class DateTime

def self.json_create(object)

See #as_json. 
def self.json_create(object)
  args = object.values_at('y', 'm', 'd', 'H', 'M', 'S')
  of_a, of_b = object['of'].split('/')
  if of_b and of_b != '0'
    args << Rational(of_a.to_i, of_b.to_i)
  else
    args << of_a
  end
  args << object['sg']
  civil(*args)
end

def as_json(*)


DateTime.json_create(x) # BUG? Raises Date::Error "invalid date"

\Method +JSON.create+ deserializes such a hash, returning a \DateTime object:

# => {"json_class"=>"DateTime", "y"=>2023, "m"=>11, "d"=>21, "sg"=>2299161.0}
x = DateTime.now.as_json
require 'json/add/datetime'

returning a 2-element hash representing +self+:
\Method DateTime#as_json serializes +self+,

see Marshal[https://docs.ruby-lang.org/en/master/Marshal.html].
to serialize and deserialize a \DateTime object;
Methods DateTime#as_json and +DateTime.json_create+ may be used 
def as_json(*)
  {
    JSON.create_id => self.class.name,
    'y' => year,
    'm' => month,
    'd' => day,
    'H' => hour,
    'M' => min,
    'S' => sec,
    'of' => offset.to_s,
    'sg' => start,
  }
end

def to_json(*args)


{"json_class":"DateTime","y":2023,"m":11,"d":21,"sg":2299161.0}

Output:

puts DateTime.now.to_json
require 'json/add/datetime'

Returns a JSON string representing +self+: 
def to_json(*args)
  as_json.to_json(*args)
end