Read One Model with FastAPI

Let's now add a path operation to read a single model to our FastAPI application.

Path Operation for One Hero

Let's add a new path operation to read one single hero.

We want to get the hero based on the id, so we will use a path parameter hero_id.

Info

If you need to refresh how path parameters work, including their data validation, check the FastAPI docs about Path Parameters.

from typing import List, Optional

from fastapi import FastAPI, HTTPException
from sqlmodel import Field, Session, SQLModel, create_engine, select

# Code here omitted 👈

@app.get("/heroes/{hero_id}", response_model=HeroRead)
def read_hero(hero_id: int):
    with Session(engine) as session:
        hero = session.get(Hero, hero_id)
        if not hero:
            raise HTTPException(status_code=404, detail="Hero not found")
        return hero

👀 Full file preview

from typing import List, Optional

from fastapi import FastAPI, HTTPException
from sqlmodel import Field, Session, SQLModel, create_engine, select


class HeroBase(SQLModel):
    name: str = Field(index=True)
    secret_name: str
    age: Optional[int] = Field(default=None, index=True)


class Hero(HeroBase, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)


class HeroCreate(HeroBase):
    pass


class HeroRead(HeroBase):
    id: int


sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"

connect_args = {"check_same_thread": False}
engine = create_engine(sqlite_url, echo=True, connect_args=connect_args)


def create_db_and_tables():
    SQLModel.metadata.create_all(engine)


app = FastAPI()


@app.on_event("startup")
def on_startup():
    create_db_and_tables()


@app.post("/heroes/", response_model=HeroRead)
def create_hero(hero: HeroCreate):
    with Session(engine) as session:
        db_hero = Hero.model_validate(hero)
        session.add(db_hero)
        session.commit()
        session.refresh(db_hero)
        return db_hero


@app.get("/heroes/", response_model=List[HeroRead])
def read_heroes():
    with Session(engine) as session:
        heroes = session.exec(select(Hero)).all()
        return heroes


@app.get("/heroes/{hero_id}", response_model=HeroRead)
def read_hero(hero_id: int):
    with Session(engine) as session:
        hero = session.get(Hero, hero_id)
        if not hero:
            raise HTTPException(status_code=404, detail="Hero not found")
        return hero

For example, to get the hero with ID 2 we would send a GET request to:

/heroes/2

Handling Errors

Then, because FastAPI already takes care of making sure that the hero_id is an actual integer, we can use it directly with Hero.get() to try and get one hero by that ID.

But if the integer is not the ID of any hero in the database, it will not find anything, and the variable hero will be None.

So, we check it in an if block, if it's None, we raise an HTTPException with a 404 status code.

And to use it, we first import HTTPException from fastapi.

This will let the client know that they probably made a mistake on their side and requested a hero that doesn't exist in the database.

from typing import List, Optional

from fastapi import FastAPI, HTTPException
from sqlmodel import Field, Session, SQLModel, create_engine, select

# Code here omitted 👈

@app.get("/heroes/{hero_id}", response_model=HeroRead)
def read_hero(hero_id: int):
    with Session(engine) as session:
        hero = session.get(Hero, hero_id)
        if not hero:
            raise HTTPException(status_code=404, detail="Hero not found")
        return hero

👀 Full file preview

from typing import List, Optional

from fastapi import FastAPI, HTTPException
from sqlmodel import Field, Session, SQLModel, create_engine, select


class HeroBase(SQLModel):
    name: str = Field(index=True)
    secret_name: str
    age: Optional[int] = Field(default=None, index=True)


class Hero(HeroBase, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)


class HeroCreate(HeroBase):
    pass


class HeroRead(HeroBase):
    id: int


sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"

connect_args = {"check_same_thread": False}
engine = create_engine(sqlite_url, echo=True, connect_args=connect_args)


def create_db_and_tables():
    SQLModel.metadata.create_all(engine)


app = FastAPI()


@app.on_event("startup")
def on_startup():
    create_db_and_tables()


@app.post("/heroes/", response_model=HeroRead)
def create_hero(hero: HeroCreate):
    with Session(engine) as session:
        db_hero = Hero.model_validate(hero)
        session.add(db_hero)
        session.commit()
        session.refresh(db_hero)
        return db_hero


@app.get("/heroes/", response_model=List[HeroRead])
def read_heroes():
    with Session(engine) as session:
        heroes = session.exec(select(Hero)).all()
        return heroes


@app.get("/heroes/{hero_id}", response_model=HeroRead)
def read_hero(hero_id: int):
    with Session(engine) as session:
        hero = session.get(Hero, hero_id)
        if not hero:
            raise HTTPException(status_code=404, detail="Hero not found")
        return hero

Return the Hero

Then, if the hero exists, we return it.

And because we are using the response_model with HeroRead, it will be validated, documented, etc.

from typing import List, Optional

from fastapi import FastAPI, HTTPException
from sqlmodel import Field, Session, SQLModel, create_engine, select

# Code here omitted 👈

@app.get("/heroes/{hero_id}", response_model=HeroRead)
def read_hero(hero_id: int):
    with Session(engine) as session:
        hero = session.get(Hero, hero_id)
        if not hero:
            raise HTTPException(status_code=404, detail="Hero not found")
        return hero

👀 Full file preview

from typing import List, Optional

from fastapi import FastAPI, HTTPException
from sqlmodel import Field, Session, SQLModel, create_engine, select


class HeroBase(SQLModel):
    name: str = Field(index=True)
    secret_name: str
    age: Optional[int] = Field(default=None, index=True)


class Hero(HeroBase, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)


class HeroCreate(HeroBase):
    pass


class HeroRead(HeroBase):
    id: int


sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"

connect_args = {"check_same_thread": False}
engine = create_engine(sqlite_url, echo=True, connect_args=connect_args)


def create_db_and_tables():
    SQLModel.metadata.create_all(engine)


app = FastAPI()


@app.on_event("startup")
def on_startup():
    create_db_and_tables()


@app.post("/heroes/", response_model=HeroRead)
def create_hero(hero: HeroCreate):
    with Session(engine) as session:
        db_hero = Hero.model_validate(hero)
        session.add(db_hero)
        session.commit()
        session.refresh(db_hero)
        return db_hero


@app.get("/heroes/", response_model=List[HeroRead])
def read_heroes():
    with Session(engine) as session:
        heroes = session.exec(select(Hero)).all()
        return heroes


@app.get("/heroes/{hero_id}", response_model=HeroRead)
def read_hero(hero_id: int):
    with Session(engine) as session:
        hero = session.get(Hero, hero_id)
        if not hero:
            raise HTTPException(status_code=404, detail="Hero not found")
        return hero

Check the Docs UI

We can then go to the docs UI and see the new path operation.

Recap

You can combine FastAPI features like automatic path parameter validation to get models by ID.