Framework Integrations
In addition to the binding decorators lagom provides a number of integrations to popular web frameworks.
Starlette
To make integration with starlette simpler an integration is provided that can generate starlette routes.
Starlette endpoints are defined in the normal way. Any extra arguments are then provided by the container:
from lagom import injectable
async def homepage(request, db: DBConnection = injectable):
user = db.fetch_data_for_user(request.user)
return PlainTextResponse(f"Hello {user.name}")
container = Container()
container[DBConnection] = DB("DSN_CONNECTION_GOES_HERE")
with_deps = StarletteIntegration(container)
routes = [
# This function takes the same arguments as starlette.routing.Route
with_deps.route("/", endpoint=homepage),
]
app = Starlette(routes=routes)
FastAPI
FastAPI already provides a method for dependency injection however if you'd like to use lagom instead an integration is provided.
Calling the method .depends will provide a dependency in the format
that FastAPI expects:
container = Container()
container[DBConnection] = DB("DSN_CONNECTION_GOES_HERE")
app = FastAPI()
deps = FastApiIntegration(container)
@app.get("/")
async def homepage(request, db = deps.depends(DBConnection)):
# 👆 This is a lagom method that works like FastAPI's
user = db.fetch_data_for_user(request.user)
return PlainTextResponse(f"Hello {user.name}")
Access the request
The fast api automatically binds the active request to the container. This enables the following definitions:
from starlette.requests import Request
class SomeExtendedRequest:
def __init(self, req: Request, db: Database):
pass
Each time SomeExtendedRequest is created the correct Request
object will be passed in.
Swapping for mocks when using the test client
Lagom encourages testing with dependencies manually passed to the code under test.
However, when testing using the test client dependencies will be constructed using
the lagom container. For this reason you may want to swap out certain dependencies.
The fastapi integration has a method override_for_test which returns a ContextManager
that can temporarily edit the dependency injection container.
def test_something():
client = TestClient(app)
with deps.override_for_test() as test_container:
# FooService is an external API so mock it during test
test_container[FooService] = Mock(FooService)
response = client.get("/")
assert response.status_code == 200
Request level singletons
When constructing the integration a list of types can be passed for request level singletons. Each of these types will only be constructed once per request:
deps = FastApiIntegration(container, request_singletons=[SomeClass])
Request level singletons - with clean up
In addition to the request level singletons it's also possible to define types that are a singleton over the lifetime of the request and call some clean up code once the request has been handled. This is implemented using regular python context managers.
When setting up the integration a list of types using context managers can be provided.
deps = FastApiIntegration(container, request_context_singletons=[SomeClass])
When a dependency of type SomeClass is required lagom looks for ContextManager[SomeClass].
This can be defined in the container in two ways. Either with a generator and the context manager decorator:
@context_dependency_definition(container)
def my_constructor() -> Iterator[SomeResource]:
try:
yield SomeResource()
finally:
# TODO: do some tidy up now the request has finished
pass
Or alternatively if a ContextManager already exists for the class this can be used:
class SomeResourceManager:
def __enter__(self):
return SomeResource()
def __exit__(self, exc_type, exc_val, exc_tb):
# TODO: do some tidy up now the request has finished
pass
container[ContextManager[SomeResource]] = SomeResourceManager
Flask API
An integration is provided for flask. It takes the flask app
and a container then provides a wrapped route decorator to use:
app = Flask(__name__)
container[Database] = Singleton(lambda: Database("connection details"))
app_with_deps = FlaskIntegration(app, container)
@app_with_deps.route("/save_it/<string:thing_to_save>", methods=['POST'])
def save_to_db(thing_to_save, db: Database = injectable):
db.save(thing_to_save)
return 'saved'
The decorator leaves the original function unaltered so it can be used directly in tests.
Flask Blueprints
Experimental support is provided for flask blueprints. See documentation here: Flask blueprint Docs
Django
A django integration is currently under beta in the experimental module. See documentation here: Django Integration Docs
Click
A click integration is currently under beta in the experimental module. See documentation here: Click Integration Docs(experimental.md#click)