ActiveRecord::AttributeMethods::Write
Namespace
Methods
W
Instance Public methods
write_attribute(attr_name, value)

Updates the attribute identified by attr_name with the specified value. Empty strings for Integer and Float columns are turned into nil.

Source: show | on GitHub 

# File activerecord/lib/active_record/attribute_methods/write.rb, line 31
def write_attribute(attr_name, value)
  name = if self.class.attribute_alias?(attr_name)
    self.class.attribute_alias(attr_name).to_s
  else
    attr_name.to_s
  end

  name = self.class.primary_key if name == "id".freeze && self.class.primary_key
  @attributes.write_from_user(name, value)
  value
end