#7 Add thumbnail to post, system will auto parse the thumbnail

app/models/post.rb

@@ -5,5 +5,7 @@ class Post < ActiveRecord::Base
   has_many :favorites, as: :favoritable
   has_many :share_instances, as: :sharable
 
+  has_one :thumbnail
+
   validates_presence_of :url, :type
 end

app/models/thumbnail.rb

@@ -3,4 +3,6 @@ class Thumbnail < ActiveRecord::Base
   has_attached_file :file, :path => ":class/:attachment/:id/:basename.:extension"
   validates :file, :attachment_presence => true
   validates_attachment_content_type :file, :content_type => /\Aimage\/.*\Z/
+
+  belongs_to :post
 end

app/serializers/post_serializer.rb

@@ -1,5 +1,9 @@
 class PostSerializer < ActiveModel::Serializer
 
-  attributes :viewed_times, :url, :title, :type, :processed, :good_format, :created_at, :likes_count, :comments_count, :summary
+  attributes :viewed_times, :url, :title, :type, :processed, :good_format, :created_at, :likes_count, :comments_count,
+             :summary, :thumbnail
 
+  def thumbnail
+    object.thumbnail.try(:file).try(:url)
+  end
 end

app/workers/process_post_worker.rb

@@ -9,6 +9,9 @@ class ProcessPostWorker
     post.title = page.title
     post.summary = page.description
     post.processed = true
+    if page.images.best.present?
+      post.create_thumbnail file: URI.parse(page.images.best)
+    end
     post.save
   end
 

db/migrate/20150914122528_add_post_id_to_thumbnail.rb

@@ -0,0 +1,5 @@
+class AddPostIdToThumbnail < ActiveRecord::Migration
+  def change
+    add_column :thumbnails, :post_id, :integer
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20150914121114) do
+ActiveRecord::Schema.define(version: 20150914122528) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -141,6 +141,7 @@ ActiveRecord::Schema.define(version: 20150914121114) do
     t.integer  "file_file_size"
     t.datetime "file_updated_at"
     t.text     "file_meta"
+    t.integer  "post_id"
   end
 
   create_table "users", force: :cascade do |t|