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SQLALchemy - Polymorphic association
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| import asyncio | |
| from sqlalchemy import ForeignKey, UniqueConstraint, select | |
| from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine | |
| from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column, relationship, selectin_polymorphic | |
| aengine = create_async_engine("sqlite+aiosqlite:///database2.db") | |
| asession = async_sessionmaker(aengine) | |
| class Base(DeclarativeBase): | |
| pass | |
| class Tenant(Base): | |
| __tablename__ = "tenant" | |
| id: Mapped[int] = mapped_column(primary_key=True) | |
| # Tenant specific | |
| name: Mapped[str] = mapped_column(unique=True) | |
| # Relationships | |
| accounts: Mapped[list["Account"]] = relationship(back_populates="tenant") | |
| class Account(Base): | |
| __tablename__ = "accounts" | |
| # __mapper_args__ = {"polymorphic_identity": "account"} | |
| __table_args__ = (UniqueConstraint("tenant_id", "username"),) | |
| id: Mapped[int] = mapped_column(primary_key=True) | |
| # Account specific | |
| username: Mapped[str] = mapped_column() | |
| # ForeignKeys | |
| profile_id: Mapped[int] = mapped_column(ForeignKey("profile_associations.id")) | |
| tenant_id: Mapped[int] = mapped_column(ForeignKey("tenant.id", ondelete="CASCADE")) | |
| # Relationships | |
| profile = relationship("Profile", lazy="selectin") | |
| tenant = relationship("Tenant", back_populates="accounts", lazy="selectin") | |
| class Profile(Base): | |
| __tablename__ = "profile_associations" | |
| __mapper_args__ = {"polymorphic_on": "profile_type"} | |
| id: Mapped[int] = mapped_column(primary_key=True) | |
| # Discriminator | |
| profile_type: Mapped[str] = mapped_column() | |
| class Staff(Profile): | |
| __tablename__ = "staff" | |
| __mapper_args__ = {"polymorphic_identity": "staff", "polymorphic_load": "selectin"} | |
| # ForeignKeys | |
| id: Mapped[int] = mapped_column(ForeignKey("profile_associations.id"), primary_key=True) | |
| # Staff specific | |
| staff_name: Mapped[str] = mapped_column() | |
| class Teacher(Profile): | |
| __tablename__ = "teachers" | |
| __mapper_args__ = {"polymorphic_identity": "teacher", "polymorphic_load": "selectin"} | |
| # ForeignKeys | |
| id: Mapped[int] = mapped_column(ForeignKey("profile_associations.id"), primary_key=True) | |
| # Teacher specific | |
| teacher_name: Mapped[str] = mapped_column() | |
| class Student(Profile): | |
| __tablename__ = "students" | |
| __mapper_args__ = {"polymorphic_identity": "student", "polymorphic_load": "selectin"} | |
| # ForeignKeys | |
| id: Mapped[int] = mapped_column(ForeignKey("profile_associations.id"), primary_key=True) | |
| # Student specific | |
| student_name: Mapped[str] = mapped_column() | |
| async def create_tables(): | |
| async with aengine.begin() as conn: | |
| await conn.run_sync(Base.metadata.create_all) | |
| async def drop_tables(): | |
| async with aengine.begin() as conn: | |
| await conn.run_sync(Base.metadata.drop_all) | |
| async def main(): | |
| await drop_tables() | |
| await create_tables() | |
| s = asession() | |
| new_tenant = Tenant(name="tenant1") | |
| # New profiles | |
| new_teacher = Teacher(teacher_name="teachername1") | |
| new_staff = Staff(staff_name="staff1") | |
| # New accounts | |
| new_account1 = Account(username="username1") | |
| new_account2 = Account(username="username2") | |
| # Add Accounts to Tenant | |
| new_tenant.accounts.append(new_account1) | |
| new_tenant.accounts.append(new_account2) | |
| # Add Profiles to Accounts | |
| new_account1.profile = new_teacher | |
| new_account2.profile = new_staff | |
| s.add_all([new_tenant, new_account1, new_teacher]) | |
| await s.commit() | |
| print("Teacher account:") | |
| teacher_account = await s.scalar(select(Account).where(Account.username == "username1")) | |
| print(teacher_account.__dict__) | |
| print(teacher_account.profile.teacher_name) | |
| print(teacher_account.profile.profile_type) | |
| print("Staff account:") | |
| staff_account = await s.scalar(select(Account).where(Account.username == "username2")) | |
| print(staff_account.__dict__) | |
| print(staff_account.profile.staff_name) | |
| print(staff_account.profile.profile_type) | |
| await s.close() | |
| if __name__ == "__main__": | |
| asyncio.run(main()) |
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