On Mon, May 6, 2019 at 12:06 AM <jens.troe...@gmail.com> wrote:
>
> Suppose the following code:
>
> # We define a base for all DB objects, currently empty.
> class _Base:
> pass
>
> Base = declarative_base(cls=_Base, metadata=MetaData(naming_convention=…))
>
> # Then the objects.
> class User(Base):
> __tablename__ = "users"
>
> id = Column(UUID(), default=uuid.uuid4, primary_key=True)
> …
>
> For the majority of code this works well and the id is initialized whenever
> the object is committed. However, there are cases when I need to get a hold
> of a new object’s id and that happens before the commit. In such cases the id
> is not set yet, and I have extra code which sets the id manually.
>
> That feels crummy to me.
>
> Now I wonder if that’s poor implementation because a new object should always
> be committed before use, or if I should perhaps expand the _Base class, for
> example:
>
> class _Base:
>
> def __init__(self, *args, **kwargs):
> super().__init__(args, kwargs)
> if hasargs(self, "id"):
> self.id = uuid.uuid4()
>
> That way, every object would have an id assigned and if the object is loaded
> from the db then that initial id would be overwritten. Not pretty either, but
> maybe less crummy than the current implementation.
>
> What are your thoughts?
yes but here is the most canonical approach:
import uuid
from sqlalchemy import Column
from sqlalchemy import event
from sqlalchemy.dialects.postgresql import UUID
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class HasUUID(object):
id = Column(UUID(), default=uuid.uuid4, primary_key=True)
@event.listens_for(HasUUID, "init", propagate=True)
def init(obj, arg, kw):
obj.id = uuid.uuid4()
class User(HasUUID, Base):
__tablename__ = 'user'
u1 = User()
print(u1.id)
Alternatively, you can write an event that scans for columns that
contain a Python level default and invokes them. I think I did this
for someone once but it's apparently not in the wiki, but in any case
doing this using class-level inheritance is IMO the cleanest way since
your User class takes on the role of HasUUID explicitly.
>
> Much thanks!
> Jens
>
> --
> You received this message because you are subscribed to the Google Groups
> "sqlalchemy-alembic" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to sqlalchemy-alembic+unsubscr...@googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy-alembic" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to sqlalchemy-alembic+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
