrderProduct that already includes the order_id

  1. Simplify OrderProduct instantiation by using association build

Step Three - Add ActiveRecord Validations

Customer:

  1. Validate that customer always has an email.

Product:

  1. Validate that a product always has a name.
  2. Validate that a product always has a cost_cents and that it is greater than 0.
  3. Validate that a product always has an inventory and that its greater than or equal to 0

Order:

  1. Validate that an order always has a status and it's value is either "pending" or "shipped"

Step Four - Add Reusable Queries vis Scopes and Use EagerLoading to Improve Problem Queries

We need to convert the available products query into a scope so that it can be reused in several new features we are planning. Currently, it is manually written in the products#index controller action using a where and order clause:

# app/controllers/api/v1/products_controller.rb
@products = Product.where("inventory > ?", 0).order(:cost)
  1. Convert this query to a scope on products named in_stock.
  2. Create another scope that provides the inverse information named out_of_stock that should list all products with 0 inventory ordered by cost.
  3. Use the in_stock scope in the products#index controller action instead of the inline query we have now

Our customers#index controller action does a simple Customer.all query. It then iterates through each query to display the Customer orders as part of the customer resource. This is where the query becomes non performant, it hits the database multiple times (n + 1).

  1. Use eagerloading on the Customer.all call to prevent "n + 1" database queries