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Part-4 | NestJS(v9) | Angular(v14) | MongoDB | CRUD Example

The main objectives of this article are:
  • Create HTTP GET endpoint  in nestjs application
  • Consume GET API and render the response in angular component

Create HTTP Get Endpoint In NestJS Application:

In 'SuperHeroesService' implement logic to fetch the data from the MongoDB
NestJS_App/src/super-heroes/super-heroes.service.ts:
import { Injectable } from '@nestjs/common';
import { InjectModel } from '@nestjs/mongoose';
import { Model } from 'mongoose';
import { SuperHeroes, SuperHeroesDocument } from './schema/super-heroes.schema';

@Injectable()
export class SuperHeroesService {
  constructor(
    @InjectModel(SuperHeroes.name) private superHeroModel: Model<SuperHeroesDocument>,
  ) {}

  async getAll():Promise<SuperHeroes[]>{
    return await this.superHeroModel.find().exec();
  }
}
  • (12-14) The 'find()' method fetches all documents from the MongoDB collection.
Let's create the 'SuperHereosController' in the 'SuperHeroesModule'.
nest g co super-heroes --no-spec

Now let's add the HTTP Get endpoint in our 'SuperHeroesController'.
NestJS_App/src/super-heroes/super-heroes.controller.ts:
import { Controller, Get } from '@nestjs/common';
import { SuperHeroesService } from './super-heroes.service';

@Controller('super-heroes')
export class SuperHeroesController {

    constructor(private superHeroService:SuperHeroesService){}

    @Get()
    async getAll(){
        return await this.superHeroService.getAll();
    }
}
  • (Line: 4) To make our 'SuperHeroesController' class a controller it has to be decorated with '@controller' that loads from the '@nestjs/common'. The '@controller' takes a string as input, that string will be the part of the endpoint.
  • (Line: 7) Inject our 'SuperHeroesService'.
  • (Line: 9) The '@Get()' decorator makes our method to consumed only for the HTTP Get request.
Now run the application and navigate to "http://localhost:3000/super-heroes"

Create An Angular Component Like 'AllSuperHeroes':

Let's create an angular component like 'AllSuperHeroes' inside of the 'super-heroes' folder(new folder).
ng generate component super-heroes/all-super-heroes  --skip-tests

Now configure routing for  'all-super-heroes.component.ts' in 'app-routing.module.ts'
Angular_App/src/app/super-heroes/all-super-heroes/all-super-heroes.component.ts:
import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
import { AllSuperHeroesComponent } from './super-heroes/all-super-heroes/all-super-heroes.component';

const routes: Routes = [
  {
    path: '',
    component: AllSuperHeroesComponent,
  },
];

@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule],
})
export class AppRoutingModule {}
  • (Line: 6-9) The 'AllSuperHeroesComponent' is configured to the home page URL.

Create 'SuperHeroes' Model In Angular Application:

Let's create an API response model like 'SuperHeroes' in our angular application.
ng generate interface super-heroes/super-heroes
Angular_App/src/app/super-heroes/super-heroes.ts:
export interface SuperHeroes {
  _id: string;
  name: string;
  franchise: string;
  powers: string;
  imageUrl: string;
}

Create Service To Invoke API Calls In Angular Application:

Let's create a service file in our angular application in which we will implement all logic for invoking the API call.
ng generate service super-heroes/super-heroes --skip-tests
Angular_App/src/app/super-heroes/super-heroes.service.ts:
import { Injectable } from '@angular/core';
import {HttpClient} from '@angular/common/http'
import { SuperHeroes } from './super-heroes';

@Injectable({
  providedIn: 'root'
})
export class SuperHeroesService {

  constructor(private http:HttpClient) { }

  get(){
    return this.http.get<SuperHeroes[]>("http://localhost:3000/super-heroes")
  }
}
  • (Line: 5-8) To make our 'SuperHeroesService' a service entity it has to be decorated with the '@Injectable' that loads from the '@angular/core'.
  • (Line: 10) Injected the 'HttpClient' instance that loads from the '@angular/common/http'.
  • (Line: 12-14) Here invoking the get API call using the 'HttpClient.get<T>()' method.
Now import  the 'HttpClientModule' into the 'AppModule'.
Angular_App/src/app/app.module.ts:
import { HttpClientModule } from '@angular/common/http';
// existing code hidden for display purpose
@NgModule({
  imports: [
    HttpClientModule
  ]
})
export class AppModule { }

Invoke API And Render The API Response In 'AllSuperHeroes' Angular Component:

Let's implement the logic to call HTTP Get API and then render the API response in the 'AllSuperHeroes' angular component.
Angular_App/src/app/super-heroes/all-super-heroes/all-super-heroes.component.ts:
import { Component, OnInit } from '@angular/core';
import { SuperHeroes } from '../super-heroes';
import { SuperHeroesService } from '../super-heroes.service';

@Component({
  selector: 'app-all-super-heroes',
  templateUrl: './all-super-heroes.component.html',
  styleUrls: ['./all-super-heroes.component.css'],
})
export class AllSuperHeroesComponent implements OnInit {
  constructor(private superHeroService: SuperHeroesService) {}

  superHeroes: SuperHeroes[] = [];

  ngOnInit(): void {
    this.getAll();
  }

  getAll() {
    this.superHeroService.get().subscribe((data) => {
      this.superHeroes = data;
    });
  }
}
  • (Line: 7) The 'templateUrl' property is configured with the path of the HTML file of the component.
  • (Line: 8) The 'styleUrls' property takes an array of CSS files that needed by our component.
  • (Line: 10) To make our 'AllSuperHeroesComponent' an angular component it has to be decorated with the '@Component' decorator. Here our component class implements the 'OnInit' so we have to implement the 'ngOnInit' life cycle method in our component. 
  • (Line: 11) Inject our 'SuperHeroesService'.
  • (Line: 13) Initialized the variable 'superHeroes' in which we are going to store our API response.
  • (Line: 19-22) Invoking the API and response is assigned to the 'superHeroes' variable
  • (Line: 15-17) The 'ngOnInit' is a life cycle method executed on the component invoked. In this method, we are calling our API invoking method.
Angular_App/src/app/super-heroes/all-super-heroes/all-super-heroes.component.html:
<div class="container mt-2">
  <div class="row row-cols-1 row-cols-md-3 g-2">
    <div class="col" *ngFor="let item of superHeroes">
      <div class="card">
        <img src="{{ item.imageUrl }}" class="card-img-top" alt="..." />
        <div class="card-body">
          <h5 class="card-title">{{ item.name }}</h5>
          <p class="card-text"><b>Franchise:</b> {{ item.franchise }}</p>
          <p class="card-text"><b>Powers:</b> {{item.powers}}</p>
        </div>
      </div>
    </div>
  </div>
</div>
  • In angular to render dynamic data into the component HTML file, we use "{{dynamic_component_property}}".
  • In angular to loop any HTML content, we use '*ngFor'
  • (Line: 3) Here looping our bootstrap card to render the collection of data in the 'superHeroes' component variable
Now run both our NestJS(http://localhost:3000) and Angular(http://localhost:4200) applications. We can observe an issue with CORS(cross-origin issue) because the application has different domains or port numbers. So to fix the issue let's enable cors at our NestJS application.
NestJS_App/src/main.ts:
import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.enableCors();
  await app.listen(3000);
}
bootstrap();
  • (Line: 6) The 'app.enableCors()' make our API can be consumed by any client.
Now check our Application, 'CORS' will be no more.
(Step 1)

(Step: 2)

In the next article, we implement the create operation.

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