Services

Let's talk about Dependency injection before we move to services

Dependency injection

Dependency injection is basically providing the objects that an object needs (its dependencies) instead of having it construct them itself. It's a very useful technique for testing, since it allows dependencies to be mocked or stubbed out.

And this take us to services Sections

Services

A service is an instance of a TypeScript/JavaScript class decorated with @Injectable() decorator.

import { Injectable } from "@sustain/core";
import { User } from "../models/user.model.ts";

@Injectable()
export class UserService {
    private users = [ ... ] // bunch of fata
    constructor() { }

    getById(id: string): User {
        return this.users.find((user: any) => user._id === id);
    }
    allUsers(): User[] {
        return this.users;
    }
}

📄 app.ts

The service can be imported in the main application or in one of the application modules, that can be injected using the Injector whenever we need it.

...
@App({
    modules: [
        UserModule
    ],
    controllers: [
        HelloController,
        BaseController
    ],
    providers: [
       UserService, // <---- imported here
    ]
})
class AppModule { }
...

Then our UserService can be Injected in any application controllers

Let's create our controller UserController

import { UserService } from './UserService';
import { Controller } from '@sustain/core';
import { Get, Response, Param } from '@sustain/common';

@Controller('/user')
export default class UserController {
    constructor(
        private userService: UserService // <-- Injected here
    ) { }

    @Get()
    allUsers(): any[] {
        return this.userService.list();
    }

    @Get('/:id')
    singleUser(
        @Response() response: any,
        @Param('id') id: string,
    ): any {
        response.setHeader('Content-Type', 'application/json');
        return this.userService.get(id);
    }
}

Passing the UserService in the constructor the Injector will grap an Instance of the service and it will be accessible in the controller.

← ControllersInterceptors →