plugin-development.md

Plugin Development

Since the Plugin Module is written with NestJS technology, the plugin should also be developed using NestJS.

Plugin Requirements

While creating the plugin we need to provide the necessary parameters. Example plugin settings that we must provide in plugin's package.json as follows:

{
 ...
 "pluginModule": {
  "name": "hello-world-overrider",
  "displayName": "Hello World Overrider"
 },
 ...
}

Variable Name	Description
name	The name field represents the folder name of the plugin.
displayName	This key is the human readable name of the plugin.

The project you write a plugin for needs to be added to the plugin as a package. Plugin development is based on dependency injection feature of NestJS.

{
 ...
 "peerDependencies": {
  "example-service": "^1.0.0"
 }
 ...
}

Creating Plugins

Note

When developing a plugin, the index.ts file added to the root directory is read to instantiate the added class. Within this plugin, you can leave multiple functionalities by adding multiple classes or performing multiple operations associated with the same class.

The manipulation of the getHello and getHelloWord methods within the PluginExampleService defined in PluginExampleModule is exemplified.

import { Module } from '@nestjs/common';
import { PluginExampleService } from './plugin-example.service';

@Module({
  providers: [
    { provide: 'PluginExampleService', useClass: PluginExampleService },
  ],
  exports: ['PluginExampleService'],
})
export class PluginExampleModule {}

import { Injectable } from '@nestjs/common';

@Injectable({})
export class PluginExampleService {
  private textsToAppend: string[];
  constructor() {
    this.textsToAppend = [];
  }
  getHello(): string {
    return this.getHelloWorld() + this.textsToAppend.join(' ');
  }

  getHelloWorld(): string {
    return 'Hello World!';
  }

  appendText(text: string): void {
    this.textsToAppend.push(text);
  }
}

Examples

Overriding A Method

You can override a function and manipulate its intended operation, assigning its return value as desired.

import { Inject, Injectable } from '@nestjs/common';

import { BasePlugin } from 'nestjs-pugin-module';
import { PluginExampleService } from 'example-service';
import { pluginModule } from '../package.json';

@Injectable()
export class HelloWorldOverriderPlugin extends BasePlugin {
  @Inject('PluginExampleService')
  private pluginExampleService: PluginExampleService;
  constructor() {
    super(pluginModule);
  }

  private getHelloWorld(): string {
    return 'Hello World overriden!';
  }

  async load(): Promise<void> {
    this.pluginExampleService.getHelloWorld = this.getHelloWorld;
    return Promise.resolve();
  }
}

Calling A Method

It is possible to call any method in the service which is manipulating. In the example below, data transfer to the variable textsToAppend is facilitated using the appendText method. The transferred data is then added to the return value within the getHello method.

import { Inject, Injectable } from '@nestjs/common';

import { BasePlugin } from 'nestjs-pugin-module';
import { PluginExampleService } from 'example-service';
import { pluginModule } from '../package.json';

@Injectable()
export class HelloWorldOverriderPlugin extends BasePlugin {
  @Inject('PluginExampleService')
  private pluginExampleService: PluginExampleService;
  constructor() {
    super(pluginModule);
  }

  async load(): Promise<void> {
    this.pluginTestService.appendText('Text Example');
    return Promise.resolve();
  }
}

You can explore the Authentication Service for comprehensive examples. The Token Service has been customized by writing a plugin. By examining the Hasura Plugin, you can see how the Token Service is manipulated.