1_dependencies.py

from os import environ

from sqlalchemy.ext.asyncio import AsyncEngine, create_async_engine

# we first define a dependency. The dependency is a function or method (async or sync) whose return value will be injected

def create_postgres_connection() -> AsyncEngine:
    postgres_connection_string = environ.get("POSTGRES_CONNECTION_STRING", "")
    if not postgres_connection_string:
        raise ValueError("Missing ENV Variable POSTGRES_CONNECTION_STRING")
    return create_async_engine(postgres_connection_string)
  

2_route_handler.py

from sqlalchemy.ext.asyncio import AsyncEngine
from starlite import get


# a dependency is a kwarg - in this case "connection". The dependency needs to be mapped to the kwarg on some 
# of the application. 
@get("/some-path")
async def my_route_handler(connection: AsyncEngine) -> None:
  ...

3_main.py

from starlite import Starlite, Provide

from dependencies import create_postgres_connection
from route_handler import my_route_handler


# when instantiating the app we declare the dependency, mapping it to the key "connection". We also cache it, so the
# engine will be created once and not on every call. 
app = Starlite(
  route_handlers=[my_route_handler], 
  dependencies={ 
    "connection": Provide(create_postgres_connection, use_cache=True) 
  },
)