Angular 4: Exploring the Depths of Nested HTTP Requests

I'm struggling to receive a JSON response that contains an array with every declaration, including the user and category information. I currently have a static solution, but I want to implement a dynamic approach and I'm facing difficulties making it work.

EDIT: I have hardcoded the 'id' in the method, which limits me to fetching only one declaration. My goal is to create a loop that retrieves all the declarations from http://localhost:8080/declaraties. I attempted nested HTTP requests but without success.

Code:

data.service.ts

    import { Injectable } from '@angular/core';
    import {Http} from '@angular/http';
    import {Observable} from 'rxjs/Observable';
    import 'rxjs/add/observable/forkJoin';
    import 'rxjs/add/observable/of';
    import 'rxjs/add/operator/map';
    import 'rxjs/add/operator/mergeMap';

@Injectable()
export class DataService {

  constructor(private http: Http) { }

  url = 'http://localhost:8080/declaraties/';

  getAllesVanDeclaraties(id: number): Observable<any> {
    return Observable.forkJoin([
      this.http.get('http://localhost:8080/declaraties/' + id).map(res => res.json()),
      this.http.get('http://localhost:8080/declaraties/' + id + '/gebruiker').map(res => res.json()),
      this.http.get('http://localhost:8080/declaraties/' + id + '/categorie').map(res => res.json())
    ])
      .map((data: any[]) => {
          const declaraties: any = data[0];
          const gebruiker: any[] = data[1];
          const categorie: any[] = data[2];
          declaraties.gebruiker = gebruiker;
          declaraties.categorie = categorie;
          return declaraties;
      });
  }
}

row.component.html

<ng-container *ngFor="let decl of data; let i = index;">

    <tr data-toggle="collapse" data-target="#demo1" class="accordion-toggle">
      <th>{{i + 1}}</th>

      <td>{{decl['gebruiker'].naam}}</td>
      <td>{{decl.datumIngediend}}</td>
      <td>{{decl.omschrijving}}</td>
      <td>{{decl['categorie'].naam}}</td>
      <td>&euro; {{decl.bedrag}}</td>

    </tr>......

row.component.ts

import {Component, OnInit} from '@angular/core';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/mergeMap';
import {DataService} from './data.service';

@Component({
  selector: 'app-row',
  templateUrl: './row.component.html',
  styleUrls: ['./app.component.css']
})

export class RowComponent implements OnInit {

  data: any = [];

  constructor(private dataService: DataService) {
  }

  ngOnInit() {
    this.dataService.getAllesVanDeclaraties(2).subscribe( data => {
      console.log(data);
      this.data.push(data);
    });
  }
}

I attempted to use nested HTTP requests, but I'm not receiving any responses.

Answer №1

Give this a shot:

Try the following code snippet:
Observable.forkJoin([
    this.http.get('http://localhost:8080/declaraties/' + id),
    this.http.get('http://localhost:8080/declaraties/' + id + '/gebruiker'),
    this.http.get('http://localhost:8080/declaraties/' + id + '/categorie')
])
.subscribe((data: any) => {
    console.log('data[0]', data[0].json())
    console.log('data[1]', data[1].json())
    console.log('data[2]', data[2].json())
})

Answer №2

The initial step would involve retrieving all declarations using the following method:

this.http.get('http://localhost:8080/declaraties/').map(res =>{ 
  const declarations: any[] = res.json();
  for(let i = 0; i < declarations.length; i++){
    this.http.get('http://localhost:8080/declarations/' + declarations[i].id + '/user')
             .map(user =>{ declarations[i].user = user.json(); })      
    this.http.get('http://localhost:8080/declarations/' + declarations[i].id + '/category')
             .map(category=>{ declarations[i].category = category.json(); })
  }
  return declarations;
})

Answer №3

To streamline the process, consider creating a wrapper method that can efficiently handle an array of ids. This method will leverage your existing getAllesVanDeclaraties function to construct http requests for each id.

// Updated data.service.ts
getAllesArray(ids: number[]){
    // Generate an array of observables
    let declarations = ids.map(id => this.getAllesVanDeclaraties(id));

    // Execute observables concurrently
    return Observable.forkJoin(...declarations);
}

When you subscribe to this method within your component, you will receive data for multiple ids simultaneously.

// Updated component.ts
this.getAllesArray([1, 2]).subscribe(res => {
    // res[0] corresponds to the outcome for id = 1
    // res[1] corresponds to the outcome for id = 2
});

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