Conditionally Loading Related Entities in SQLModel with FastAPI Based on URL Parameter

[samidarko]

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Example Code

@app.get("/teams/{team_id}", response_model=TeamReadWithHeroes)
def read_team(*, team_id: int, include_heroes: bool = False, session: Session = Depends(get_session)):
    team = session.get(Team, team_id)
    if not team:
        raise HTTPException(status_code=404, detail="Team not found")
    return team

Description

I've recently begun working with SQLModel in conjunction with FastAPI and have encountered a challenge regarding conditional loading of related entities. Following the official documentation on Models with Relationships, it appears that the TeamReadWithHeroes model automatically includes the "heroes" relationship. However, I am looking to make the inclusion of "heroes" optional, based on a URL parameter (e.g., "include_heroes=true").

My initial thought was to leverage Pydantic's model_validate along with some context or a discriminator to achieve this. The ideal solution would allow for disabling lazy loading on the relationship unless explicitly joined, providing a default return if the relationship is not included.

Does anyone have a simpler approach or solution to selectively load related entities based on a URL parameter with SQLModel and FastAPI?

Related link:

• https://stackoverflow.com/questions/77936211/conditionally-loading-related-entities-in-sqlmodel-with-fastapi-based-on-url-par
• https://sqlmodel.tiangolo.com/tutorial/fastapi/relationships/#update-the-path-operations

Operating System

Linux

Operating System Details

No response

SQLModel Version

0.0.14

Python Version

3.10

Additional Context

No response

[samidarko]

For now, I opted for the following solution:

TeamResponse = Union[TeamRead, TeamReadWithHeroes]

@app.get("/teams/{team_id}", response_model=TeamResponse)
def read_team(*, team_id: int, include_heroes: bool = False, session: Session = Depends(get_session)):
    model_class = TeamRead
    if include_heroes:
        model_class = TeamReadWithHeroes
    team = session.get(Team, team_id)
    if not team:
        raise HTTPException(status_code=404, detail="Team not found")
    return model_class.model_validate(team)