# MiddlewareContainer

**Kind:** Class

**Source:** [`packages/core/middleware/container.ts`](https://github.com/nestjs/nest/blob/master/packages/core/middleware/container.ts#L8)

**Part of:** [Core](subsystem-packages-core)

`MiddlewareContainer` stores middleware providers and their route-level configurations for the application. It maintains collections keyed by injection token and module key, allowing the middleware runtime to resolve middleware instances and apply configurations during request pipeline setup.

## Methods

| Method | Signature | Returns |
|---|---|---|
| `getMiddlewareCollection` | `getMiddlewareCollection(moduleKey: string)` | `Map<InjectionToken, InstanceWrapper>` |
| `getConfigurations` | `getConfigurations()` | `Map<string, Set<MiddlewareConfiguration>>` |
| `insertConfig` | `insertConfig(configList: MiddlewareConfiguration[], moduleKey: string)` | `void` |

## Diagram

```mermaid
graph LR
  Module[Module registration] --> Config[MiddlewareConfiguration]
  Config --> Insert[MiddlewareContainer.insertConfig]
  Insert --> ConfigMap["configurations: Map<moduleKey, Set<MiddlewareConfiguration>>"]
  Providers[Middleware providers] --> MiddlewareMap["middleware: Map<InjectionToken, InstanceWrapper>"]
  MiddlewareMap --> Resolver[Middleware resolver]
  ConfigMap --> Resolver
  Resolver --> Pipeline[HTTP middleware pipeline]
```

## Usage

```ts
import { MiddlewareContainer } from '@nestjs/core/middleware/container';
import { RequestMethod } from '@nestjs/common';
import type { MiddlewareConfiguration } from '@nestjs/common/interfaces/middleware';

const middlewareContainer = new MiddlewareContainer(applicationConfig);

const configuration: MiddlewareConfiguration = {
  middleware: [LoggerMiddleware],
  forRoutes: [
    {
      path: 'users',
      method: RequestMethod.ALL,
    },
  ],
};

const moduleKey = 'UsersModule';

middlewareContainer.insertConfig([configuration], moduleKey);

const configurations = middlewareContainer.getConfigurations();
const userMiddlewareConfigs = configurations.get(moduleKey);

console.log(userMiddlewareConfigs);
```

## AI Coding Instructions

- Use `insertConfig()` to add middleware configurations so multiple configuration entries for the same module are preserved in a `Set`.
- Treat module keys as stable, unique identifiers; inconsistent keys will create separate configuration groups.
- Do not replace the maps returned by `getMiddlewareCollection()` or `getConfigurations()`; consumers depend on the container’s shared collections.
- Keep middleware provider registration and route configuration synchronized so each configured middleware can be resolved from its injection token.
- When adding configuration behavior, preserve insertion order because middleware execution order can affect request handling.