Injecting a list of dependencies

[JarnoRFB]

Hi, thanks for the nice and well documented framework! There is one point I am currently missing. Let's say I have a class that depends on a list of other classes, I want to achieve something like the following example (written in Python 3.7)

from typing import *
from dependency_injector import containers, providers


class B:
    def __init__(self, val: int):
        self.val = val

    def __repr__(self):
        return f"B({self.val})"


class A:
    def __init__(self, bs: List[B]):
        self.bs = bs

    def __repr__(self):
        return f"A({self.bs})"


def main() -> None:
    class IocContainer(containers.DeclarativeContainer):
        bs = providers.Provider(
            list,
            providers.Factory(B, 1),
            providers.Factory(B, 2),

        )

        a = providers.Factory(
            A,
            bs,
        )

    container = IocContainer()

    print(container.a())


if __name__ == "__main__":
    main()

However, using a list of providers seems not to be possible, as the list constructor only takes a single argument, but directly instantiating a list of providers will not instantiate the providers.
What would be the way to go to inject a list of dependencies.

[mithrandir4859]

@JarnoRFB
Funnily enough I was exploring this very issue at this very moment. So, I don't know how authors intended to handle such case but it is very easy to circumvent the apparent framework limitation - just use to_list function instead of list as the first argument to your factory.

def to_list(*vargs):
    return vargs

[JarnoRFB]

@yandrieiev thanks for the hint. One could also generalize this for other types that take iterables in their contructor.

from typing import *

from dependency_injector import containers, providers


class B:
    def __init__(self, val: int):
        self.val = val

    def __repr__(self):
        return f"B({self.val})"


class A:
    def __init__(self, bs: List[B]):
        self.bs = bs

    def __repr__(self):
        return f"A({self.bs})"


def collection_of(collection_type, *args):
    return collection_type(args)


def main() -> None:
    class IocContainer(containers.DeclarativeContainer):
        bs = providers.Factory(collection_of, list, providers.Factory(B, 1), providers.Factory(B, 2))

        a = providers.Factory(A, bs)

    container = IocContainer()

    print(container.a())


if __name__ == "__main__":
    main()

Probably would be a good idea to document this.

[rmk135]

Hello gentlemen,

I would adapt particular case to:

from typing import *

from dependency_injector import containers, providers


class B:
    def __init__(self, val: int):
        self.val = val

    def __repr__(self):
        return f"B({self.val})"


class A:
    def __init__(self, *bs: List[B]):
        self.bs = bs

    def __repr__(self):
        return f"A({self.bs})"


def main() -> None:
    class IocContainer(containers.DeclarativeContainer):

        a = providers.Factory(
            A,
            providers.Factory(B, 1),
            providers.Factory(B, 2),
        )

    container = IocContainer()

    print(container.a())


if __name__ == "__main__":
    main()

The solution is not identical to provided ones. There are two differences:

1. It limits A from having other positional arguments.
2. Context positional arguments will be appended (details at bullet #4 at http://python-dependency-injector.ets-labs.org/providers/factory.html#factory-providers-and-init-injections).

I like the workaround proposed by @yandrieiev and collection_of(...) solution looks accurate @JarnoRFB . This feature is a good release candidate. I will consider building it in.

Roman

[rmk135]

@JarnoRFB @yandrieiev

I have created a new provider - List. It can be used for injecting a list of values. It's as simple as this:

dispatcher_factory = providers.Factory(
    Dispatcher,
    modules=providers.List(
        providers.Factory(Module, name='m1'),
        providers.Factory(Module, name='m2'),
    ),
)

The original example from this issue now can look like this:

class IocContainer(containers.DeclarativeContainer):
    bs = providers.List(
        providers.Factory(B, 1),
        providers.Factory(B, 2),

    )

    a = providers.Factory(
        A,
        bs,
    )

List provider is available in version 3.16.0. Version 3.16.0 is published on PyPI. You're welcome to upgrade.

Roman