Fetch data from 3 different tables with SQLAlchemy or SQLModel - api

Question

I want to fetch data from 3 tables with SQLAlchemy or SQLModel. For example lets say that my tables are the following:
class A(SQLModel, table=true):
id: int
title: str
class B(SQLModel, table=true):
id: int
a_id: foreign_key("a.id")
name: str
class C(SQLModel, table=true):
id: int
b_id: foreign_key("b.id")
text: str
The response that I want to have is the following:
[
{
"id": 1,
"title": "This is A table",
"b": [
{
"id": 1,
"name": "This is B table",
"c":[
{
"id":1,
"text": "My text from c"
}
]
}
]
}
]
I am trying with selectinload but doesn't work
query = (
select(A)
.where(A.id == a_id)
.options(
selectinload(A.b).joinedload(
B.c
)
)
)
try:
response = (await session.exec(query)).one()
except NoResultFound:
raise HTTPException(status_code=404, detail="Data not found")
Thank you in advance

Answer 1

I have tried these models with newer version of sqlalchemy (not sqlmodel) it works as shown in this example (sqlalchemy=1.4.39)
class A(Base):
__tablename__ = 'a'
id = Column(Integer, primary_key=True)
title = Column(String(length=100))
b = relationship("B", backref="a")
class B(Base):
__tablename__ = 'b'
id = Column(Integer, primary_key=True)
name = Column(String(length=100))
a_id = Column(ForeignKey('a.id', ondelete='CASCADE'))
c = relationship("C", backref="b")
class C(Base):
__tablename__ = 'c'
id = Column(Integer, primary_key=True)
text = Column(String(length=100))
b_id = Column(ForeignKey('b.id', ondelete='CASCADE'))
Query:
stmt = select(A).options(selectinload(A.b).selectinload(B.c))
resp = await session.execute(query)
return resp.scalars().all()
(Prepare pydantic model related to this query)
schema.py
class CResp(BaseModel):
id: int
text: str
class BResp(BaseModel):
id: int
name: str
c: List[CResp]
class AResp(BaseModel):
id: int
title: str
b: List[BResp]
views.py
#app.get("/", response_model=List[AResp])
async def index(session=Depends(get_session)):
query = select(A).options(selectinload(A.b).selectinload(B.c))
resp = await session.execute(query)
return resp.scalars().all()
If you want to use this query with sqlmodel, you can try some other versions of sqlalchemy as mentioned here (SQLModel error: "AttributeError: 'Team' object has no attribute 'heroes'"), sqlmodel has some problems with SQLalchemy 1.4.36+ versions