Good notes posted by bradcantin

uniqueness

You can scope uniqueness as well

validates :user_name, :presence => true, :uniqueness => {:scope => :account_id}

# the old way  
validates_uniqueness_of :user_name, :scope => :account_id

multiple attributes with the same validations

You can list multiple attributes if they share the same validations

validates :title, :body, :presence => true

sending the attributes as an array will return an error

validates [:title, :body], :presence => true
#=> ArgumentError: Attribute names must be symbols