module ActiveRecord::Persistence::ClassMethods

def update!(id = :all, attributes)

of +update+, so an exception is raised if the record is invalid and saving will fail.
Updates the object (or multiple objects) just like #update but calls #update! instead 
def update!(id = :all, attributes)
  if id.is_a?(Array)
    if id.any?(ActiveRecord::Base)
      raise ArgumentError,
        "You are passing an array of ActiveRecord::Base instances to `update!`. " \
        "Please pass the ids of the objects by calling `pluck(:id)` or `map(&:id)`."
    end
    id.map { |one_id| find(one_id) }.each_with_index { |object, idx|
      object.update!(attributes[idx])
    }
  elsif id == :all
    all.each { |record| record.update!(attributes) }
  else
    if ActiveRecord::Base === id
      raise ArgumentError,
        "You are passing an instance of ActiveRecord::Base to `update!`. " \
        "Please pass the id of the object by calling `.id`."
    end
    object = find(id)
    object.update!(attributes)
    object
  end
end