SQLAlchemy database adapter might crash on duplicate users under concurrent app instances #1556

sergmi-sh · 2026-01-02T17:08:20Z

sergmi-sh
Jan 2, 2026

The SQLAlchemy database adapter implements:

    async def create(self, create_dict: dict[str, Any]) -> UP:
        user = self.user_table(**create_dict)
        self.session.add(user)
        await self.session.commit()
        await self.session.refresh(user)
        return user

Which is used by the base user manager simply as:

    async def create(
        self,
        user_create: schemas.UC,
        safe: bool = False,
        request: Request | None = None,
    ) -> models.UP:
        """
        ...
        """
        await self.validate_password(user_create.password, user_create)

        existing_user = await self.user_db.get_by_email(user_create.email)
        if existing_user is not None:
            raise exceptions.UserAlreadyExists()

        user_dict = (
            user_create.create_update_dict()
            if safe
            else user_create.create_update_dict_superuser()
        )
        password = user_dict.pop("password")
        user_dict["hashed_password"] = self.password_helper.hash(password)

        created_user = await self.user_db.create(user_dict)

        await self.on_after_register(created_user, request)

        return created_user

No expectations of an IntegrityError, and the code is asking the database for permission instead of forgiveness. I think under concurrent usage of the database in multiple app instances, this will prevent proper error reporting. This shouldn't be anything significant (what are the odds you'd be registering the same email and get requests on multiple services and expect a decent error message), but good SQL patterns are important even when the odds of breakage are low.

I'm putting this into a discussion in case I missed something about how this is actually well-handled. If I didn't miss anything, I think it makes sense to turn into an issue.

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SQLAlchemy database adapter might crash on duplicate users under concurrent app instances #1556

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SQLAlchemy database adapter might crash on duplicate users under concurrent app instances #1556

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sergmi-sh Jan 2, 2026

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sergmi-sh
Jan 2, 2026