Here you're overriding the <code>activities</code> method that was defined by the <code>has_many</code> statement above. If you want the has_many statement to always return them ordered by created_at, you can use a scope:

    has_many :activities, -> { order: 'created_at DESC' }

Some more info: http://guides.rubyonrails.org/association_basics.html#has-many-association-reference