Pydantic (or Django Ninja) + Timeflake

 So if you want to publish some model to your rest api, and model is declared using Pydantic or Django Ninja (which is using Pydantic under the hood), here is the solution I came with:

from typing import Any, Annotated

from pydantic import GetCoreSchemaHandler, GetJsonSchemaHandler, TypeAdapter

from pydantic.types import AnyType

from pydantic_core import CoreSchema, core_schema

from pydantic.json_schema import JsonSchemaValue

def vld(x: Any) -> Any:

return x

class TimeflakeType:

@classmethod

def __get_pydantic_core_schema__(

cls, source: type[Any], handler: GetCoreSchemaHandler

) -> core_schema.CoreSchema:

serializer = core_schema.plain_serializer_function_ser_schema(cls._serialize, when_used='json')

if cls is source:

return core_schema.no_info_plain_validator_function(

function=vld, serialization=serializer

)

else:

return core_schema.no_info_before_validator_function(

function=vld, schema=handler(source), serialization=serializer

)

@classmethod

def __get_pydantic_json_schema__(cls, cs: CoreSchema, handler: GetJsonSchemaHandler) -> JsonSchemaValue:

return handler(core_schema.str_schema())

@staticmethod

def _serialize(v: Any) -> str:

return str(v)

def __repr__(self) -> str:

return 'Timeflake'

This code is based on ImportString type declaration in standard Pydantic repo.