Module

A module is a class that is annotated with the @Module() decorator. This decorator provides metadata that Nest uses to organize and manage the application structure efficiently.

// cats/cats.module.ts
import { Module } from "@nestjs/common";
import { CatsController } from "./cats.controller";
import { CatsService } from "./cats.service";

@Module({
  controllers: [CatsController],
  providers: [CatsService],
  exports: [CatsService],
})
export class CatsModule {}

// app.module.ts
import { Module } from "@nestjs/common";
import { CatsModule } from "./cats/cats.module";

@Module({
  imports: [CatsModule],
})
export class AppModule {}

Re-Exporting

@Module({
  imports: [CommonModule],
  exports: [CommonModule],
})
export class CoreModule {}

Dependency injection

import { Module } from "@nestjs/common";
import { CatsController } from "./cats.controller";
import { CatsService } from "./cats.service";

@Module({
  controllers: [CatsController],
  providers: [CatsService],
})
export class CatsModule {
  constructor(private catsService: CatsService) {}
}

Global Modules

When we want to provide a set of providers which should be available everywhere out-of-the-box (e.g., helpers, database connections, etc.), make the module global with the @Global() decorator.

import { Module, Global } from "@nestjs/common";
import { CatsController } from "./cats.controller";
import { CatsService } from "./cats.service";

@Global()
@Module({
  controllers: [CatsController],
  providers: [CatsService],
  exports: [CatsService],
})
export class CatsModule {}

Dynamic modules

Dynamic modules in Nest allow us to create modules that can be configured at runtime.

import { Module, DynamicModule } from "@nestjs/common";
import { createDatabaseProviders } from "./database.providers";
import { Connection } from "./connection.provider";

@Module({
  providers: [Connection],
  exports: [Connection],
})
export class DatabaseModule {
  static forRoot(entities = [], options?): DynamicModule {
    const providers = createDatabaseProviders(options, entities);
    return {
      module: DatabaseModule,
      providers: providers,
      exports: providers,
    };
  }
}