Handling Observable in Angular using Async Pipe

Async pipe in angular helps in transforming data received asynchronously and when used along with an observable allows to:

• Subscribe to the observable
• Get its latest values
• Marks it for onPush change detection
• Automatically unsubscribes on destruction of the component

#angular 8 #angular app #angular route #angular services #observables

What is GEEK

Buddha Community

Handling Observable in Angular using Async Pipe

Async pipe in angular helps in transforming data received asynchronously and when used along with an observable allows to:

• Subscribe to the observable
• Get its latest values
• Marks it for onPush change detection
• Automatically unsubscribes on destruction of the component

#angular 8 #angular app #angular route #angular services #observables

Angular Observables: How to Use Observables In Angular

Angular Observables provide the support for passing the messages between publishers(Creator of Observables) and subscribers(User of Observables) in your application. Observables are declarative that is, you define the function for publishing values, but it is not executed until the consumer subscribes to it. We have already covered the  Angular 9 Tutorial on this blog.

The observable can deliver the multiple values of any type like literals, messages, or events, depending on the context. As a publisher, you can create an Observable instance that defines a subscriber function. This is a function that is executed when the consumer calls the subscribe() method.

Define Angular Observers

The handler for receiving the observable notifications implements the Observer interface. It is an object that defines the callback methods to handle the three types of notifications that an observable can send. These are the following.

1. next: Required. The handler for each delivered value called zero or more times after execution starts.
2. error: Optional. The handler for error notification. The error halts the execution of the observable instance.
3. complete: Optional. The handler for an execution-complete notification. The delayed values can continue to be delivered to a next handler after execution is complete.

#angular #angular observables #angular 9

Install Angular - Angular Environment Setup Process

Angular is a TypeScript based framework that works in synchronization with HTML, CSS, and JavaScript. To work with angular, domain knowledge of these 3 is required.

1. Installing Node.js and npm
2. Installing Angular CLI
3. Creating workspace
4. Deploying your First App

In this article, you will get to know about the Angular Environment setup process. After reading this article, you will be able to install, setup, create, and launch your own application in Angular. So let’s start!!!

Install Angular in Easy Steps

For Installing Angular on your Machine, there are 2 prerequisites:

• Node.js
• npm Package Manager

Node.js

First you need to have Node.js installed as Angular require current, active LTS or maintenance LTS version of Node.js

Download and Install Node.js version suitable for your machine’s operating system.

Npm Package Manager

Angular, Angular CLI and Angular applications are dependent on npm packages. By installing Node.js, you have automatically installed the npm Package manager which will be the base for installing angular in your system. To check the presence of npm client and Angular version check of npm client, run this command:

1. npm -v

Installing Angular CLI

• Open Terminal/Command Prompt
• To install Angular CLI, run the below command:

1. npm install -g @angular/cli

· After executing the command, Angular CLI will get installed within some time. You can check it using the following command

1. ng --version

Workspace Creation

Now as your Angular CLI is installed, you need to create a workspace to work upon your application. Methods for it are:

• Using CLI
• Using Visual Studio Code

1. Using CLI

To create a workspace:

• Navigate to the desired directory where you want to create your workspace using cd command in the Terminal/Command prompt
• Then in the directory write this command on your terminal and provide the name of the app which you want to create. In my case I have mentioned DataFlair:

1. Ng new YourAppName

• After running this command, it will prompt you to select from various options about the CSS and other functionalities.

• To leave everything to default, simply press the Enter or the Return key.

#angular tutorials #angular cli install #angular environment setup #angular version check #download angular #install angular #install angular cli

Angular Rxjs: Use .map() And Async Pipe (Refactor Your Code)

In this video, we will see how to improve our code using the #rxs map operator and #angular #async pipe.

The components should be clean and minimal and should not have code that manipulates the data. Responsible for data manipulation is a service.
The goal is to prepare our data and return an #observable pipe so that we can use an #async pipe in the template.

code: https://github.com/profanis/codeShotsWithProfanis/tree/13/rxjsMapAndAsyncPipe

#angular #rxjs #observable #map #async

#angular rxjs #angular #angular tutorial #what is angular

How to Use Async Pipe in Angular 8 application

In this article, we are going to learn how to use Async pipe in Angular applications.

What is Async Pipe?

Async Pipe is an impure pipe which automatically subscribes to an observable to emit the latest values. It not only subscribes to an observable but also it subscribes to promise and calls the then method .When the components get destroyed it automatically unsubscribes it to reduce memory leaks.

Advantages of Async Pipe

1. Async Pipe makes rendering of data from observable and promise easier.
2. For promises it automatically calls then method and
3. For observables it automatically calls subscribe and unsubscribe.

Prerequisites

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

Step 1

Let’s create a new Angular project using the following NPM command,

ng new asyncPipe

Step 2

Now, let’s create a new component by using the following command,

ng g c async-pipe-example

Step 3

Now, open the async-pipe-example.component.html file and add the following code in the file,

<div class="card">    
  <div class="card-body pb-0">    
    <h4 style="text-align: center;">{{SampleMessage}}</h4>    
    <div class="row">    
      <div class="col-12 col-md-12">    
        <div class="card">    
    
          <div class="card-body position-relative">    
            <div class="table-responsive cnstr-record product-tbl">    
              <table class="table table-bordered heading-hvr">    
                <thead>    
                  <tr>    
                     
                    <th width="50">Art.No    
                    </th>    
                    <th>Brand</th>    
                    <th>    
                      Price/Unit</th>    
                    <th>Provider</th>    
                    <th>P. Art. N</th>    
                    <th>S. A/C</th>    
               
                  </tr>    
                </thead>    
    
                <tbody *ngFor="let product of products$ | async">    
                  <tr>    
                    <td align="center">{{product.ArtNo}}</td>    
                    <td>{{product.Brand}}</td>    
                    <td>{{product.Price }}</td>    
                    <td>{{product.Provider}}</td>    
                    <td>{{product.ProviderArtNo}}</td>    
                    <td>{{product.SalesAccount}}</td>    
                 
                  </tr>    
                </tbody>    
              </table>    
            </div>    
          </div>    
        </div>    
      </div>    
    </div>    
  </div>    
</div>  

Here in the below code we can see how to apply async pipe with our structural direcrtive *ngFor

<tbody *ngFor="let product of products$ | async"> 

Step 4

Now, open the async-pipe-example.component.ts file and add the following code in this file,

import { Component, OnInit } from '@angular/core';    
import { ProductsService } from '../product.service';    
import { Observable } from 'rxjs';    
    
@Component({    
  selector: 'app-async-pipe-example',    
  templateUrl: './async-pipe-example.component.html',    
  styleUrls: ['./async-pipe-example.component.css']    
})    
export class AsyncPipeExampleComponent implements OnInit {    
  products = [];    
  products$:Observable<any>;    
  SampleMessage="Example of Angular Async Pipe";    
    
  constructor(private _productService:ProductsService) { }    
    
  ngOnInit() {    
    //this.getProductsUsingSubscribeMethod();    
    this.getProductsUsingAsyncPipe();    
  }    
    
  public getProductsUsingSubscribeMethod() {    
    this.SampleMessage="Example of Angular Subscribe Method";    
    this._productService.getAllProducts().subscribe((data: any) => {    
      this.products =data;    
      console.log(data);    
    })    
  }    
    
  public getProductsUsingAsyncPipe() {    
    this.SampleMessage="Example of Angular Async Pipe";    
    this.products$ =this._productService.getAllProducts();    
  }    
    
}   

Here in the below code we are using observables of any type and to get the asynchronous flow data either we can use subscribe method to subscribe the observables or we can simply use ‘async pipe’ which automatically subscribes to an Observable and returns the latest value and it also unsubscribes automatically to avoid memory leaks.

public getProductsUsingAsyncPipe() {      
  this.SampleMessage="Example of Angular Async Pipe";      
  this.products$ =this._productService.getAllProducts();      
}   

Step 5

Now, open the product.service.ts file and add the following code,

import { Injectable } from '@angular/core';    
import { HttpClient } from '@angular/common/http';    
  
@Injectable()       
export class ProductsService {      
    private url = '';    
    private baseUrl = "http://localhost:49661/";//Replace it with your http address and port      
    constructor(public http: HttpClient) {    
    }      
    getAllProducts() {    
        this.url = this.baseUrl+'api/Product/getAllProducts';    
        return this.http.get<any[]>(this.url);    
    }      
}   

WEB API - Create an ASP.NET application

Follow these steps to create an ASP.NET application.

Step 1

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

Step 2

Choose the Create option and select Asp.net web application.

Step 3

Select Web API and click Ok.

Step 4

Now right click on controller and then add a new item.

Step 5

Choose Ado.net Entity Data Model and then click on Add.

Step 6

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 new connection

Step 8

Copy your database connection server name and paste it in the server name textbox. You will see all the database, select your database and click on ok.

Step 9

The next popup will show, paste your database server name, and choose for the database and test for the connection then click on next. 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 as “Product controller” and add the following namespace in the student controller.

Here is the complete code for getting all the product data and their nested product information data.

Complete Product controller code

using System.Linq;  
using System.Web.Http;  
using CompanyDetails.Models;  
namespace CompanyDetails.Controllers {  
    [RoutePrefix("api/Company")]  
    public class CompanyController: ApiController {  
        CompanyEntities2 DB = new CompanyEntities2();  
        [HttpGet]  
        [Route("getAllProducts")]  
        public object getAllProducts(string countrycode) {  
            var productDetails = DB.USP_GetAllProducts().ToList();  
            return productDetails;  
        }  
    }  
}  

Now, it’s time to enable CORS. Go to Tools, open NuGet Package Manager, search for CORS, and install the “Microsoft.Asp.Net.WebApi.Cors” package.

If you are running your frontend application in a different port and your server is running in another port, then to avoid a Cross-Origin-Resource-Sharing issue you have to add small code in webapiconfig.cs file.

Open Webapiconfig.cs and add the following lines.

EnableCorsAttribute cors = new EnableCorsAttribute("*", "*", "*");  
config.EnableCors(cors);  

BACKEND

Here we will do back end related code  using SQL server

The very first step is to create a database.

Create database

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

Step 1

Create a database product

create database product  

Step 2

Create a product table using the following code,

USE [Product]  
GO  
/****** Object: Table [dbo].[Product] Script Date: 12/18/2019 10:23:19 PM ******/  
SET ANSI_NULLS ON  
GO  
SET QUOTED_IDENTIFIER ON  
GO  
CREATE TABLE [dbo].[Product](  
[ProductId] [int] IDENTITY(1,1) NOT NULL,  
[ArtNo] [nvarchar](50) NULL,  
[Provider] [nvarchar](50) NULL,  
[ProviderArtNo] [nvarchar](50) NULL,  
[Brand] [nvarchar](50) NULL,  
CONSTRAINT [PK_Product] PRIMARY KEY CLUSTERED  
(  
[ProductId] ASC  
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]  
) ON [PRIMARY]  
GO  

Make product ID the primary key

Now it’s time to add some store procedures.

Step 4

All you have to do is paste the following code in a new query,

USE [Product]  
GO  
/****** Object: StoredProcedure [dbo].[USP_GetAllProducts] Script Date: 12/18/2019 10:24:35 PM ******/  
SET ANSI_NULLS ON  
GO  
SET QUOTED_IDENTIFIER ON  
GO  
ALTER Proc [dbo].[USP_GetAllProducts]  
As  
Begin  
Select p.*,pci.Price,pci.BuyAccount,pci.SalesAccount from [Product] p  
End  

With this step we have successfully completed our front end, web API, and back end coding.

Now it’s time to run the project by using ‘npm start’ or ‘ng serve’ command and check the output.

Conclusion

In this article, we have learned how to use async pipe in Angular 8 Application.

Please give your valuable feedback/comments/questions about this article. Please let me know if you liked and understood this article and how I could improve it.

Thank you!

#angular #tutorial #async pipe in Angular #programming