class TrustyCms::Config

set a value that is not among those permitted.
so this will raise a ConfigError if you try to change a protected config entry or a RecordInvalid if you
Calling value= also applies any validations and restrictions that are found in the associated definition.

TrustyCms::Config.find_or_create_by_key('key').value = value

is equivalent to this:

TrustyCms.config['key'] = value

The usual way to use a config item:

def value=(param)
  newvalue = param.to_s
  if newvalue != self[:value]
    raise ConfigError, "#{self.key} cannot be changed" unless settable? || self[:value].blank?
    if boolean?
      self[:value] = (newvalue == "1" || newvalue == "true") ? "true" : "false"
    else
      self[:value] = newvalue
    end
    self.save!
  end
  self[:value]
end