Refactor Article and Comment with Visible concern

Refactor out the repeated constant, validation, and instance methods in
the Article and Comment models into a concern module Visible that
extends ActiveSupport::Concern.

Add a new class method called public_count to the Visible module and use
the pluralize helper from ActiveSupport to include the count of public
articles in the Articles index action.

Completes Rails Getting Started Guide:
* 9 Refactoring
  * 9.3 Using Concerns

app/models/article.rb

@@ -1,14 +1,8 @@
 class Article < ApplicationRecord
+  include Visible
+
   has_many :comments, dependent: :destroy
 
   validates :title, presence: true
   validates :body, presence: true, length: { minimum: 10 }
-
-  VALID_STATUSES = %w(public private archived)
-
-  validates :status, inclusion: { in: VALID_STATUSES }
-
-  def archived?
-    status == "archived"
-  end
 end

app/models/comment.rb

@@ -1,11 +1,5 @@
 class Comment < ApplicationRecord
-  belongs_to :article
-
-  VALID_STATUSES = %w(public private archived)
+  include Visible
 
-  validates :status, inclusion: { in: VALID_STATUSES }
-
-  def archived?
-    status == "archived"
-  end
+  belongs_to :article
 end

app/models/concerns/visible.rb

@@ -0,0 +1,19 @@
+module Visible
+  extend ActiveSupport::Concern
+
+  VALID_STATUSES = %w(public private archived)
+
+  included do
+    validates :status, inclusion: { in: VALID_STATUSES }
+  end
+
+  class_methods do
+    def public_count
+      where(status: "public").count
+    end
+  end
+
+  def archived?
+    status == "archived"
+  end
+end

app/views/articles/_form.html.erb

@@ -15,6 +15,11 @@
     <% end %>
   </div>
 
+  <div>
+    <%= form.label :status %><br>
+    <%= form.select :status, %w(public private archived), selected: "public" %>
+  </div>
+
   <div>
     <%= form.submit %>
   </div>

app/views/articles/index.html.erb

@@ -2,6 +2,10 @@
 
 <h1>Articles</h1>
 
+<p class="public-count">
+  Our blog has <%= pluralize(Article.public_count, "article") %> and counting!
+</p>
+
 <ul>
   <% @articles.each do |article| %>
     <% unless article.archived? %>

app/views/comments/_form.html.erb

@@ -7,6 +7,10 @@
     <%= form.label :body %><br>
     <%= form.text_area :body %>
   </p>
+  <p>
+    <%= form.label :status %><br>
+    <%= form.select :status, %w(public private archived), selected: "public" %>
+  </p>
   <p>
     <%= form.submit %>
   </p>

test/controllers/articles_controller_test.rb

@@ -17,6 +17,7 @@ def setup
     assert_select "h1", "Articles"
     assert_select "li", Article.count - 1
     assert_select "a", "New Article"
+    assert_select "p.public-count", "Our blog has 1 article and counting!"
   end
 
   test "should get show" do
@@ -31,15 +32,15 @@ def setup
     assert_select "p.comment-body", @article.comments.count - 1
     assert_select "h2", "Add a comment:"
     assert_select "form"
-    assert_select "form p", 3
+    assert_select "form p", 4
   end
 
   test "should get new" do
     get new_article_url
     assert_response :success
     assert_select "h1", "New Article"
     assert_select "form"
-    assert_select "form div", 3
+    assert_select "form div", 4
   end
 
   test "should create article" do
@@ -76,7 +77,7 @@ def setup
     assert_response :success
     assert_select "h1", "Edit Article"
     assert_select "form"
-    assert_select "form div", 3
+    assert_select "form div", 4
   end
 
   test "should update article" do

test/models/article_test.rb

@@ -87,4 +87,8 @@ def setup
     @article.status = "private"
     assert_not @article.archived?
   end
+
+  test "public count matches number of public records" do
+    assert_equal 1, Article.public_count
+  end
 end

test/models/comment_test.rb

@@ -59,4 +59,8 @@ def setup
     @comment.status = "private"
     assert_not @comment.archived?
   end
+
+  test "public count matches number of public records" do
+    assert_equal 2, Comment.public_count
+  end
 end