Modules

Overview

A module is a class annotated with a @Module() decorator. The @Module() decorator provides metadata that organizes the application structure. Modules encapsulate related functionality and follow the NestJS module pattern.

Module Structure

A typical module in MBC CQRS Serverless includes:

import { Module } from '@nestjs/common';
import { CommandModule } from '@mbc-cqrs-serverless/core';

import { CatController } from './cat.controller';
import { CatService } from './cat.service';
import { CatDataSyncRdsHandler } from './handler/cat-rds.handler';

@Module({
  imports: [
    CommandModule.register({
      tableName: 'cat',
      dataSyncHandlers: [CatDataSyncRdsHandler],
    }),
  ],
  controllers: [CatController],
  providers: [CatService],
  exports: [CatService],
})
export class CatModule {}

Module Components

Component	Description
imports	List of imported modules that export providers used in this module
controllers	Controllers that handle HTTP requests
providers	Services and other providers available for injection
exports	Providers that should be available in modules that import this module

Framework Modules

MBC CQRS Serverless provides several ready-to-use modules:

Core Modules

Module	Package	Purpose
CommandModule	@mbc-cqrs-serverless/core	CQRS command handling and data sync
SequenceModule	@mbc-cqrs-serverless/sequence	Sequential ID generation
TenantModule	@mbc-cqrs-serverless/tenant	Multi-tenant management

Feature Modules

Module	Package	Purpose
TaskModule	@mbc-cqrs-serverless/task	Async task execution with Step Functions
MasterModule	@mbc-cqrs-serverless/master	Master data and settings management
ImportModule	@mbc-cqrs-serverless/import	CSV/API data import

Support Modules

Module	Package	Purpose
NotificationModule	@mbc-cqrs-serverless/core	Email notifications via SES
UISettingModule	@mbc-cqrs-serverless/core	User interface settings storage

Dynamic Module Registration

Most framework modules are dynamic modules that accept configuration:

CommandModule

CommandModule.register({
  tableName: 'cat',
  dataSyncHandlers: [CatDataSyncRdsHandler],
  skipError: false,
  disableDefaultHandler: false,
})

Option	Type	Default	Description
tableName	string	Required	DynamoDB table name (without postfix)
dataSyncHandlers	Type[]	[]	Data sync handler classes
skipError	boolean	false	Skip errors during data sync
disableDefaultHandler	boolean	false	Disable default data sync to data table

SequenceModule

SequenceModule.register({
  tableName: 'sequences',
})

MasterModule

MasterModule.register({
  enableController: true,
})

Creating Custom Modules

Step 1: Create Module File

// src/order/order.module.ts
import { Module } from '@nestjs/common';
import { CommandModule } from '@mbc-cqrs-serverless/core';
import { SequenceModule } from '@mbc-cqrs-serverless/sequence';

import { OrderController } from './order.controller';
import { OrderService } from './order.service';
import { OrderDataSyncHandler } from './handlers/order-data-sync.handler';

@Module({
  imports: [
    CommandModule.register({
      tableName: 'order',
      dataSyncHandlers: [OrderDataSyncHandler],
    }),
    SequenceModule.register({
      tableName: 'sequences',
    }),
  ],
  controllers: [OrderController],
  providers: [OrderService],
  exports: [OrderService],
})
export class OrderModule {}

Step 2: Register in AppModule

// src/app.module.ts
import { Module } from '@nestjs/common';
import { OrderModule } from './order/order.module';

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

Best Practices

1. One module per entity: Create a dedicated module for each business entity
2. Export services, not controllers: Only export providers that other modules need
3. Use forRoot for global modules: Register global configuration once in AppModule
4. Keep modules focused: Each module should have a single responsibility

Related Documentation

• NestJS Modules: Official NestJS module documentation
• CommandModule: Detailed CommandModule configuration
• Data Sync Handlers: Creating data sync handlers