[BUG] sqlalchemy relationship fields are absent in router response

There is still an issue with sqlalchemy Data Models similar to the https://github.com/tiangolo/fastapi/issues/4

If one has such models relationship as:

Base = declarative_base()

class Parent(Base):
    children = relationship("Child", back_populates="parent")

class Child(Base):
    parent_id = Column(
        Integer,
        ForeignKey('parent.id', onupdate='CASCADE', ondelete='CASCADE'),
        index=True
    )
    parent = relationship("Parent", back_populates="children")

then the JSON response body of the API call does return only parent_id correct value and parent field has undefined value.

However when one uses a helper method like:

def json(self):
       return {
           'parent_id': self.parent_id,
           'parent': self.parent
       }

then response bode has all proper values.

UPDATE:

the same issue occurs with all SqlAlchemy hybrid_property fields.

[tiangolo]

The latest Pydantic version includes “ORM mode”, to solve these specific use cases.

I just finished a deep integration of it into FastAPI, just released it in version 0.30.0 🎉

Here are the new docs: https://fastapi.tiangolo.com/tutorial/sql-databases/

It should solve lazy-loading, hybrid-properties, dynamic attributes, relationships, and others. And it should work with all the ORMs, SQLAlchemy, Peewee, Tortoise ORM, GINO, etc.

You declare the data you want to export in Pydantic models and they take care of extracting it from your ORM models.

[pourquoi]

same issue while waiting for the PR, i’m setting the relationship to load every time:

parent = relationship(“Parent”, back_populates=“children”, lazy=False)