di

name	di
description	Wire classes into the Inversify DI container correctly. Use when adding new repositories, controllers, services, or middleware to the server. Use when wiring dependencies, configuring the DI container, or understanding how classes are resolved.

Inversify Dependency Injection

The monotemplate uses Inversify v7 with reflect-metadata for decorator-based dependency injection. All DI configuration lives in apps/server/src/di/container.ts, which exports a singleton container instance.

Making a Class Injectable

Every Repository, Controller, and Service class must be decorated with @injectable(). Constructor dependencies use @inject(ClassName) parameter decorators. Import the class itself (not type-only) so the class token is available at runtime.

import { injectable, inject } from "inversify";
import { SomeRepository } from "@server/repositories/SomeRepository";

@injectable()
export class SomeController {
  constructor(@inject(SomeRepository) private someRepository: SomeRepository) {}
}

Registering Bindings in container.ts

Pattern	Use case	Example
toSelf().inSingletonScope()	Classes that auto-resolve their own deps	Repositories, Controllers
toConstantValue(value)	External/constant values	PrismaClient, env-gated services
to(ConcreteClass).inSingletonScope()	Abstract to concrete	Auth factories
bind(SYMBOL).toConstantValue(value) (repeated)	Multi-bindings	Express middleware

Binding Order

Follow this order in container.ts:

// Database
container.bind(PrismaClient).toConstantValue(prisma);

// Middleware (multi-binding via Symbol token)
container.bind(EXPRESS_MIDDLEWARE).toConstantValue(helmet());
container.bind(EXPRESS_MIDDLEWARE).toConstantValue(express.json());

// Auth (abstract → concrete, with simulated mode gating)
if (isSimulated()) {
    container.bind(AuthContextFactory).to(SimulatedAuthContextFactory).inSingletonScope();
} else {
    container.bind(AuthContextFactory).to(ClerkAuthContextFactory).inSingletonScope();
}

// Repositories
container.bind(FooRepository).toSelf().inSingletonScope();

// Controllers
container.bind(FooController).toSelf().inSingletonScope();

Resolving Dependencies

• In routers/handlers: container.get(ClassName) — import both container and the class
• In server.ts: container.get(AuthContextFactory), container.getAll<T>(EXPRESS_MIDDLEWARE)
• Never destructure from a container object; always use container.get()

import { container } from "@server/di/container";
import { UsersController } from "@server/controllers/UsersController";

const result = await container.get(UsersController).getUserById(id);

Symbol Tokens (di/tokens.ts)

Used for multi-bindings where multiple values share one key (e.g., EXPRESS_MIDDLEWARE).

export const TOKEN_NAME = Symbol.for("TokenName");

Simulated / E2E Auth Gating

• __dev__/ directory code is dynamically imported inside isSimulated() checks (Bun macro)
• Never use static imports for __dev__/ code in production paths

if (isSimulated()) {
    const { SimulatedAuthContextFactory } = await import("@server/__dev__/SimulatedAuthContextFactory");
    container.bind(AuthContextFactory).to(SimulatedAuthContextFactory).inSingletonScope();
}

Nullable / Env-Gated Services

When a service depends on an env variable that may not be set, bind it as ServiceClass | null:

container.bind<StorageService | null>(StorageService).toConstantValue(
    env.SOME_KEY ? new StorageService({ ... }) : null,
);

// Resolve with explicit type annotation:
const svc = container.get<StorageService | null>(StorageService);

tsconfig Requirements

• experimentalDecorators: true and emitDecoratorMetadata: true must be set
• import "reflect-metadata" must be the first import in the entry point (index.ts)

New Entity Checklist

When adding a new Repository, Controller, or Service:

1. Add @injectable() to the class
2. Add @inject(Dep) to each constructor parameter
3. Import classes (not type-only) for injected dependencies
4. Register binding in container.ts under the appropriate section
5. In routers, resolve via container.get(ClassName)