Polyfactory with association tables

[aranvir]

Hi, I just started to look into polyfactory for mock data generation for my database model. I think I ran into an issue with regards to association tables to model many-to-many relationships (creating batch data for the example model without the relationships works). I attached my code below.

The model idea is simple: There are many projects and many users. Each project has a list of users and each user can work for a list of projects - thus the association table. I took the example from the sqlalchemy docs.

When I run the code I get the following error:

sqlalchemy.exc.ArgumentError: reverse_property 'user' on relationship Project.user_associations references relationship ProjectUser.user, which does not reference mapper Mapper[Project(project)]

I also tried to create factories for Project and User to generate the data this way (with set_relationships disabled) but it's raising the same error.

"""
Minimal example to demonstrate mock data generation with polyfactory for
a model with two tables that are linked via an association table.
"""
from typing import List, Type

import sqlalchemy.exc
from sqlalchemy import BigInteger, ForeignKey, DateTime, text
from sqlalchemy.orm import Session
from sqlalchemy.orm import DeclarativeBase
from sqlalchemy.orm import Mapped, mapped_column, relationship
from polyfactory.factories.sqlalchemy_factory import SQLAlchemyFactory, T

from engine import get_engine


class Base(DeclarativeBase):
    ...


PROJECT_TABLE = "project"
USER_TABLE = "user"
PROJECT_USER_TABLE = "project_user"


class Project(Base):
    __tablename__ = PROJECT_TABLE

    id: Mapped[int] = mapped_column(BigInteger(), primary_key=True)
    name: Mapped[str] = mapped_column(unique=True, nullable=False)

    users: Mapped[List["User"]] = relationship(secondary=PROJECT_USER_TABLE, back_populates="projects", viewonly=True)
    user_associations: Mapped[List["ProjectUser"]] = relationship(back_populates="user")


class User(Base):
    __tablename__ = USER_TABLE

    id: Mapped[int] = mapped_column(BigInteger(), primary_key=True)
    name: Mapped[str] = mapped_column(unique=True, nullable=False)

    projects: Mapped[List[Project]] = relationship(secondary=PROJECT_USER_TABLE, back_populates="users", viewonly=True)
    project_associations: Mapped[List["ProjectUser"]] = relationship(back_populates="project")


class ProjectUser(Base):
    __tablename__ = PROJECT_USER_TABLE

    assignment_id: Mapped[int] = mapped_column(BigInteger(), primary_key=True)
    mission_id: Mapped[int] = mapped_column(ForeignKey(f"{PROJECT_TABLE}.id"), nullable=False)
    user_id: Mapped[int] = mapped_column(ForeignKey(f"{USER_TABLE}.id"), nullable=False)

    project: Mapped[Project] = relationship(back_populates="user_associations")
    user: Mapped[User] = relationship(back_populates="mission_associations")


class BaseFactory(SQLAlchemyFactory[T]):
    __is_base_factory__ = True
    __set_relationships__ = False
    __randomize_collection_length__ = True
    __min_collection_length__ = 3


if __name__ == "__main__":
    engine = get_engine("association_test")
    try:
        with engine.connect() as conn:
            conn.execute(text(f"DROP TABLE IF EXISTS {PROJECT_TABLE},{USER_TABLE},{PROJECT_USER_TABLE} CASCADE;"))
            conn.commit()
    except sqlalchemy.exc.ProgrammingError:
        pass
    Base.metadata.create_all(engine)
    session = Session(engine)

    BaseFactory.__session__ = session

    projects = BaseFactory.create_factory(Project).create_batch_sync(5)
    users = BaseFactory.create_factory(User).create_batch_sync(10)

[adhtruong]

Hi, I've tried the example locally and used process_kwargs and relationships are omitted there for Python 3.12 and head of main.

Are you able to instantiate these models not using a factory? It may be missing a link between these relationships

[aranvir]

Good point, can't instantiate a model on it's own. Gonna investigate that further.

[aranvir]

Silly mix-up on my side: user_associations and project_associations had the wrong back_population set. Having user_associations back populate user and project_associations back populate project instead works!