FastAPI service with and without dependencies

fastapi_dependencies.py

"""
A simple contrived example of a FastAPI application that heavily uses
the FastAPI dependency injection system.

Sample request http://127.0.0.1:9876/tasks?user_id=123456
returns [{"id":1,"name":"Task 1","user":{"id":123456,"name":"John Doe"}}]

Dependency tree:

get_me()
    current_user()
        Cache.get_user_by_id()
        UserService.get_user_by_id()


get_tasks()
    user_tasks()
        current_user()
            Cache.get_user_by_id()
            UserService.get_user_by_id()
"""

import fastapi
from fastapi import Depends
from pydantic import BaseModel

api = fastapi.FastAPI()


class User(BaseModel):
    id: int
    name: str


class Task(BaseModel):
    id: int
    name: str
    user: User


class UserService:
    def get_user_by_id(self, user_id: int) -> User | None:
        return User(id=user_id, name="John Doe")


class Cache:
    def get_user_by_id(self, user_id: int) -> User | None:
        return None


def current_user(
    user_id: int,
    user_service: UserService = Depends(UserService),
    cache: Cache = Depends(Cache),
):
    user = cache.get_user_by_id(user_id)
    if user is None:
        user = user_service.get_user_by_id(user_id)
    return user


def user_tasks(user: User = Depends(current_user)):
    return [Task(id=1, name="Task 1", user=user)]


@api.get("/me")
def get_me(user: User = Depends(current_user)):
    return user


@api.get("/tasks")
def get_tasks(tasks: list[Task] = Depends(user_tasks)):
    return tasks


if __name__ == "__main__":
    import uvicorn

    uvicorn.run("fastapi_dependencies:api", host="127.0.0.1", port=9876, reload=True)

fastapi_no_dependencies.py

"""
A simple contrived example of a FastAPI application that doesn't use depoendencies.

Sample request http://127.0.0.1:9876/tasks?user_id=123456
returns [{"id":1,"name":"Task 1","user":{"id":123456,"name":"John Doe"}}]
"""

import fastapi
from pydantic import BaseModel

api = fastapi.FastAPI()


class User(BaseModel):
    id: int
    name: str


class Task(BaseModel):
    id: int
    name: str
    user: User


class UserService:
    def get_user_by_id(self, user_id: int) -> User | None:
        return User(id=user_id, name="John Doe")


class Cache:
    def get_user_by_id(self, user_id: int) -> User | None:
        return None


def current_user(
    user_id: int,
    user_service: UserService,
    cache: Cache,
):
    user = cache.get_user_by_id(user_id)
    if user is None:
        user = user_service.get_user_by_id(user_id)
    return user


def user_tasks(user: User):
    return [Task(id=1, name="Task 1", user=user)]


@api.get("/me")
def get_me(user_id: int):
    user_service = UserService()
    cache = Cache()
    user = current_user(user_id, user_service, cache)
    return user


@api.get("/tasks")
def get_tasks(user_id: int):
    user_service = UserService()
    cache = Cache()
    user = current_user(user_id, user_service, cache)
    tasks = user_tasks(user)
    return tasks


if __name__ == "__main__":
    import uvicorn

    uvicorn.run("fastapi_no_dependencies:api", host="127.0.0.1", port=9875, reload=True)

fastapi_no_di.py

"""
A simple contrived example of a FastAPI application that doesn't use depoendencies.

Sample request http://127.0.0.1:9876/tasks?user_id=123456
returns [{"id":1,"name":"Task 1","user":{"id":123456,"name":"John Doe"}}]
"""

import fastapi
from pydantic import BaseModel

api = fastapi.FastAPI()


class User(BaseModel):
    id: int
    name: str


class Task(BaseModel):
    id: int
    name: str
    user: User


class UserService:
    def get_user_by_id(self, user_id: int) -> User | None:
        return User(id=user_id, name="John Doe")


class Cache:
    def get_user_by_id(self, user_id: int) -> User | None:
        return None


cache = Cache()
user_service = UserService()


def current_user(user_id: int):
    user = cache.get_user_by_id(user_id)
    if user is None:
        user = user_service.get_user_by_id(user_id)
    return user


def user_tasks(user_id: int):
    user = current_user(user_id)
    return [Task(id=1, name="Task 1", user=user)]


@api.get("/me")
def get_me(user_id: int):
    user = current_user(user_id)
    return user


@api.get("/tasks")
def get_tasks(user_id: int):
    tasks = user_tasks(user_id)
    return tasks


if __name__ == "__main__":
    import uvicorn

    uvicorn.run("fastapi_no_dependencies:api", host="127.0.0.1", port=9874, reload=True)