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

one would prefer default over server default for one of four reasons:

1. you’d like to run a Python function, not a SQL function, for the default (or a SQL expression that needs some per-INSERT Python state also).

2. the default is part of a primary key column. the ORM can’t load a row back without the primary key, so server_default is generally not useful for a PK column when using the ORM.

3. the SQL expression you want to run isn’t supported by the database as a “server default”.

4. You’re dealing with a schema you can’t/don’t want to change.

In this case, when you’d like “foo” to be “0” in your application independent of database operations, the choices are:

1. use __init__(). It’s python!

2. use events.

Here’s __init__():

class TestModel(Base):
   # ...

   def __init__(self):
       self.foo = 0

Here’s events (specifically the init event):

from sqlalchemy import event

@event.listens_for(Foo, "init")
def init(target, args, kwargs):
    target.foo = 0