Difference Between Observable and Promise With Example in Angular 8

Observables Vs Promise

Observables and Promise both provide us with abstractions that help us deal with the asynchronous nature of applications.

Promise

Promise work with asynchronous operations. They either return a single value (i.e, the promise resolves) or an error message (i.e, the promise rejects)

Another important thing to remember regarding promises is that a request initiated from a promise is not cancellable.

Disadvantages of Promise

1. The user could not cancel a request to the API
2. A user could not retry a failed call
3. As our application gets bigger, Promise becomes hard to manage

Observables

An Observable is an Array or a sequence of events over time. It has at least two participants. The creator (the data source) and the subscriber (the subscription where data is being consumed). Compared to a promise, an observable can be canceled.

RxJS is all about unifying the ideas of promise callbacks and data flow and making them easier to work with.

Observables provide operators like map.forEach, reduce, similar to an array.

There are also powerful operators like retry().or reply(),retryWhen(),delay()

Prerequisites

• Basic knowledge of Angular
• Visual Studio Code must be installed
• Angular CLI must be installed
• Node JS must be installed

Back End

Here, with Backend related code, we will do it using the SQL server.

The very first step is to create a database.

Step 1. Let’s create a database on your local SQL Server. I hope you have installed SQL Server 2017 on your machine (you can use SQL Server 2008, 2012, or 2016, as well).

CREATE DATABASE country;

Step 2. Create a Country Table using the following code.

CREATE TABLE tbl_Countries
(
    CountryID INT,
    CountryName VARCHAR(50),
    TwoCharCountryCode CHAR(2),
    ThreeCharCountryCode CHAR(3)
);

INSERT INTO tbl_Countries VALUES
(1,'Afghanistan','AF','AFG'),
(2,'Aland Islands','AX','ALA'),
(3,'Albania','AL','ALB'),
(4,'Algeria','DZ','DZA'),
(5,'American Samoa','AS','ASM'),
(6,'Andorra','AD','AND'),
(7,'Angola','AO','AGO'),
(8,'Anguilla','AI','AIA'),
(9,'Antarctica','AQ','ATA'),
(10,'Antigua and Barbuda','AG','ATG'),
(11,'Argentina','AR','ARG'),
(12,'Armenia','AM','ARM'),
(13,'Aruba','AW','ABW'),
(14,'Australia','AU','AUS'),
(15,'Austria','AT','AUT'),
(16,'Azerbaijan','AZ','AZE'),
(17,'Bahamas','BS','BHS'),
(18,'Bahrain','BH','BHR'),
(19,'Bangladesh','BD','BGD'),
(20,'Barbados','BB','BRB'),
(21,'Belarus','BY','BLR'),
(22,'Belgium','BE','BEL'),
(23,'Belize','BZ','BLZ'),
(24,'Benin','BJ','BEN'),
(25,'Bermuda','BM','BMU'),
(26,'Bhutan','BT','BTN'),
(27,'Bolivia','BO','BOL'),
(28,'Bonaire, Sint Eustatius and Saba','BQ','BES'),
(29,'Bosnia and Herzegovina','BA','BIH'),
(30,'Botswana','BW','BWA'),
(31,'Bouvet Island','BV','BVT'),
(32,'Brazil','BR','BRA'),
(33,'British Indian Ocean Territory','IO','IOT'),
(34,'Brunei','BN','BRN'),
(35,'Bulgaria','BG','BGR'),
(36,'Burkina Faso','BF','BFA'),
(37,'Burundi','BI','BDI'),
(38,'Cambodia','KH','KHM'),
(39,'Cameroon','CM','CMR'),
(40,'Canada','CA','CAN'),
(41,'Cape Verde','CV','CPV'),
(42,'Cayman Islands','KY','CYM'),
(43,'Central African Republic','CF','CAF'),
(44,'Chad','TD','TCD'),
(45,'Chile','CL','CHL'),
(46,'China','CN','CHN'),
(47,'Christmas Island','CX','CXR'),
(48,'Cocos (Keeling) Islands','CC','CCK'),
(49,'Colombia','CO','COL'),
(50,'Comoros','KM','COM'),
(51,'Congo','CG','COG'),
(52,'Cook Islands','CK','COK'),
(53,'Costa Rica','CR','CRI'),
(54,'Ivory Coast','CI','CIV'),
(55,'Croatia','HR','HRV'),
(56,'Cuba','CU','CUB'),
(57,'Curacao','CW','CUW'),
(58,'Cyprus','CY','CYP'),
(59,'Czech Republic','CZ','CZE'),
(60,'Democratic Republic of the Congo','CD','COD'),
(61,'Denmark','DK','DNK'),
(62,'Djibouti','DJ','DJI'),
(63,'Dominica','DM','DMA'),
(64,'Dominican Republic','DO','DOM'),
(65,'Ecuador','EC','ECU'),
(66,'Egypt','EG','EGY'),
(67,'El Salvador','SV','SLV'),
(68,'Equatorial Guinea','GQ','GNQ'),
(69,'Eritrea','ER','ERI'),
(70,'Estonia','EE','EST'),
(71,'Ethiopia','ET','ETH'),
(72,'Falkland Islands (Malvinas)','FK','FLK'),
(73,'Faroe Islands','FO','FRO'),
(74,'Fiji','FJ','FJI'),
(75,'Finland','FI','FIN'),
(76,'France','FR','FRA'),
(77,'French Guiana','GF','GUF'),
(78,'French Polynesia','PF','PYF'),
(79,'French Southern Territories','TF','ATF'),
(80,'Gabon','GA','GAB'),
(81,'Gambia','GM','GMB'),
(82,'Georgia','GE','GEO'),
(83,'Germany','DE','DEU'),
(84,'Ghana','GH','GHA'),
(85,'Gibraltar','GI','GIB'),
(86,'Greece','GR','GRC'),
(87,'Greenland','GL','GRL'),
(88,'Grenada','GD','GRD'),
(89,'Guadaloupe','GP','GLP'),
(90,'Guam','GU','GUM'),
(91,'Guatemala','GT','GTM'),
(92,'Guernsey','GG','GGY'),
(93,'Guinea','GN','GIN'),
(94,'Guinea-Bissau','GW','GNB'),
(95,'Guyana','GY','GUY'),
(96,'Haiti','HT','HTI'),
(97,'Heard Island and McDonald Islands','HM','HMD'),
(98,'Honduras','HN','HND'),
(99,'Hong Kong','HK','HKG'),
(100,'Hungary','HU','HUN'),
(101,'Iceland','IS','ISL'),
(102,'India','IN','IND'),
(103,'Indonesia','ID','IDN'),
(104,'Iran','IR','IRN'),
(105,'Iraq','IQ','IRQ'),
(106,'Ireland','IE','IRL'),
(107,'Isle of Man','IM','IMN'),
(108,'Israel','IL','ISR'),
(109,'Italy','IT','ITA'),
(110,'Jamaica','JM','JAM'),
(111,'Japan','JP','JPN'),
(112,'Jersey','JE','JEY'),
(113,'Jordan','JO','JOR'),
(114,'Kazakhstan','KZ','KAZ'),
(115,'Kenya','KE','KEN'),
(116,'Kiribati','KI','KIR'),
(117,'Kosovo','XK','---'),
(118,'Kuwait','KW','KWT'),
(119,'Kyrgyzstan','KG','KGZ'),
(120,'Laos','LA','LAO'),
(121,'Latvia','LV','LVA'),
(122,'Lebanon','LB','LBN'),
(123,'Lesotho','LS','LSO'),
(124,'Liberia','LR','LBR'),
(125,'Libya','LY','LBY'),
(126,'Liechtenstein','LI','LIE'),
(127,'Lithuania','LT','LTU'),
(128,'Luxembourg','LU','LUX'),
(129,'Macao','MO','MAC'),
(130,'Macedonia','MK','MKD'),
(131,'Madagascar','MG','MDG'),
(132,'Malawi','MW','MWI'),
(133,'Malaysia','MY','MYS'),
(134,'Maldives','MV','MDV'),
(135,'Mali','ML','MLI'),
(136,'Malta','MT','MLT'),
(137,'Marshall Islands','MH','MHL'),
(138,'Martinique','MQ','MTQ'),
(139,'Mauritania','MR','MRT'),
(140,'Mauritius','MU','MUS'),
(141,'Mayotte','YT','MYT'),
(142,'Mexico','MX','MEX'),
(143,'Micronesia','FM','FSM'),
(144,'Moldava','MD','MDA'),
(145,'Monaco','MC','MCO'),
(146,'Mongolia','MN','MNG'),
(147,'Montenegro','ME','MNE'),
(148,'Montserrat','MS','MSR'),
(149,'Morocco','MA','MAR'),
(150,'Mozambique','MZ','MOZ'),
(151,'Myanmar (Burma)','MM','MMR'),
(152,'Namibia','NA','NAM'),
(153,'Nauru','NR','NRU'),
(154,'Nepal','NP','NPL'),
(155,'Netherlands','NL','NLD'),
(156,'New Caledonia','NC','NCL'),
(157,'New Zealand','NZ','NZL'),
(158,'Nicaragua','NI','NIC'),
(159,'Niger','NE','NER'),
(160,'Nigeria','NG','NGA'),
(161,'Niue','NU','NIU'),
(162,'Norfolk Island','NF','NFK'),
(163,'North Korea','KP','PRK'),
(164,'Northern Mariana Islands','MP','MNP'),
(165,'Norway','NO','NOR'),
(166,'Oman','OM','OMN'),
(167,'Pakistan','PK','PAK'),
(168,'Palau','PW','PLW'),
(169,'Palestine','PS','PSE'),
(170,'Panama','PA','PAN'),
(171,'Papua New Guinea','PG','PNG'),
(172,'Paraguay','PY','PRY'),
(173,'Peru','PE','PER'),
(174,'Phillipines','PH','PHL'),
(175,'Pitcairn','PN','PCN'),
(176,'Poland','PL','POL'),
(177,'Portugal','PT','PRT'),
(178,'Puerto Rico','PR','PRI'),
(179,'Qatar','QA','QAT'),
(180,'Reunion','RE','REU'),
(181,'Romania','RO','ROU'),
(182,'Russia','RU','RUS'),
(183,'Rwanda','RW','RWA'),
(184,'Saint Barthelemy','BL','BLM'),
(185,'Saint Helena','SH','SHN'),
(186,'Saint Kitts and Nevis','KN','KNA'),
(187,'Saint Lucia','LC','LCA'),
(188,'Saint Martin','MF','MAF'),
(189,'Saint Pierre and Miquelon','PM','SPM'),
(190,'Saint Vincent and the Grenadines','VC','VCT'),
(191,'Samoa','WS','WSM'),
(192,'San Marino','SM','SMR'),
(193,'Sao Tome and Principe','ST','STP'),
(194,'Saudi Arabia','SA','SAU'),
(195,'Senegal','SN','SEN'),
(196,'Serbia','RS','SRB'),
(197,'Seychelles','SC','SYC'),
(198,'Sierra Leone','SL','SLE'),
(199,'Singapore','SG','SGP'),
(200,'Sint Maarten','SX','SXM'),
(201,'Slovakia','SK','SVK'),
(202,'Slovenia','SI','SVN'),
(203,'Solomon Islands','SB','SLB'),
(204,'Somalia','SO','SOM'),
(205,'South Africa','ZA','ZAF'),
(206,'South Georgia and the South Sandwich Islands','GS','SGS'),
(207,'South Korea','KR','KOR'),
(208,'South Sudan','SS','SSD'),
(209,'Spain','ES','ESP'),
(210,'Sri Lanka','LK','LKA'),
(211,'Sudan','SD','SDN'),
(212,'Suriname','SR','SUR'),
(213,'Svalbard and Jan Mayen','SJ','SJM'),
(214,'Swaziland','SZ','SWZ'),
(215,'Sweden','SE','SWE'),
(216,'Switzerland','CH','CHE'),
(217,'Syria','SY','SYR'),
(218,'Taiwan','TW','TWN'),
(219,'Tajikistan','TJ','TJK'),
(220,'Tanzania','TZ','TZA'),
(221,'Thailand','TH','THA'),
(222,'Timor-Leste (East Timor)','TL','TLS'),
(223,'Togo','TG','TGO'),
(224,'Tokelau','TK','TKL'),
(225,'Tonga','TO','TON'),
(226,'Trinidad and Tobago','TT','TTO'),
(227,'Tunisia','TN','TUN'),
(228,'Turkey','TR','TUR'),
(229,'Turkmenistan','TM','TKM'),
(230,'Turks and Caicos Islands','TC','TCA'),
(231,'Tuvalu','TV','TUV'),
(232,'Uganda','UG','UGA'),
(233,'Ukraine','UA','UKR'),
(234,'United Arab Emirates','AE','ARE'),
(235,'United Kingdom','GB','GBR'),
(236,'United States','US','USA'),
(237,'United States Minor Outlying Islands','UM','UMI'),
(238,'Uruguay','UY','URY'),
(239,'Uzbekistan','UZ','UZB'),
(240,'Vanuatu','VU','VUT'),
(241,'Vatican City','VA','VAT'),
(242,'Venezuela','VE','VEN'),
(243,'Vietnam','VN','VNM'),
(244,'Virgin Islands, British','VG','VGB'),
(245,'Virgin Islands, US','VI','VIR'),
(246,'Wallis and Futuna','WF','WLF'),
(247,'Western Sahara','EH','ESH'),
(248,'Yemen','YE','YEM'),
(249,'Zambia','ZM','ZMB'),
(250,'Zimbabwe','ZW','ZWE');

Now, let's add Store Procedures.

Step 3. Create a Stored Procedure of the following,

CREATE PROC searchCountryByName
@VALUE nvarchar(50)
AS
BEGIN
    SELECT * FROM [dbo].[tbl_Countries] WHERE CountryName LIKE '' + @VALUE + '%'
END

Web API
 

Create an ASP.NET Core application

Follow these steps to create an ASP.NET Core application.

Step 1. In Visual Studio 2019, click on File -> New -> Project.

Step 2. Choose the Create option and select the ASP.NET web application.

Step 3. Select Web API and click OK.

Step 4. Now right-click on the controller and add a new item.

Step 5. Choose Ado.net Entity Data Model, then click on Add.

Step 6. The next step is EF Designer; just click on next.

Step 7. A new pop-up will show. Click on next. If yours isn't established, then click on a new connection.

Step 8. Copy your database connection server name and paste it into the server name textbox. You will see all the databases, select your database, and click on OK.

Step 9. Here, in the new screen, select your tables and store the procedure. Then click on finish.

Our next step is to right-click on the Controllers folder and add a new controller. Name it "CountryController" and add the following namespace in the Countrycontroller.

Complete Countrycontroller code

using System.Linq;
using System.Web.Http;
using CompanyDetails.Entities;

namespace CountryDetails.Controllers
{
    [RoutePrefix("api/Country")]
    public class CountryController : ApiController
    {
        CountryEntities5 DB = new CountryEntities5();

        [HttpGet]
        [Route("getSearchedCountry")]
        public object getSearchedCountry(string keyword)
        {
            var countryResult = DB.searchCountryByName(keyword).ToList();
            return countryResult;
        }
    }
}

Front End

Step 1. Let's create a new Angular project using the following NPM command.

ng new observablevspromise

Step 2. Now, let's create a new component for "Observable " by using the following command.

ng g c observable-example

Step 3. Now, let's create a new component for "Promise" by using the following command.

ng g c promise-example

Here, I am creating two different components, one for observable examples and another for promise.

First, we will see the example of Promise.

Step 4. Now, open the promise-example.component.html file and add the following code to the file.

<div style="text-align: center;">
  <h1>
    Example of Fetching data using Promise
  </h1>
  <div>
    <h2>
      Country Name Search
    </h2>
    <input #term type="text" (keyup)="searchCountryUsingPromise(term.value)">
    <div>
      <li *ngFor="let result of country">
        {{result.CountryName}}
      </li>
    </div>
  </div>
</div>

Step 5. Now, open the promise-example.component.ts file and add the following code to this file.

import { Component, OnInit } from '@angular/core';
import { CountryService } from '../country.service';

@Component({
  selector: 'app-promise-example',
  templateUrl: './promise-example.component.html',
  styleUrls: ['./promise-example.component.css']
})
export class PromiseExampleComponent implements OnInit {
  country: any;

  constructor(private _countryService: CountryService) { }

  ngOnInit() {
  }

  public searchCountryUsingPromise(keyWord) {
    this._countryService.getSearchedCountry(keyWord).toPromise()
      .then((data: any) => {
        console.log(data);
        this.country = data;
      });
  }
}

Step 6. The next step is to create a service.

ng g s country.service.ts

Now, open the country.service.ts file and add the following code to this file.

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

@Injectable()
export class CountryService {
  employees: any[];

  private url = '';
  private baseUrl = "http://localhost:49661/"; // Replace it with your http address and port

  constructor(public http: HttpClient) {
  }

  getSearchedCountry(keyWord) {
    this.url = this.baseUrl + 'api/Country/getSearchedCountry?keyword=' + keyWord;
    return this.http.get<any[]>(this.url);
  }
}

Step 7. Open the file app.module.ts and paste the below code.

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { AppComponent } from './app.component';
import { HttpClientModule } from '@angular/common/http';
import { TrackbyComponent } from './trackby/trackby.component';
import { ObservableExampleComponent } from './observable-example/observable-example.component';
import { PromiseExampleComponent } from './promise-example/promise-example.component';
import { CountryService } from './country.service';

@NgModule({
  declarations: [
    AppComponent,
    TrackbyComponent,
    ObservableExampleComponent,
    PromiseExampleComponent
  ],
  imports: [
    BrowserModule,
    FormsModule,
    ReactiveFormsModule,
    HttpClientModule
  ],
  providers: [CountryService],
  bootstrap: [AppComponent]
})
export class AppModule { }

Step 8. Now, open app.component.html and add the below code.

<app-promise-example></app-promise-example>

Now it is time for the Output.

As we can see, whenever I am typing the key, it hits the API every time (i.e., it goes to the server and gets the data).

Example of Observable

Step 9. Now, open the observable-example.component.html file and add the following code to the file.

<div style="text-align: center;">
  <h1>
    Example of Fetching data using Observable
  </h1>
  <div>
    <h2>
      Country Name Search
    </h2>
    <input type="text" [formControl]="term">
    <div>
      <li *ngFor="let result of country">
        {{result.CountryName}}
      </li>
    </div>
  </div>
</div>

Step 10. Now, open the observable-example.component.ts file and add the following code to this file

import { Component, OnInit } from '@angular/core';
import { CountryService } from '../country.service';
import { FormControl } from '@angular/forms';
import 'rxjs/add/operator/debounceTime';
import 'rxjs/add/operator/distinctUntilChanged';

@Component({
  selector: 'app-observable-example',
  templateUrl: './observable-example.component.html',
  styleUrls: ['./observable-example.component.css']
})
export class ObservableExampleComponent implements OnInit {
  country: any;

  constructor(private _countryService: CountryService) { }

  private term = new FormControl();

  ngOnInit() {
    this.term.valueChanges
      .debounceTime(400)
      .distinctUntilChanged()
      .subscribe(searchText => {
        this._countryService.getSearchedCountry(searchText).subscribe((result) => {
          console.log(result);
          this.country = result;
        });
      });
  }
}

Step 11. Replace the app.component.html file with the below code.

<app-observable-example></app-observable-example>

Now it is time for the output to be observable.

As we can see, as soon as I press the key, it hits the API every 400 milliseconds, so rather than hitting it on every keypress, it hits every 400 milliseconds using the debounce time operator in RxJS.

So with the help of RxJS operators, we can achieve this so that it can improve our application performance.

Conclusion

In this article, we have seen the difference between Observable and Promise in Angular 8 Applications.

Please give your valuable feedback/comments/questions about this article. Please let me know how to improve it.

In my next article, we are going to learn the RxJS operators with examples.