Classes and dependency inversion principle

[mapeveri]

I have an app using hexagonal architecture and i'm trying to apply the dependency inversion principle with Depends as dependency injection. I have this:

# infraestructure/countries.py are my endpoints
@router.get('/')
async def all_countries(all_countries: AllCountries = Depends(AllCountries)) -> List[Country]:
    countries = await all_countries.handle()
    return ResponseModel(countries)

# infraestructure/mongo_country_repository.py 
# is my mongo repository to access to the collection
class MongoCountryRepository(CountryRepository, MongoBaseRepository):
    manager: DatabaseManager
    model: Country
    collection: str

    def __init__(self, manager: DatabaseManager = Depends(get_database)) -> None:
        self.manager = manager
        self.model = Country
        self.collection = 'countries'

    async def get(self, id: str) -> Country:
        return await self.get_record(id)

    async def all(self) -> List[Country]:
        return await self.get_all()

    async def create(self, record: Country) -> Country:
        return await self.insert_record(record)

And I have my application service, in another folder (not infrastructure)

# application/all_countries.py
# is my application service for get the countries
class AllCountries(Service):
    repository: CountryRepository

    def __init__(self, repository: CountryRepository) -> None:
        self.repository = repository

    async def handle(self) -> List[Country]:
        return await self.repository.all()

This example not is 100% real, because the logic is very easy, but is for demonstrate my problem.

I would like that the application service know nothing about fastapi, and I'm trying all dependencies manage to in infrastructure.
My question is how can set the repository MongoCountryRepository to AllCountries application service?. CountryRepository is an interface.

[teamhide]

Maybe it looks like part of clean architecture. I also had the same concerns before and implement dependency injection library. How about use it? https://github.com/teamhide/pythondi

[ChilloManiac]

Would love to be able to accommodate this case in native FastApi

[tiangolo]

You probably need a different tool, the dependency injection system in FastAPI is very simple and it's designed to be interested and handled by FastAPI. You probably need something else for your internal dependency system and then combine that with FastAPI.