Dependency Injection

g0v0's dependency injection system is based on FastDepends, which is a standalone dependency injection library extracted from FastAPI. It allows you to declare and inject dependencies in any part of your plugin (including event listeners) in a FastAPI-like manner.

Define Dependencies

You can define a dependency function to create and return the service instance you need. For example:

async def my_plugin_service():
    # Create and return the service instance needed by the plugin
    return MyPluginService()

Inject Dependencies

You can use Depends in event listeners to inject this dependency:

from app.plugins import listen
from fast_depends import Depends


@listen
async def on_some_event(my_service: MyPluginService = Depends(my_plugin_service)):
    await my_service.do_something()

Warning

Import Depends from fast_depends, not from fastapi.

Tip

The event is also a dependency, so you can inject it in event listeners without using Depends:

@listen
async def on_some_event(event: MyCustomEvent, my_service: MyPluginService = Depends(my_plugin_service)):
    print(f"Received event: {event.message}")
    await my_service.do_something()

Built-in Dependency Injection

g0v0 also provides some built-in dependency injections to help you access core services and resources. For example, you can inject Database to perform database operations:

from app.dependencies.database import Database   # AsyncSession


@listen
async def on_some_event(db: Database):
    # Use db for database operations
    ...

Dependencies provided by g0v0 are implemented using both FastAPI's Depends and FastDepends' Depends, so you can also use them in API endpoints.

See Built-in Dependency Injection to learn more about available dependency injections.