Mike, I really appreciate your responses, thank you! All makes sense 🤓 Jens
On Tuesday, January 25, 2022 at 4:06:03 PM UTC+10 Mike Bayer wrote: > > > On Mon, Jan 24, 2022, at 11:32 PM, jens.t...@gmail.com wrote: > > Mike, thank you for elaborating, that helps a lot! Yes, I meant a transient > or pending > <https://docs.sqlalchemy.org/en/14/orm/session_state_management.html#quickie-intro-to-object-states> > > object above, you’re correct. > > To make sure I understand correctly: it’s ok to declare > > deleted_at: Mapped[Optional[datetime.datetime]] = > Column(sqlalchemy.DateTime, nullable=True) > > or > > id: Mapped[uuid.UUID] = > Column(sqlalchemy.dialects.postgresql.UUID(as_uuid=True), primary_key=True, > default=uuid.uuid4) > > > where the RHS declares the column’s type by means of a SQLA type and the > LHS’s type a “*mapped”* stdlib Python type? > > > yes, the above syntax is what you can use specifically when the sqlalchemy > mypy plugin is installed, because it will sneak inside the mypy state and > hide those "Column" objects from causing typing errors. > > if you aren't using the plugin, then the above won't work. I'm working > on a new version of declarative that changes the above slightly so that you > can do something basically exactly the same as the above (in a structural > sense, there's a bit of an in-place naming change) without having to use a > mypy plugin. > > > It works here because the column’s type actually is implemented by means > of the LHS stdlib type. I also noticed that I can omit e.g. > Mapped[uuid.UUID] and in some cases mypy is still able to infer the > correct type. > > > In this case, SQLAlchemy's mypy plugin does the inference in this case > based on hardcoded rules that inspect the Column objects. > > > > Much thanks, > Jens > > > On Monday, January 17, 2022 at 1:04:46 AM UTC+10 Mike Bayer wrote: > > > > On Sat, Jan 15, 2022, at 3:34 PM, jens.t...@gmail.com wrote: > > Hello Mike, > > Yes that’s using the plugin: > sqlalchemy[mypy,postgresql_psycopg2binary]==1.4.29 I changed the function > declaration to this: > > @staticmethod > def create(dbsession: Session, name: str, id_: > typing.Union[uuid.UUID, sqlalchemy.dialects.postgresql.base.UUID] = None): > > and it seems to work. In a similar vain, how do I manage the types of > mapped and unmapped objects? Following the above example: > > user = User(dbsession, "Joe Black") > > returns an unmapped, simple User object. Now suppose I have another > existing, mapped User object and would like to assign that newly created > unmapped user: > > other_user.spouse = user > > which creates the following error: > > error: Argument "spouse" to "User" has incompatible type "User"; expected > "Mapped[Any]" [arg-type] > > > if the User class is unmapped, you wouldn't be assigning it to a > relationship attribute like that. > > I think what you might mean is that you have a User object that is what we > call "transient", meaning, it's not yet persisted with any Session. > > again, you would want to set up the relationship attribute with a more > specific annotation: > > class User(...): > # ... > spouse: Mapped[User] = relationship("User", ...) > > > background on this in terms of the plugin is at > https://docs.sqlalchemy.org/en/14/orm/extensions/mypy.html#mapping-relationships > > > > Declaring that column with: > > spouse: typing.Union[Mapped[User], User] = relationship("User", > back_populates="spouse", uselist=False) > seems to work; I just want to make sure that that’s a recommended way of > going about this? Should I always declare a type as a Union between a > mapped and unmapped same class? > > > no that's not correct. The User class is "mapped" at the class level. > you would only need one directive or the other (one of Mapped[User] or > User) when using the Mypy plugin. > > > > > > > > Other than following the migration guide > <https://docs.sqlalchemy.org/en/14/changelog/migration_20.html>, I > haven’t looked into SQLA2 > <https://github.com/sqlalchemy/sqlalchemy/projects/3>. > Jens > > > On Thursday, January 13, 2022 at 11:52:18 PM UTC+10 Mike Bayer wrote: > > > is this with the SQLAlchemy Mypy plugin? current status is for 2.0 we > are looking to move away from the plugin model and pretty much change how > these things work. Otherwise if this is with the plugin, you would use > "id: Mapped[uuid.UUID] = ..." > > > -- > SQLAlchemy - > The Python SQL Toolkit and Object Relational Mapper > > http://www.sqlalchemy.org/ > > To post example code, please provide an MCVE: Minimal, Complete, and > Verifiable Example. 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