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# Code Generation
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Generate NestJS components, services, controllers, and other architectural elements using Angular DevKit schematics. The CLI provides built-in support for the @nestjs/schematics collection with comprehensive code generation capabilities.
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## Capabilities
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### Generate Command
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Creates NestJS elements using schematics with extensive customization options.
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```bash { .api }
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# Generate elements
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nest generate <schematic> [name] [path] [options]
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nest g <schematic> [name] [path] [options]
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# Options:
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-d, --dry-run                       # Report actions without writing results
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-p, --project [project]             # Project in which to generate files
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--flat                             # Enforce flat structure of generated element
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--no-flat                          # Enforce that directories are generated
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--spec                             # Enforce spec files generation (default: true)
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--spec-file-suffix [suffix]        # Use custom suffix for spec files
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--skip-import                      # Skip importing (default: false)
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--no-spec                          # Disable spec files generation
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-c, --collection [collectionName]  # Schematics collection to use
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```
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**Usage Examples:**
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```bash
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# Generate a controller
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nest generate controller users
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nest g controller users
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# Generate in specific path
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nest g controller users --path=modules/users
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# Generate without spec files
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nest g controller users --no-spec
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# Generate with flat structure
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nest g service users --flat
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# Generate in specific project (monorepo)
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nest g controller users --project=api
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# Dry run to preview changes
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nest g controller users --dry-run
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# Generate with custom collection
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nest g controller users --collection=@my/schematics
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```
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## Available Schematics
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The @nestjs/schematics collection provides the following generators:
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### Core Elements
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```bash { .api }
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# Application
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nest g application <name>          # Generate a new application (for monorepos)
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nest g app <name>                  # Alias for application
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# Library  
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nest g library <name>              # Generate a new library (for monorepos)
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nest g lib <name>                  # Alias for library
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```
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### Controllers and Services
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```bash { .api }
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# Controller
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nest g controller <name>           # Generate a controller class
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nest g co <name>                   # Alias for controller
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# Service
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nest g service <name>              # Generate a service class  
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nest g s <name>                    # Alias for service
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# Provider
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nest g provider <name>             # Generate a provider class
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nest g pr <name>                   # Alias for provider
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```
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### Modules and Structure
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```bash { .api }
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# Module
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nest g module <name>               # Generate a module class
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nest g mo <name>                   # Alias for module
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# Resource (full CRUD)
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nest g resource <name>             # Generate complete CRUD resource
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nest g res <name>                  # Alias for resource
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```
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### Advanced Elements
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```bash { .api }
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# Middleware
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nest g middleware <name>           # Generate middleware class
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nest g mi <name>                   # Alias for middleware
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# Guard
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nest g guard <name>                # Generate guard class
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nest g gu <name>                   # Alias for guard
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# Interceptor  
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nest g interceptor <name>          # Generate interceptor class
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nest g in <name>                   # Alias for interceptor
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# Decorator
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nest g decorator <name>            # Generate decorator function
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nest g d <name>                    # Alias for decorator
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# Pipe
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nest g pipe <name>                 # Generate pipe class
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nest g pi <name>                   # Alias for pipe
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# Filter
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nest g filter <name>               # Generate exception filter class
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nest g f <name>                    # Alias for filter
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```
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### Gateways and Resolvers
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```bash { .api }
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# Gateway (WebSockets)
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nest g gateway <name>              # Generate WebSocket gateway
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nest g ga <name>                   # Alias for gateway  
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# Resolver (GraphQL)
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nest g resolver <name>             # Generate GraphQL resolver
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nest g r <name>                    # Alias for resolver
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```
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### Configuration Files
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```bash { .api }
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# Class
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nest g class <name>                # Generate a basic class
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nest g cl <name>                   # Alias for class
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# Interface
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nest g interface <name>            # Generate an interface
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nest g interface <name>            # No alias available
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```
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## File Generation Patterns
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### Spec Files
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By default, the CLI generates test specification files alongside components:
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```bash
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# Generates both controller and spec file:
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nest g controller users
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# Creates:
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# - users.controller.ts
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# - users.controller.spec.ts
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```
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### Import Handling
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The CLI automatically handles imports and module registration:
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```bash
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# When generating a controller, it:
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# 1. Creates the controller file
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# 2. Updates the parent module to import the controller
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# 3. Adds the controller to the module's controllers array
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```
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### Directory Structure
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```bash { .api }
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# Flat structure (--flat)
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src/
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├── users.controller.ts
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└── users.controller.spec.ts
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# Nested structure (default)  
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src/
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└── users/
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    ├── users.controller.ts
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    └── users.controller.spec.ts
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```
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## Project Structure Options
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### Monorepo Support
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For monorepo projects, specify the target project:
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```bash { .api }
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# Generate in specific app/library
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nest g controller users --project=api-gateway
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nest g service users --project=shared-lib
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```
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### Path Specification
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Control exactly where files are generated:
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```bash { .api }
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# Generate in custom path
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nest g controller users --path=src/modules/authentication
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nest g service email --path=src/common/services
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```
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## Advanced Options
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### Custom File Suffixes
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Customize the suffix used for spec files:
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```bash { .api }
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# Use custom spec file suffix
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nest g controller users --spec-file-suffix=test
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# Creates: users.controller.test.ts instead of users.controller.spec.ts
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```
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### Skip Import Registration
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Prevent automatic module registration:
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```bash { .api }
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# Generate without adding to module
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nest g controller users --skip-import
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```
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## Resource Generation
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The resource schematic generates a complete CRUD setup:
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```bash { .api }
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# Generate complete resource
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nest g resource users
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# Creates:
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# - users.controller.ts
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# - users.controller.spec.ts  
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# - users.service.ts
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# - users.service.spec.ts
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# - users.module.ts
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# - dto/create-user.dto.ts
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# - dto/update-user.dto.ts
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# - entities/user.entity.ts
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```
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## Error Handling
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The CLI validates schematic names and provides helpful error messages:
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```bash
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# Invalid schematic name
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nest g invalid-schematic users
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# Lists available schematics in a formatted table
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```