DependenciesScanner

Kind: Class

Source: packages/core/scanner.ts

Part of: Core

DependenciesScanner discovers an application’s module tree and reflects Nest metadata for imports, providers, controllers, exports, and dynamic module configuration. It populates the NestContainer during application initialization so the dependency injection system can resolve modules and their registered components.

Methods

moduleDefinition,
lazy,
scope = [],
ctxRegistry = [],
overrides = [],

}: ModulesScanParameters)|Promise<Module[]>| |insertModule|insertModule(moduleDefinition: any, scope: Type[])|Promise< | { moduleRef: Module; inserted: boolean; } | undefined >| |scanModulesForDependencies|scanModulesForDependencies(modules: Map<string, Module>)|void| |reflectImports|reflectImports(module: Type, token: string, context: string)|void| |reflectProviders|reflectProviders(module: Type, token: string)|void| |reflectControllers|reflectControllers(module: Type, token: string)|void| |reflectDynamicMetadata|reflectDynamicMetadata(cls: Type, token: string)|void| |reflectExports|reflectExports(module: Type, token: string)|void| |reflectInjectables|reflectInjectables(component: Type, token: string, metadataKey: string)|void| |reflectParamInjectables|reflectParamInjectables(component: Type, token: string, metadataKey: string)|void| |reflectKeyMetadata|reflectKeyMetadata(component: Type, key: string, methodKey: string)|{ methodKey: string; metadata: any } | undefined| |calculateModulesDistance|calculateModulesDistance()|void| |insertImport|insertImport(related: any, token: string, context: string)|void| |isCustomProvider|isCustomProvider(provider: Provider)|provider is | ClassProvider | ValueProvider | FactoryProvider | ExistingProvider| |insertProvider|insertProvider(provider: Provider, token: string)|void| |insertInjectable|insertInjectable(injectable: Type | object, token: string, host: Type, subtype: EnhancerSubtype, methodKey: string)|void| |insertExportedProviderOrModule|insertExportedProviderOrModule(toExport: ForwardReference | DynamicModule | Type, token: string)|void| |insertController|insertController(controller: Type, token: string)|void| |reflectMetadata|reflectMetadata(metadataKey: string, metatype: Type)|T[]| |registerCoreModule|registerCoreModule(overrides: ModuleOverride[])|void| |addScopedEnhancersMetadata|addScopedEnhancersMetadata()|void| |applyApplicationProviders|applyApplicationProviders()|void| |getApplyProvidersMap|getApplyProvidersMap()|{ [type: string]: Function }| |getApplyRequestProvidersMap|getApplyRequestProvidersMap()|{ [type: string]: Function }| |isDynamicModule|isDynamicModule(module: Type | DynamicModule)|module is DynamicModule` |

Where it refuses work

• DependenciesScanner stops the work with UndefinedModuleException when innerModule === undefined.
• DependenciesScanner stops the work with InvalidModuleException when !innerModule.
• DependenciesScanner stops the work with InvalidClassModuleException when this.isInjectable(moduleToAdd).
• DependenciesScanner stops the work with InvalidClassModuleException when this.isController(moduleToAdd).
• DependenciesScanner stops the work with InvalidClassModuleException when this.isExceptionFilter(moduleToAdd).
• DependenciesScanner stops the work with CircularDependencyException when isUndefined(related).

Diagram

mermaid
graph LR
  A[Root Module] --> B[DependenciesScanner.scan]
  B --> C[scanForModules]
  C --> D[insertModule]
  D --> E[NestContainer]
  B --> F[scanModulesForDependencies]
  F --> G[reflectImports]
  F --> H[reflectProviders]
  F --> I[reflectControllers]
  F --> J[reflectDynamicMetadata]
  F --> K[reflectExports]
  F --> L[reflectInjectables]
  G --> E
  H --> E
  I --> E
  J --> E
  K --> E
  L --> E

Usage

ts
import { DependenciesScanner } from '@nestjs/core/scanner';
import { NestContainer } from '@nestjs/core/injector/container';
import { MetadataScanner } from '@nestjs/core/metadata-scanner';
import { GraphInspector } from '@nestjs/core/inspector/graph-inspector';
import { ApplicationConfig } from '@nestjs/core/application-config';

import { AppModule } from './app.module';

// These dependencies are normally created and managed by Nest's core bootstrap flow.
declare const container: NestContainer;
declare const metadataScanner: MetadataScanner;
declare const graphInspector: GraphInspector;
declare const applicationConfig: ApplicationConfig;

async function scanApplicationModules() {
  const scanner = new DependenciesScanner(
    container,
    metadataScanner,
    graphInspector,
    applicationConfig,
  );

  await scanner.scan(AppModule);

  // The container now includes discovered modules, providers, and controllers.
}

AI Coding Instructions

• Treat DependenciesScanner as framework bootstrap infrastructure; application code should normally rely on NestFactory rather than instantiate it directly.
• Preserve the scanning order: register modules before reflecting imports, providers, controllers, exports, and injectable metadata.
• When adding metadata reflection behavior, ensure discovered components are registered through NestContainer so dependency resolution remains consistent.
• Account for dynamic modules and module overrides when changing scanForModules() or insertModule().
• Avoid duplicate module registration; use the inserted result from insertModule() when subsequent work should only run for newly added modules.

Relationships

• IMPORTS → DynamicModule
• IMPORTS → ForwardReference
• IMPORTS → Provider
• IMPORTS → CATCH_WATERMARK
• IMPORTS → CONTROLLER_WATERMARK
• IMPORTS → ENHANCER_KEY_TO_SUBTYPE_MAP
• IMPORTS → EXCEPTION_FILTERS_METADATA
• IMPORTS → EnhancerSubtype
• IMPORTS → GUARDS_METADATA
• IMPORTS → INJECTABLE_WATERMARK
• IMPORTS → INTERCEPTORS_METADATA
• IMPORTS → MODULE_METADATA
• IMPORTS → PIPES_METADATA
• IMPORTS → ROUTE_ARGS_METADATA
• IMPORTS → CanActivate
• IMPORTS → ClassProvider
• IMPORTS → Controller
• IMPORTS → ExceptionFilter
• IMPORTS → ExistingProvider
• IMPORTS → FactoryProvider
• IMPORTS → Injectable
• IMPORTS → InjectionToken
• IMPORTS → NestInterceptor
• IMPORTS → PipeTransform
• IMPORTS → Scope
• IMPORTS → Type
• IMPORTS → ValueProvider
• IMPORTS → isFunction
• IMPORTS → isNil
• IMPORTS → isUndefined

Used by

1 reference from 1 file. Each is a place in this repository where the symbol is actually used — go read one rather than trusting an example.

Imported by (1)

• TestingModuleOptions — packages/testing/testing-module.builder.ts:29