Add Custom Fields on Topics

db/migrate/20140425135354_add_topic_custom_fields.rb

@@ -0,0 +1,21 @@
+class AddTopicCustomFields < ActiveRecord::Migration
+  def change
+    create_table :topic_custom_fields do |t|
+      t.integer :topic_id, null: false
+      t.string :name, limit: 256, null: false
+      t.text :value
+      t.timestamps
+    end
+
+    add_index :topic_custom_fields, [:topic_id, :name]
+
+    # migrate meta_data into custom fields
+    execute <<-SQL
+      INSERT INTO topic_custom_fields(topic_id, name, value)
+        SELECT id, (each(meta_data)).key, (each(meta_data)).value
+            FROM topics WHERE meta_data <> ''
+    SQL
+
+    remove_column :topics, :meta_data
+  end
+end