Improve db migrations for notification settings

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

db/migrate/20160328112808_create_notification_settings.rb

 class CreateNotificationSettings < ActiveRecord::Migration
   def change
     create_table :notification_settings do |t|
-      t.integer :user_id
-      t.integer :level
-      t.integer :source_id
-      t.string :source_type
+      t.references :user, null: false
+      t.references :source, polymorphic: true, null: false
+      t.integer :level, default: 0, null: false
 
       t.timestamps null: false
     end

db/migrate/20160328115649_migrate_new_notification_setting.rb

@@ -4,7 +4,7 @@
 class MigrateNewNotificationSetting < ActiveRecord::Migration
   def up
     timestamp = Time.now
-    execute "INSERT INTO notification_settings ( user_id, source_id, source_type, level, created_at, updated_at ) SELECT user_id, source_id, source_type, notification_level, '#{timestamp}', '#{timestamp}' FROM members"
+    execute "INSERT INTO notification_settings ( user_id, source_id, source_type, level, created_at, updated_at ) SELECT user_id, source_id, source_type, notification_level, '#{timestamp}', '#{timestamp}' FROM members WHERE user_id IS NOT NULL"
   end
 
   def down

db/schema.rb

@@ -639,10 +639,10 @@ ActiveRecord::Schema.define(version: 20160328121138) do
   add_index "notes", ["updated_at"], name: "index_notes_on_updated_at", using: :btree
 
   create_table "notification_settings", force: :cascade do |t|
-    t.integer  "user_id"
-    t.integer  "level"
-    t.integer  "source_id"
-    t.string   "source_type"
+    t.integer  "user_id",                 null: false
+    t.integer  "source_id",               null: false
+    t.string   "source_type",             null: false
+    t.integer  "level",       default: 0, null: false
     t.datetime "created_at",              null: false
     t.datetime "updated_at",              null: false
   end
@@ -798,9 +798,9 @@ ActiveRecord::Schema.define(version: 20160328121138) do
     t.string   "type"
     t.string   "title"
     t.integer  "project_id"
-    t.datetime "created_at",                               null: false
-    t.datetime "updated_at",                               null: false
-    t.boolean  "active",                                   null: false
+    t.datetime "created_at"
+    t.datetime "updated_at"
+    t.boolean  "active",                default: false,    null: false
     t.text     "properties"
     t.boolean  "template",              default: false
     t.boolean  "push_events",           default: true