dj-services

Services + svcs Dependency Injection

This project separates Django's framework concerns from business logic using a plain service layer, wired with the svcs service locator. The result:

• Views are one-liners. They pull a wired service and call a method.
• Services contain the business logic. They take repositories (and other services) via __init__, call methods on them, and return DTOs.
• Services never import Django ORM or models. Every test can run without a database.
• One registry, one get[T]() helper. The same call works in views, tasks, commands, anywhere.

Why svcs Instead of Module-Level Singletons or a Custom Container

• svcs is a tiny, typed, well-maintained service locator — no metaclasses, no decorators, no framework coupling.
• Factories are lazy: a service is constructed only when something asks for it.
• Generic get[T](type[T]) -> T preserves types through IDE/type-checker inference.
• Swapping an implementation in tests is a one-line factory override.
• No import-order gymnastics: the registry is populated once at startup and then used by name.

The Registry — src/project/services.py

import svcs

from products.repositories.product import ProductRepository
from products.services.product import ProductService
from orders.repositories.order import OrderRepository
from orders.services.order import OrderService

registry = svcs.Registry()


# --- Services (factories pull repos from the container) ------------------
def _product_service_factory(container: svcs.Container) -> ProductService:
    repo = container.get(ProductRepository)
    return ProductService(repo)


def _order_service_factory(container: svcs.Container) -> OrderService:
    repo = container.get(OrderRepository)
    product_repo = container.get(ProductRepository)
    return OrderService(repo, product_repo)


def register_services(registry: svcs.Registry) -> None:
    """Register every real factory. Tests re-run this to restore overrides."""
    # --- Repositories -----------------------------------------------------
    registry.register_factory(ProductRepository, ProductRepository)
    registry.register_factory(OrderRepository, OrderRepository)
    # --- Services ---------------------------------------------------------
    registry.register_factory(ProductService, _product_service_factory)
    registry.register_factory(OrderService, _order_service_factory)


register_services(registry)


def get[T](service_type: type[T]) -> T:
    """Resolve a service from the registry. Works anywhere — views, tasks, commands, tests."""
    return svcs.Container(registry).get(service_type)