Creating the Customers Controller

app/controllers/customers_controller.rb

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+class CustomersController < ApplicationController
+  def index
+    @customers = Customer.all
+  end
+
+  def alphabetized
+    @customers = Customer.order(:full_name)
+  end
+
+  def missing_email
+    @customers = Customer.where(email_address: [nil, ""])
+  end
+end

app/helpers/customers_helper.rb

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+module CustomersHelper
+end

app/views/customers/_customer.html.erb

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+<div class="card mb-4">
+  <div class="card-content">
+    <div class="media">
+      <div class="media-left">
+        <figure class="image is-96x96">
+          <% if customer.image.attached? %>
+            <%= image_tag customer.image, class: "is-rounded" %>
+          <% else %>
+            <%= image_tag "default_profile.png", class: "is-rounded" %>
+          <% end %>
+        </figure>
+      </div>
+      <div class="media-content">
+        <p class="title is-4"><%= customer.full_name %></p>
+        <p class="subtitle is-6">
+          <% if customer.email_address.present? %>
+            <%= customer.email_address %>
+          <% else %>
+            <span class="has-text-danger">No email provided</span>
+          <% end %>
+        </p>
+      </div>
+    </div>
+    <div class="content">
+      <p><strong>Phone:</strong> <%= customer.phone_number %></p>
+      <p><%= customer.notes %></p>
+    </div>
+  </div>
+</div>

app/views/customers/alphabetized.html.erb

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+<h1>Customers#alphabetized</h1>
+<p>Find me in app/views/customers/alphabetized.html.erb</p>

app/views/customers/index.html.erb

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+<h1>Customers#index</h1>
+<p>Find me in app/views/customers/index.html.erb</p>

app/views/customers/missing_email.html.erb

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+<h1>Customers#missing_email</h1>
+<p>Find me in app/views/customers/missing_email.html.erb</p>

config/routes.rb

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 Rails.application.routes.draw do
+  get "customers/index"
+  get "customers/alphabetized"
+  get "customers/missing_email"
   devise_for :admin_users, ActiveAdmin::Devise.config
   ActiveAdmin.routes(self)
   # Define your application routes per the DSL in https://guides.rubyonrails.org/routing.html

test/controllers/customers_controller_test.rb

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+require "test_helper"
+
+class CustomersControllerTest < ActionDispatch::IntegrationTest
+  test "should get index" do
+    get customers_index_url
+    assert_response :success
+  end
+
+  test "should get alphabetized" do
+    get customers_alphabetized_url
+    assert_response :success
+  end
+
+  test "should get missing_email" do
+    get customers_missing_email_url
+    assert_response :success
+  end
+end