Rails 3 to Rails 4 => lambda instead of conditions

r3r4lambda.md

Rails 3

has_many  :active_events, :through => :event_users, 
          :class_name => "Event", 
          :source => :event, 
          :conditions => ['event_users.active = ?',true]

Rails 4

has_many :active_events, through: :event_users,
         class_name: 'Event',
         source: :event,
         -> { where event_users: { active: true } }