Angular Schematics

What are Schematics?

Schematics are template-based code generators that support complex logic. They are the engine behind ng generate commands and ng add package installations. Schematics can create, modify, delete, and move files while applying rules and templates to scaffold or modify code.

Think of schematics as “code recipes” - they describe how to generate or transform code in a repeatable, configurable way.

How Schematics Work

Schematics operate on a virtual file system called a tree. Changes are staged in memory before being committed to disk, allowing for validation and rollback.

Tree

Virtual file system representing project structure

Rule

Transformation applied to the tree

Template

File template with placeholders

Action

Create, update, delete, or rename operations

Official Schematics

Angular provides built-in schematics for common tasks:

Code Generation Schematics

ng generate @schematics/angular:component user-profile

Generates:

Component TypeScript file
Component template (HTML)
Component styles (CSS/SCSS)
Component test file

Options:

--standalone: Create standalone component
--inline-template: Use inline template
--inline-style: Use inline styles
--skip-tests: Skip test file
--flat: Don’t create folder
--export: Export from module

ng generate @schematics/angular:service auth

Generates:

Service TypeScript file
Service test file

Options:

--skip-tests: Skip test file
--flat: Don’t create folder

ng generate @schematics/angular:module admin

Generates:

Module TypeScript file
Optional routing module

Options:

--routing: Add routing module
--flat: Don’t create folder
--module: Parent module to import into

ng generate @schematics/angular:directive highlight

Generates:

Directive TypeScript file
Directive test file

Options:

--standalone: Create standalone directive
--skip-tests: Skip test file
--flat: Don’t create folder

ng generate @schematics/angular:pipe currency-format

Generates:

Pipe TypeScript file
Pipe test file

Options:

--standalone: Create standalone pipe
--skip-tests: Skip test file
--flat: Don’t create folder

ng generate @schematics/angular:guard auth

Generates:

Guard TypeScript file (functional by default)
Guard test file

Options:

--functional: Generate functional guard (default)
--skip-tests: Skip test file

Migration Schematics

Angular provides powerful migration schematics:

Standalone Migration

Convert components, directives, and pipes to standalone:

ng generate @angular/core:standalone

Three-phase migration:

Convert to Standalone

Convert declarations to standalone and update imports

Remove NgModules

Delete unnecessary NgModule classes

Update Bootstrap

Switch to bootstrapApplication API

Options:

mode: Migration mode (convert, prune, bootstrap)
path: Relative path to migrate

See the standalone migration README for details.

Control Flow Migration

Migrate to new control flow syntax:

ng generate @angular/core:control-flow-migration

Transforms:

*ngIf → @if
*ngFor → @for
*ngSwitch → @switch

Before:

<div *ngIf="show">Content</div>
<li *ngFor="let item of items">{{ item }}</li>

After:

@if (show) {
  <div>Content</div>
}
@for (item of items; track item) {
  <li>{{ item }}</li>
}

Signal Migrations

Migrate to signal-based APIs:Signal Inputs:

ng generate @angular/core:signal-input-migration

Signal Queries:

ng generate @angular/core:signal-queries-migration

Output Migration:

ng generate @angular/core:output-migration

Style Migrations

NgStyle to Style:

ng generate @angular/core:ngstyle-to-style-migration

NgClass to Class:

ng generate @angular/core:ngclass-to-class-migration

Other Migrations

Inject Migration:

ng generate @angular/core:inject-migration

Router Testing Module:

ng generate @angular/core:router-testing-module-migration

Cleanup Unused Imports:

ng generate @angular/core:cleanup-unused-imports

All migration schematics support a --path option to migrate specific directories.

Creating Custom Schematics

Build your own code generators for common patterns in your application.

Setup

Install Schematics CLI

npm install -g @angular-devkit/schematics-cli

Create Schematics Collection

schematics blank my-schematics
cd my-schematics
npm install

Project Structure

my-schematics/
├── src/
│   ├── my-schematic/
│   │   ├── index.ts           # Schematic logic
│   │   ├── schema.json        # Options schema
│   │   ├── schema.d.ts        # TypeScript interface
│   │   └── files/             # Templates
│   │       └── __name@dasherize__/
│   │           ├── __name@dasherize__.component.ts
│   │           └── __name@dasherize__.component.html
│   └── collection.json        # Collection metadata
├── package.json
└── tsconfig.json

Define Schema

schema.json:

{
  "$schema": "http://json-schema.org/schema",
  "$id": "MySchematic",
  "type": "object",
  "properties": {
    "name": {
      "type": "string",
      "description": "The name of the component",
      "$default": {
        "$source": "argv",
        "index": 0
      }
    },
    "path": {
      "type": "string",
      "format": "path",
      "description": "The path to create the component",
      "visible": false
    },
    "project": {
      "type": "string",
      "description": "The name of the project"
    },
    "export": {
      "type": "boolean",
      "default": false,
      "description": "Export the component from the module"
    }
  },
  "required": ["name"]
}

schema.d.ts:

export interface Schema {
  name: string;
  path?: string;
  project?: string;
  export?: boolean;
}

Implement Schematic

index.ts:

import {
  Rule,
  SchematicContext,
  Tree,
  apply,
  url,
  template,
  mergeWith,
  move,
  chain,
  SchematicsException,
} from '@angular-devkit/schematics';
import { strings, normalize, experimental } from '@angular-devkit/core';
import { Schema } from './schema';

export function mySchematic(options: Schema): Rule {
  return (tree: Tree, context: SchematicContext) => {
    // Validate options
    if (!options.name) {
      throw new SchematicsException('Option "name" is required.');
    }

    // Get workspace
    const workspaceConfig = tree.read('/angular.json');
    if (!workspaceConfig) {
      throw new SchematicsException('Could not find Angular workspace configuration');
    }

    // Parse workspace
    const workspace: experimental.workspace.WorkspaceSchema = JSON.parse(
      workspaceConfig.toString()
    );

    // Determine project
    if (!options.project) {
      options.project = workspace.defaultProject;
    }

    const project = workspace.projects[options.project!];
    if (!project) {
      throw new SchematicsException(`Project "${options.project}" not found.`);
    }

    // Determine path
    if (options.path === undefined) {
      options.path = `${project.sourceRoot}/app`;
    }

    // Apply template
    const templateSource = apply(url('./files'), [
      template({
        ...strings,
        ...options,
      }),
      move(normalize(options.path as string)),
    ]);

    return chain([
      mergeWith(templateSource),
      // Add additional rules here
    ])(tree, context);
  };
}

Create Templates

files/__name@dasherize__/__name@dasherize__.component.ts:

import { Component } from '@angular/core';

@Component({
  selector: 'app-<%= dasherize(name) %>',
  templateUrl: './<%= dasherize(name) %>.component.html',
  styleUrls: ['./<%= dasherize(name) %>.component.<%= style %>'],
  standalone: true
})
export class <%= classify(name) %>Component {
  constructor() { }
}

files/__name@dasherize__/__name@dasherize__.component.html:

<div class="<%= dasherize(name) %>-container">
  <h2><%= classify(name) %> Component</h2>
  <p><%= dasherize(name) %> works!</p>
</div>

Template Functions

Angular provides utility functions for string transformation:

String Functions

Function	Input	Output	Description
`dasherize`	`MyComponent`	`my-component`	Convert to kebab-case
`classify`	`my-component`	`MyComponent`	Convert to PascalCase
`camelize`	`my-component`	`myComponent`	Convert to camelCase
`capitalize`	`hello`	`Hello`	Capitalize first letter
`underscore`	`MyComponent`	`my_component`	Convert to snake_case

Schematic Rules

Rules define transformations applied to the tree:

Basic Rules

import { Rule, Tree } from '@angular-devkit/schematics';

// Create a file
export function createFile(): Rule {
  return (tree: Tree) => {
    tree.create('new-file.ts', 'console.log("Hello");');
    return tree;
  };
}

// Read a file
export function readFile(): Rule {
  return (tree: Tree) => {
    const content = tree.read('existing-file.ts');
    if (content) {
      console.log(content.toString());
    }
    return tree;
  };
}

// Update a file
export function updateFile(): Rule {
  return (tree: Tree) => {
    const recorder = tree.beginUpdate('file.ts');
    recorder.insertLeft(0, '// File header\n');
    tree.commitUpdate(recorder);
    return tree;
  };
}

// Delete a file
export function deleteFile(): Rule {
  return (tree: Tree) => {
    tree.delete('old-file.ts');
    return tree;
  };
}

Chaining Rules

import { chain, Rule } from '@angular-devkit/schematics';

export function mySchematic(): Rule {
  return chain([
    createFile(),
    updateFile(),
    deleteFile(),
  ]);
}

Conditional Rules

import { Rule, SchematicContext } from '@angular-devkit/schematics';

export function conditionalRule(options: Schema): Rule {
  return (tree: Tree, context: SchematicContext) => {
    if (options.export) {
      context.logger.info('Exporting component...');
      // Add export logic
    }
    
    return tree;
  };
}

Advanced Features

Working with AST

Modify TypeScript files using Abstract Syntax Trees:

import * as ts from 'typescript';
import { InsertChange } from '@schematics/angular/utility/change';

function addImport(tree: Tree, filePath: string): Tree {
  const source = tree.read(filePath);
  if (!source) return tree;
  
  const sourceFile = ts.createSourceFile(
    filePath,
    source.toString(),
    ts.ScriptTarget.Latest,
    true
  );
  
  // Find where to insert import
  const allImports = sourceFile.statements.filter(
    node => ts.isImportDeclaration(node)
  );
  
  const lastImport = allImports[allImports.length - 1];
  const insertPos = lastImport ? lastImport.end + 1 : 0;
  
  // Create change
  const change = new InsertChange(
    filePath,
    insertPos,
    "\nimport { Component } from '@angular/core';\n"
  );
  
  // Apply change
  const recorder = tree.beginUpdate(filePath);
  recorder.insertLeft(change.pos, change.toAdd);
  tree.commitUpdate(recorder);
  
  return tree;
}

External Schematics

Call other schematics from your schematic:

import { externalSchematic, Rule, chain } from '@angular-devkit/schematics';

export function mySchematic(options: Schema): Rule {
  return chain([
    // Call Angular's component schematic
    externalSchematic('@schematics/angular', 'component', {
      name: options.name,
      standalone: true,
    }),
    // Add custom logic
    customRule(options),
  ]);
}

Task Scheduling

Schedule tasks to run after schematic completes:

import { Rule, SchematicContext } from '@angular-devkit/schematics';
import { NodePackageInstallTask } from '@angular-devkit/schematics/tasks';

export function mySchematic(): Rule {
  return (tree: Tree, context: SchematicContext) => {
    // Schedule npm install
    context.addTask(new NodePackageInstallTask());
    
    return tree;
  };
}

Testing Schematics

Test schematics using the testing utilities:

import { SchematicTestRunner, UnitTestTree } from '@angular-devkit/schematics/testing';
import * as path from 'path';

describe('my-schematic', () => {
  const collectionPath = path.join(__dirname, '../collection.json');
  const runner = new SchematicTestRunner('schematics', collectionPath);
  
  let appTree: UnitTestTree;
  
  beforeEach(() => {
    appTree = runner.runExternalSchematic(
      '@schematics/angular',
      'workspace',
      { name: 'workspace', version: '14.0.0' }
    );
  });
  
  it('should create component files', async () => {
    const options = { name: 'test' };
    
    const tree = await runner.runSchematic('my-schematic', options, appTree);
    
    expect(tree.files).toContain('/test/test.component.ts');
    expect(tree.files).toContain('/test/test.component.html');
  });
  
  it('should have correct content', async () => {
    const options = { name: 'test' };
    
    const tree = await runner.runSchematic('my-schematic', options, appTree);
    const content = tree.readContent('/test/test.component.ts');
    
    expect(content).toContain('class TestComponent');
    expect(content).toContain('standalone: true');
  });
});

Publishing Schematics

Build the Package

npm run build

Test Locally

npm link
cd /path/to/test-project
npm link my-schematics
ng generate my-schematics:my-schematic test

Publish to npm

npm publish

Use in Projects

ng add my-schematics
ng generate my-schematics:my-schematic test

Collection Configuration

collection.json:

{
  "$schema": "../node_modules/@angular-devkit/schematics/collection-schema.json",
  "schematics": {
    "my-schematic": {
      "description": "Generate a custom component",
      "factory": "./my-schematic/index#mySchematic",
      "schema": "./my-schematic/schema.json",
      "aliases": ["ms"],
      "hidden": false
    },
    "ng-add": {
      "description": "Add my-schematics to the project",
      "factory": "./ng-add/index#ngAdd",
      "schema": "./ng-add/schema.json"
    }
  }
}

factory

string

required

Path to schematic implementation and export name

schema

string

Path to JSON schema file defining options

aliases

string[]

Alternative names for the schematic

hidden

boolean

Hide from ng generate list

Best Practices

Validation

Always validate options and check for existing files:

if (!options.name) {
  throw new SchematicsException('Name is required');
}

if (tree.exists(targetPath)) {
  throw new SchematicsException(`File already exists: ${targetPath}`);
}

Logging

Provide helpful feedback:

context.logger.info('Creating component...');
context.logger.warn('This will overwrite existing files');
context.logger.error('Failed to create component');
context.logger.debug('Debug information');

Dry Run

Test with --dry-run flag:

ng generate my-schematics:my-schematic test --dry-run

Shows what would be generated without creating files.

Path Handling

Use normalize and join for cross-platform compatibility:

import { normalize, join } from '@angular-devkit/core';

const targetPath = normalize(join(options.path, options.name));

Next Steps

CLI Overview

Return to CLI overview

Builders

Learn about custom builders

Resources

Schematics Guide

Official schematics documentation