SQLAlchemy, OnUpdate & Datetime UTCNOW deprecation in 3.12

This is a quick post about migrating your utcnow() to now(tz=UTC) in SQLAlchemy for your onupdate function argument to your SQL Models.

A World Without utcnow

With datetime.utcnow being deprecated you might see this pattern in your project's code if you are using SQLAlchemy

class Table(Base):
    updated_at: Mapped[timestamp] = mapped_column(
        TIMESTAMP(fsp=3),
        default=datetime.utcnow,
        onupdate=datetime.utcnow,
        nullable=False,
    )

However, you might be wondering how to pass the new recommended datetime.now(tz=UTC) to the function above, as invoking datetime.now() will cause all the timestamps to be the time when the server or lambda started, not when the function for updated is actually called. (It's effectively hard-coding a single time stamp that will never change). The answer is functools.partial where you can pass functions with_arguments to another function as an argument. So the above snippet will become:

from functools import partial

class Table(Base):
    updated_at: Mapped[timestamp] = mapped_column(
        TIMESTAMP(fsp=3),
        default=partial(datetime.now, tz=UTC),
        onupdate=partial(datetime.now, tz=UTC),
        nullable=False
    )

The end.