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Implementing new features with Rails with EDD

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  • avatar
    Name
    Curtis Warcup
    Twitter

Error Driven Development (EDD) is a way to implement new features in a Rails application. We will be implementing a storewide sales feature in our Rails application.

Implementing Storewide Sales

  • admins can create sales
  • marks everything on sale by x% amount.
  • should be able to create sales date ranges

Example: Everything is 20% off from 2022-08-25 to 2022-08-31

Where do you start?

  • use an EDD approach

  • Ability for admins to create sale records

    • name
    • percent_off
    • starts_on (date)
    • ends_on (date)

  • once a sale is active, display it on the products#index page and affect the price of the product

Making a new route

In the config/routes.rb file, we will add a new route:

  namespace :admin do
    root to: 'dashboard#index'
    resources :products, except: %i[edit update show]
    resources :categories, except: %i[edit update show]

		#new
		resources :sales, only: [:index]
	end

use bin/rake routes to see the new route.

Will see a new route:

admin_sales GET    /admin/sales(.:format)          admin/sales#index
  • we have a route, but need a controller and view
    • controller will be admin/sales_controller.rb
    • could use bin/rails g controller admin/sales to generate the controller

Creating the controller

bin/rails g controller <name_name_of_controller>

Use bin/rails g controller admin/sales to generate the controller.

  • creates the controller and the view

We now need an action! We have an empty controller.

Creating the action

  • we need to create an action in the controller
    • we will create an index action
    • this will be the action that will render the view

Recall, actions are methods on the class.

class Admin::SalesController < ApplicationController
	def index
	end
end

Next thing the action needs to do is... - possibly get some data from the database - needs to render a view

class Admin::SalesController < ApplicationController
	def index
		# render :index     # this is implicit
	end
end

But the view index.html.erb does not exist yet!

Creating the view

  • we need to create the view
    • app/views/admin/sales/index.html.erb
<h1>Admin Sales</h1>

Should see this on the page if we visit localhost:3000/admin/sales

Can use a view that is similar to the products#index view.

<section class="admin-products-index">

  <header class="page-header">
    <h1>Admin &raquo; All Sales</h1>
  </header>

  <div class="well">
    <%= link_to '+ New Sale', [:new, :admin, :sale], class: 'btn btn-info' %>
  </div>

  <div class="panel panel-default Sales">

    <table class="table table-bordered">
      <thead>
        <tr>
          <th colspan="2">Name</th>
          <th>Start Date</th>
          <th>End Date</th>
          <th>Status</th>
          <th>Percent Off</th>
          <th></th>
        </tr>
      </thead>
      <tbody>
        <%= render @sales %>  # need to create this instance in our controller
      </tbody>
    </table>

  </div>

</section>
  • will fail on the render @sales line
    • we need to create the @sales instance variable in the controller
  • also fail on the link_to line
    • we need to create the new_admin_sale_path route (does not exist yet)
    • essentially using [:new, :admin, :sale] to generate the path new_admin_sale_path

To make the route new_admin_sale_path work, we need to add a new route to the config/routes.rb file:

	namespace :admin do
		root to: 'dashboard#index'
		resources :products, except: %i[edit update show]
		resources :categories, except: %i[edit update show]
		resources :sales, only: [:index, :new]    # add :new here
	end

This creates the route new_admin_sale_path and the controller action new in the admin/sales_controller.rb file.

admin_sales GET    /admin/sales(.:format)          admin/sales#index
new_admin_sale GET    /admin/sales/new(.:format)      admin/sales#new

now the button should render fine.

Soling the issue with <%= render @sales %>

  • need to create the @sales instance variable in the controller
    • we will use the Sale model to get the data from the database
      • need to create this model first
    • we will use the Sale.all method to get all the sales from the database

Creating the model and migration

bin/rails g model <name_of_model> <attribute_1>:<type> <attribute_2>:<type> ...
  • we need to create the Sale model
    • bin/rails g model Sale name:string percent_off:integer starts_on:date ends_on:date
    • this will create the migration file and the model file
    • we will need to run the migration to create the table in the database
class Admin::SalesController < ApplicationController
	def index
		@sales = Sale.all
	end
end

Running bin/rails g model Sale name:string percent_off:integer starts_on:date ends_on:date will create the migration file and the model file.

class CreateSales < ActiveRecord::Migration[6.1]
	def change
		create_table :sales do |t|
			t.string :name
			t.integer :percent_off
			t.date :starts_on
			t.date :ends_on

			t.timestamps
		end
	end
end

Running the migration

bin/rake db:migrate
  • this will create the table in the database
  • the controller should be able to run Sale.all now

At this point, we do not have any errors. We also need some data in the database for the view to render in the sales table.

Creating some data

You may assume you need a form in order to create a new sale. But we can use the rails console to create some data.

bin/rails c

Sale.create!(name: "X-mas Sale!", percent_off: 20, starts_on: 'Dec 5, 2022', ends_on: 'Dec 25, 2022')
  • uses ActiveRecord to create a new record in the database
  • is taking a hash of attributes
    • takes in one argument (the entire hash)

Creating the _sale.html.erb partial

  • we need to create the _sale.html.erb partial
    • app/views/admin/sales/_sale.html.erb
<tr>
	<td><%= sale.name %></td>
	<td><%= sale.percent_off %></td>
	<td><%= sale.starts_on %></td>
	<td><%= sale.ends_on %></td>
	<td><%= sale.status %></td>
	<td><%= sale.percent_off %></td>
	<td>
		<%= link_to 'Edit', [:edit, :admin, sale], class: 'btn btn-info' %>
		<%= link_to 'Delete', [:admin, sale], method: :delete, data: { confirm: 'Are you sure?' }, class: 'btn btn-danger' %>
	</td>
</tr>
  • sales is a local variable
    • we need to pass in the local variable to the partial
    • we can do this in the render method

How passing partials works render @sales

<%= render @sales %>
  • this is going through the array-like object @sales

Is similar to:

<% @sales.each do |s| %>
	<%= render 'sale', sale: s %>
<% end %>

rendering sale partial for each sale in the array-like object. This would technically work, but we can use the render method to do this for us.

  • if you wanted to do something with the data before rendering the partial, you could do it in the controller
class Admin::SalesController < ApplicationController
	def index
		@sales = Sale.all
		@sales.each do |sale|
			sale.status = 'active'
		end
	end
end

Updating the index view - dynamically rendering a partial

  • we want to show the status of the sale as 'Active', 'Finished', or 'Upcoming'
    • we need to add a method to the Sale model to do this
    • we can use the status method in the partial
<% if sale.ends_on < Date.current %>
	<span> class="label label-danger">Finished</span>
	<% end %>

but we have no way of testing this.

Back in out rails console, we can test this out (bin/rails c)

  • You can use a cool method called 30.days.ago to get a date 30 days ago
Sale.create!(name: "March Sale!", percent_off: 20, starts_on: 30.days.ago, ends_on: 20.days.ago)

Update our view to show the status of the sale

<% if sale.ends_on < Date.current %>
	<span> class="label label-danger">Finished</span>
<% elsif sale.starts_on > Date.current %>
	<span> class="label label-warning">Upcoming</span>
<% end %>

Need a 3rd sale, that is active

Sale.create!(name: "Active Sale!", percent_off: 20, starts_on: 10.days.ago, ends_on: 10.days.from_now)

Update our view to show the status of the sale

<% if sale.ends_on < Date.current %>
	<span> class="label label-danger">Finished</span>
<% elsif sale.starts_on > Date.current %>
	<span> class="label label-warning">Upcoming</span>
<% else %>
	<span> class="label label-success">Active</span>
<% end %>

The issue with this code is it is not very DRY. We are repeating ourselves. We can use a method in the model to do this for us.

Each of these if statement in the view is determining business logic. A view should not be responsible for business logic. We should move this to the model.

We could do something like this:

```erb
<% if sale.finished? %>
	<span> class="label label-danger">Finished</span>
<% elsif sale.starts_on > Date.current %>
	<span> class="label label-warning">Upcoming</span>
<% else %>
	<span> class="label label-success">Active</span>
<% end %>

When we add <% if sale.finished? %>, the view is not doing any business logic, it is just asking the model if the sale is finished. The model is responsible for determining if the sale is finished.

Adding a method to the Sale model (finished?)

class Sale < ApplicationRecord
	def finished?
		ends_on < Date.current
	end

	def upcoming?
		starts_on > Date.current
	end

	def active?
		!finished? && !upcoming?
	end
end
  • we are not explicitly returning true or false
    • Ruby will return the last line of code
    • Ruby will return true if the last line of code is truthy
    • Ruby will return false if the last line of code is falsy

Updating the index view - for the user/client side

  • we have implemented some labels on the admin side to show if an item is on/off sale
  • we need to implement the same labels on the user side

We need to be able to...

  • display if an item is on sale
  • display it on any page
  • update the prices with the sale price

Within the views/layouts/application.html.erb file, we can add a banner above our main yield statement

Recall, this yield

<main class="container">

		# place code here that you want to appear in all your layouts

		<%= yield %>
</main>

<main class="container">

	<% if active_sale? %>
		<p class="alert alert-info">
			There's an active <%= "Back to school" %> sale going on!
			Everything is <%= "20%" %> off!
		</p>
	<% end %>

		<%= yield %>
</main>

When we run this we get an error saying undefined method 'active_sale?' for #<#<Class:0x00007f9b0b0b0e00>:0x00007f9b0b0b0d60>

This is because the active_sale? method is not defined.

We can do this by creating a helper method.

Creating a helper method

  • is found in the app.helpers folder
  • will be a module

Add a method but do not add logic in it yet:

module SalesHelper
	def active_sale?
	end
end

If we run the page we don't get an error. Let's add some logic to this method.

We want to see if there is an active sale:

module SalesHelper
	def active_sale?
		Sale.where("starts_on <= ? AND ends_on => ?", Date.current, Date.current).any?
	end
end

here we are using an SQL query to find any sales that are active

Lets break down this query:

  • we use ? to represent a variable
    • these are passed in as arguments to the method

Basically does this:

Sale.where("starts_on <= Date.current AND ends_on => Date.current")

See more in the Rails Guide

We are still doing a lot of business logic here. We can move this to the model.

Moving the active_sale? method to the Sale model with class methods

  • class methods can be added by using self.
  • add in the logic from the helper method
  • here we are adding an ActiveRecord scope
class Sale < ApplicationRecord

	# Active record scope method
	def self.active
		where("starts_on <= ? AND ends_on => ?", Date.current, Date.current)
	end

	def finished?
		ends_on < Date.current
	end

	def upcoming?
		starts_on > Date.current
	end

	def active?
		!finished? && !upcoming?
	end
end

Could also be done by using a lambda:

class Sale < ApplicationRecord

	# Active record scope method
	scope :active, -> { where("starts_on <= ? AND ends_on => ?", Date.current, Date.current) }

	#...rest of the methods
end

Back in our helper we can now call the active method:

module SalesHelper
	def active_sale?
		Sale.active.any?
	end
end

Much cleaner!

General steps

  • routing
    • config/routes.rb
  • controller
    • bin/rails g controller <name_name_of_controller>
  • action (method inside the controller)
    • def index; end
  • view
    • app/views/<name_name_of_controller>/<name_of_action>.html.erb
  • model (only if we need to access data from the database)
    • bin/rails g model <name_of_model>

Enter rails console

bin/rails c

Similar to irb