last minor fixes

db/migrate/20161002153425_add_join_table_between_users_and_diary_entries.rb

@@ -1,11 +1,19 @@
+require "migrate"
+
 class AddJoinTableBetweenUsersAndDiaryEntries < ActiveRecord::Migration
-  def change
+  def self.up
     create_table :diary_entry_subscriptions, :id => false do |t|
       t.column :user_id, :bigint, :null => false
       t.column :diary_entry_id, :bigint, :null => false
     end
 
-    add_index :diary_entry_subscriptions, [:user_id, :diary_entry_id], :unique => true, :name => "index_diary_subscriptions_on_user_id_and_diary_entry_id"
+    add_primary_key :diary_entry_subscriptions, [:user_id, :diary_entry_id]
     add_index :diary_entry_subscriptions, [:diary_entry_id]
+    add_foreign_key :diary_entry_subscriptions, :diary_entries, :name => "diary_entry_subscriptions_diary_entry_id_fkey"
+    add_foreign_key :diary_entry_subscriptions, :users, :name => "diary_entry_subscriptions_user_id_fkey"
+  end
+
+  def self.down
+    drop_table :diary_entry_subscriptions
   end
 end