How to inject a dependency in a Controller class?

[l3t2st1r]

I have several controllers with some common features so I want them to convert them into subclasses and move the common functionality to a parent class. A child controller would look like this:

... imports
class CategoryController(BaseEndpoint):
    _path = f"{BASE_PATH}category"

    @get(path=_path
              + "/category/{category:str}"
         )
      async def get_dut(
            self, category: int
    ) -> list:
       # I want to inject _db_handler in the parent class
        return await self._db_handler.get_categories(category)
        )

so the parent class would look like this:

class BaseEndpoint(Controller):
       _db_handler = ???

using dependencies = {"_db_handler": Provide(db_handler)} does not work.

[provinzkraut]

Controllers and dependencies don't work like that. Dependencies are only injected into other dependencies or route handlers. Controller instances are also created once, not for each request.

Is there a reason you can't / don't want to use normal dependency injection here?
E.g. just doing

class CategoryController(BaseEndpoint):
    _path = f"{BASE_PATH}category"

    @get(path=_path
              + "/category/{category:str}"
         )
      async def get_dut(
            self, category: int, db_handler
    ) -> list:
        return await db_handler.get_categories(category)
        )

[l3t2st1r]

Hello @provinzkraut , what you did is exactly what I have already. The point is that I would like to inject the dependency in a parent class, since my controllers have a lot of shared functionality. And so I did this:

In My module init.py

...
 dependencies={
        "db_hanlder": Provide(get_elastic_search_wrapper),
...

and in any of my controllers I can do this (notice the injection in the method):

...
class XXXController(Controller):
    _path = "/api/content/v1/xxx"
    _logger: logging.Logger = get_logger(__name__)

    @get(path=_path + "/gte/{gte:str}/lte/{lte:str}")
    async def get_xxx(self, db_hanlder: SearchInDatabase, gte: str, lte: str) -> list:
        self._logger.info("GET {} with {}".format(self._path, {gte, lte}))
		return db_hanlder.get_unique_entries("dut", {"gte": gte, "lte": lte})
...

it works perfectly fine and the dependency gets into the method with no problem at all.
Since I have several controllers, I would like to have a parent class where I can inject the dependency once and reuse. So I did:

class XXXController(BaseController):
    _path = "/api/content/v1/xxx"
    _logger: logging.Logger = get_logger(__name__)

    @get(path=_path + "/gte/{gte:str}/lte/{lte:str}")
	# removed the dependency call
    async def get_xxx(self, gte: str, lte: str) -> list:
        self._logger.info("GET {} with {}".format(self._path, {gte, lte}))
		# where self.db_hanlder is a member variable injected in the base controller
		return self.db_hanlder.get_unique_entries("dut", {"gte": gte, "lte": lte})

And the base controller

class BaseController(Controller)
	db_handler

# I don't know what to do here, nothing seems to work
# 1. Using the db_hanlder variable in a method as in the example above did not work
# 2. "Dependencies" does not work
dependencies = {"db_handler": Provide(get_db_handler)}
# Using __init__ does not work, because the name db_hanlder is not available

I hope this example is a little bit clearer. Excuse the lack of code, but I don't really know how to write it.
Thanks a lot for your help.

[sinisaos]

@l3t2st1r I'm sorry if I didn't understand your request well (I'm also not a Litestar expert and I don't know if this is a good approach), but you can use super() to use the argument of the parent controller in the child controllers. Something like this

Example code

from litestar import Litestar, Controller, get
from litestar.di import Provide


async def str_fn() -> str:
    return "Dependency example"


class BaseController(Controller):
    path = "/"
    dependencies = {"db_handler": Provide(str_fn)}

    @get("parent")
    async def parent_get(self) -> str:
        return "Parent controller"


class ChildController(BaseController):
    path = "/child/"

    def __init__(self, owner):
        super().__init__(owner)

    @get("child")
    async def child_get(self) -> str:
        # parent dependencies using super()
        parent_dependencies = self.dependencies.get("db_handler")
        # prints Dependency example
        print(await parent_dependencies.dependency())
        return "Child controller"


class OtherController(BaseController):
    path = "/other/"

    def __init__(self, owner):
        super().__init__(owner)

    @get("other")
    async def other_get(self) -> str:
        # parent dependencies using super()
        parent_dependencies = self.dependencies.get("db_handler")
        # prints Dependency example
        print(await parent_dependencies.dependency())
        return "Other controller"


app = Litestar(
    route_handlers=[
        BaseController,
        ChildController,
        OtherController,
    ]
)

Again, sorry if I missed your point.

[provinzkraut]

@l3t2st1r I'm still not sure why you want to provide the dependency via a class var. What exactly is the issue with just providing it via the dependencies attribute on the controller?

[l3t2st1r]

Hi @provinzkraut the issue is that I cannot make it work, the dependency just do not get injected.