I wanna write a nice TimestampMixin class for my project, I hope it can:

1. created_at: autonow when creation, and never change since that
2. updated_at: autonow when creation
3. updated_at: auto update updated_at if it is not specified when update.

like:

foo = Foo(name='foo') # created_at, updated_at autofilled

time.sleep(3)

foo.name = 'bar' # `updated_at` auto updated!

data_dict = {"name": "bar", "created_at": 1717288789, "updated_at": 1717288801}
foo_from_orm = Foo.model_validate(**data_dict) # `created_at`: 1717288789, `updated_at`: 1717288801 

For now, I have no solution, I can only manually write a on_update function and manually call it everytime when I update the model.

Is there any better solution or any ideas on this issue?

from datetime import datetime, UTC

from pydantic import BaseModel, Field


now_factory = lambda: int(datetime.now(UTC).timestamp())

class TimestampMixin(BaseModel):
    created_at: int = Field(default_factory=now_factory)
    updated_at: int = Field(default_factory=now_factory)

    def on_update(self):
        self.updated_at = now_factory()