Why isn't SQLAlchemy default column value available before object is committed?

Question

Recently I figured out that SQLAlchemy\'s Column default doesn\'t work as I expect it to:

>>> Base = declarative_base()
>>> class TestModel         


        

Answer 1

You can use the init event to fill defaults. This event listener will do it:

from sqlalchemy import event
from sqlalchemy.orm import mapper
from sqlalchemy.inspection import inspect


def instant_defaults_listener(target, args, kwargs):
    for key, column in inspect(target.__class__).columns.items():
        if column.default is not None:
            if callable(column.default.arg):
                setattr(target, key, column.default.arg(target))
            else:
                setattr(target, key, column.default.arg)


event.listen(mapper, 'init', instant_defaults_listener)