When you create an Angular library, you can provide and package it with schematics that integrate it with the Angular CLI.
With your schematics, your users can use `ng add` to install an initial version of your library,
`ng generate` to create artifacts defined in your library, and `ng update` to adjust their project for a new version of your library that introduces breaking changes.
All three types of schematics can be part of a collection that you package with your library.
Download the <live-exampledownloadOnly>library schematics project</live-example> for a completed example of the steps below.
## Creating a schematics collection
To start a collection, you need to create the schematic files.
The following steps show you how to add initial support without modifying any project files.
1. In your library's root folder, create a `schematics/` folder.
1. In the `schematics/` folder, create an `ng-add/` folder for your first schematic.
1. At the root level of the `schematics/` folder, create a `collection.json` file.
1. Edit the `collection.json` file to define the initial schema for your collection.
* The `$schema` path is relative to the Angular Devkit collection schema.
* The `schematics` object describes the named schematics that are part of this collection.
* The first entry is for a schematic named `ng-add`. It contains the description, and points to the factory function that is called when your schematic is executed.
1. In your library project's `package.json` file, add a "schematics" entry with the path to your schema file.
The Angular CLI uses this entry to find named schematics in your collection when it runs commands.
The only step needed to provide initial `ng add` support is to trigger an installation task using the `SchematicContext`.
The task uses the user's preferred package manager to add the library to the project's `package.json` configuration file, and install it in the project’s `node_modules` directory.
In this example, the function receives the current `Tree` and returns it without any modifications.
If you need to, you can do additional setup when your package is installed, such as generating files, updating configuration, or any other initial setup your library requires.
## Building your schematics
To bundle your schematics together with your library, you must configure the library to build the schematics separately, then add them to the bundle.
You must build your schematics *after* you build your library, so they are placed in the correct directory.
* Your library needs a custom Typescript configuration file with instructions on how to compile your schematics into your distributed library.
* To add the schematics to the library bundle, add scripts to the library's `package.json` file.
Assume you have a library project `my-lib` in your Angular workspace.
To tell the library how to build the schematics, add a `tsconfig.schematics.json` file next to the generated `tsconfig.lib.json` file that configures the library build.
1. Edit the `tsconfig.schematics.json` file to add the following content.
1. To make sure your schematics source files get compiled into the library bundle, add the following scripts to the `package.json` file in your library project's root folder (`projects/my-lib`).
* The `build` script compiles your schematic using the custom `tsconfig.schematics.json` file.
* The `copy:*` statements copy compiled schematic files into the proper locations in the library output folder in order to preserve the file structure.
* The `postbuild` script copies the schematic files after the `build` script completes.
## Providing generation support
You can add a named schematic to your collection that lets your users use the `ng generate` command to create an artifact that is defined in your library.
We'll assume that your library defines a service, `my-service`, that requires some setup. You want your users to be able to generate it using the following CLI command.
To begin, create a new subfolder, `my-service`, in the `schematics` folder.
### Configure the new schematic
When you add a schematic to the collection, you have to point to it in the collection's schema, and provide configuration files to define options that a user can pass to the command.
1. Edit the `schematics/collection.json` file to point to the new schematic subfolder, and include a pointer to a schema file that will specify inputs for the new schematic.
* *name* : The name you want to provide for the created service.
* *path* : Overrides the path provided to the schematic. The default path value is based on the current working directory.
* *project* : Provides a specific project to run the schematic on. In the schematic, you can provide a default if the option is not provided by the user.
### Add template files
To add artifacts to a project, your schematic needs its own template files.
Schematic templates support special syntax to execute code and variable substitution.
1. Create a `files/` folder inside the `schematics/my-service/` folder.
1. Create a file named `__name@dasherize__.service.ts.template` that defines a template you can use for generating files. This template will generate a service that already has Angular's `HttpClient` injected into its constructor.
* The `name` is provided as a property from your factory function. It is the same `name` you defined in the schema.
### Add the factory function
Now that you have the infrastructure in place, you can define the main function that performs the modifications you need in the user's project.
The Schematics framework provides a file templating system, which supports both path and content templates.
The system operates on placeholders defined inside files or paths that loaded in the input `Tree`.
It fills these in using values passed into the `Rule`.
For details of these data structure and syntax, see the [Schematics README](https://github.com/angular/angular-cli/blob/master/packages/angular_devkit/schematics/README.md).
1. Create the main file, `index.ts` and add the source code for your schematic factory function.
1. First, import the schematics definitions you will need. The Schematics framework offers many utility functions to create and use rules when running a schematic.
This simple rule factory returns the tree without modification.
The options are the option values passed through from the `ng generate` command.
## Define a generation rule
We now have the framework in place for creating the code that actually modifies the user's application to set it up for the service defined in your library.
The Angular workspace where the user has installed your library contains multiple projects (applications and libraries).
The user can specify the project on the command line, or allow it to default.
In either case, your code needs to identify the specific project to which this schematic is being applied, so that you can retrieve information from the project configuration.
You can do this using the `Tree` object that is passed in to the factory function.
The `Tree` methods give you access to the complete file tree in your workspace, allowing you to read and write files during the execution of the schematic.
1. To determine the destination project, use the `Tree.read()` method to read the contents of the workspace configuration file, `angular.json`, at the root of the workspace.
* Be sure to check that the context exists and throw the appropriate error.
* After reading the contents into a string, parse the configuration into a JSON object, typed to the `WorkspaceSchema`.
1. The `WorkspaceSchema` contains all the properties of the workspace configuration, including a `defaultProject` value for determining which project to use if not provided.
We will use that value as a fallback, if no project is explicitly specified in the `ng generate` command.
A `Rule` can use external template files, transform them, and return another `Rule` object with the transformed template. You can use the templating to generate any custom files required for your schematic.
1. Add the following code to your factory function.
* The `apply()` method applies multiple rules to a source and returns the transformed source. It takes 2 arguments, a source and an array of rules.
* The `url()` method reads source files from your filesystem, relative to the schematic.
* The `applyTemplates()` method receives an argument of methods and properties you want make available to the schematic template and the schematic filenames. It returns a `Rule`. This is where you define the `classify()` and `dasherize()` methods, and the `name` property.
* The `classify()` method takes a value and returns the value in title case. For example, if the provided name is `my service`, it is returned as `MyService`
* The `dasherize()` method takes a value and returns the value in dashed and lowercase. For example, if the provided name is MyService, it is returned as `my-service`.
For more information about rules and utility methods, see [Provided Rules](https://github.com/angular/angular-cli/tree/master/packages/angular_devkit/schematics#provided-rules).
## Running your library schematic
After you build your library and schematics, you can install the schematics collection to run against your project. The steps below show you how to generate a service using the schematic you created above.
### Build your library and schematics
From the root of your workspace, run the `ng build` command for your library.
Your library and schematics are packaged and placed in the `dist/my-lib` folder at the root of your workspace. For running the schematic, you need to link the library into your `node_modules` folder. From the root of your workspace, run the `npm link` command with the path to your distributable library.
