Fix #463 - Fetch and display previews of URLs using OpenGraph tags

db/migrate/20170119214911_create_preview_cards.rb

@@ -0,0 +1,17 @@
+class CreatePreviewCards < ActiveRecord::Migration[5.0]
+  def change
+    create_table :preview_cards do |t|
+      t.integer :status_id
+      t.string :url, null: false, default: ''
+
+      # OpenGraph
+      t.string :title, null: true
+      t.string :description, null: true
+      t.attachment :image
+
+      t.timestamps
+    end
+
+    add_index :preview_cards, :status_id, unique: true
+  end
+end