How to make a sequence of http requests in Angular 6 using RxJS

Question

With the help of code snippet can you tell me How to make a sequence of http requests in Angular 6 using RxJS

Answer 1

You can utilize the concatMap operator. This operator ensures that each observable is processed sequentially, maintaining the order of execution.

Implementation Steps:

Import Necessary Modules:

import { HttpClient } from '@angular/common/http';

import { Injectable } from '@angular/core';

import { Observable } from 'rxjs';

import { concatMap } from 'rxjs/operators';

Define the Service Methods:

@Injectable({

  providedIn: 'root',

})

export class ApiService {

  constructor(private http: HttpClient) {}

  firstPOSTCall(data: any): Observable<any> {

    return this.http.post('https://api.example.com/first', data);

  }

  secondPOSTCall(data: any): Observable<any> {

    return this.http.post('https://api.example.com/second', data);

  }

  // Add more methods as needed

}

Chain the HTTP Requests Using concatMap:

import { Component } from '@angular/core';

import { ApiService } from './api.service';

@Component({

  selector: 'app-sequential-requests',

  template: `<p>Check the console for output</p>`,

})

export class SequentialRequestsComponent {

  constructor(private apiService: ApiService) {

    this.executeSequentialRequests();

  }

  executeSequentialRequests() {

    const initialData = { /* initial data */ };

    this.apiService.firstPOSTCall(initialData)

      .pipe(

        concatMap(result1 => this.apiService.secondPOSTCall(result1)),

        // Add more concatMap operators for additional sequential calls

      )

      .subscribe(

        finalResult => {

          console.log('Final result:', finalResult);

          // Handle the final result

        },

        error => {

          console.error('An error occurred:', error);

          // Handle errors appropriately

        }

      );

  }

}