NestJS Module Structure

# NestJS Module Structure
=====================================

## Core Principles
-------------------

*   A NestJS module should be a self-contained unit of functionality.
*   Each module should have a single responsibility and a well-defined interface.
*   Modules should be loosely coupled and highly cohesive.

## Code Style Guidelines
-----------------------

### Naming Conventions

*   Module names should be in PascalCase (e.g., `UsersModule`).
*   Module file names should be in kebab-case (e.g., `users.module.ts`).
*   Module class names should be in PascalCase (e.g., `UsersModule`).
*   Module variables and functions should be in camelCase (e.g., `userService`).

### Typing

*   Use the `@Module` decorator to define a NestJS module.
*   Use the `imports` array to import other modules.
*   Use the `controllers` array to define controllers.
*   Use the `providers` array to define providers (services, repositories, etc.).
*   Use the `exports` array to export providers.

## Best Practices
------------------

### Module Organization

*   Keep each module in its own directory.
*   Use a consistent directory structure across modules (e.g., `modules/users`, `modules/products`).
*   Keep module files (e.g., `users.module.ts`, `users.controller.ts`) in the same directory.

### Module Dependencies

*   Use the `imports` array to import other modules.
*   Avoid circular dependencies between modules.
*   Use lazy loading to load modules only when needed.

### Module Configuration

*   Use the `forRoot` and `forFeature` methods to configure modules.
*   Use environment variables to configure module settings.

## Common Pitfalls to Avoid
---------------------------

### Overly Complex Modules

*   Avoid large, complex modules that are difficult to maintain.
*   Break down complex modules into smaller, more focused modules.

### Tight Coupling

*   Avoid tightly coupling modules together.
*   Use interfaces and dependency injection to decouple modules.

### Duplicate Code

*   Avoid duplicating code across modules.
*   Extract common functionality into shared modules or utilities.

### Incorrect Module Loading

*   Avoid loading modules unnecessarily.
*   Use lazy loading to load modules only when needed.

Example of a well-structured NestJS module:
```typescript
// users.module.ts
import { Module } from '@nestjs/common';
import { UsersController } from './users.controller';
import { UsersService } from './users.service';
import { TypeOrmModule } from '@nestjs/typeorm';
import { UserEntity } from './user.entity';

@Module({
  imports: [TypeOrmModule.forFeature([UserEntity])],
  controllers: [UsersController],
  providers: [UsersService],
  exports: [UsersService],
})
export class UsersModule {}
```