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Angular2 in ASP.NET MVC & Web API

Introduction

Since Angular2 is widely used client framework for web and mobile development, in this article I will try to explain the step by step guide to create basic CRUD (create, read, update and delete) application using Angular2 and MVC Web API as backend RESTful APIs. I will create blank ASP.NET MVC application, setup the Angular2 environment and then create the web application that will have two pages, one for home page that will have only one image and second will be User Management page where data will be loaded from SQL Server Database and user would have options to Add new user, Update and Delete existing user. For all database operation, Anguar2 will call RESTful APIs that we will be developing using ASP.NET MVC Web API.

This is a beginner level article and aimed to be written for novice developers and student who have basic knowledge of programming and want to start learning Angular2, C# and RESTful APIs from scratch. If you are experienced developer and only need an overview, you can just download the attached project and go through it. You need Visual Studio and SQL Server Management Studio to develop the project along the article and compile the attached project. Download the Visual Studio 2017 Community and SQL Server Management Studio.

Let's Start

Setup Angular2 Environment

1. Open Visual Studio, I am using Visual Studio 2017 Community, you can use Visual Studio 2015 Community with Update 3 installed for Node.js and TypeScript packages. (read more about Visual Studio 2015 update 3)
2. Go to File menu and select File -> New -> Project:

3. Enter the Project Name and select your desired .Net Framework (I am using .Net Framework 4.6 for this article). Click on OK button:

4. Select MVC from next screen and check Web API in Add folders and core reference options since we will create RESTful APIs for CRUD operations. Click on OK button:

5. The basic ASP.NET MVC project is created, the next step is to prepare it for Angular2 application. Let's do it next steps.
6. Right click on Project Angular2MVC and select Add -> New Item:

7. Enter package.json in top right search textbox, npm Configuration File would be filtered. Click on Add button to add package.json in project:

8. We will use NPM (Node Package Manager) configuration file to manage all Angular2 packages. To read more about NPM, check this link.
9. Next, copy the Package.json from Angular2 Quick Start GitHub link and paste it in newly added package.json file in Angular2MVC project: 

10. In dependencies section of package.json file, we can see all Angular2 related packages, check here to see what is difference between ^ and ~ sign.
11. Right click on package.json file and select option Restore Packages, Visual Studio Node.js tool will download all dependent packages mentioned in package.json file, in future if you need any additional package, just add it in DevDepnedencies section and restore it, it really makes the life easier: 

12. You would find new folder node_modules added in project that have all the downloaded packages:

13. The next step to let our project know how to get these packages, we will add systemjs.config.js file. Right click on Angular2MVC project and select Add -> JavaScript file:

14. Enter the name systemjs.config.js in Item name field and click on OK button:

15. Copy the systemjs.config.js file's content from Angular2 Quick Start GitHub and paste it in newly added systemjs.config.js file in Angular2MVC project:

16. Next let’s add the TypeScript JSON Configuration File by right clicking on Angular2MVC project and Add -> New Item. Select TypeScript JSON Configuration File and click on OK button:

17. Copy the tsconfig.js file's content from Angular2 Quick Start GitHub and replace it with newly added tsconfig.js file in Angular2MVC project:

18. In case you are getting compilation error while trying to build, don’t worry. As soon we will start adding any typescript file, these errors will go away.
19. Now that our Angular2 setup in ASP.NET MVC is almost completed, it’s time to develop the User Management application but first we need database with one table where we will save the user information.

create User Database & Entity Framework Model

18. Right click on App_Data folder and select Add -> New item. In Data section, you can find the SQL Server Database option. Select it and specify the name as UserDB.

21. Once database is created, double click on UserDB.mdf database file to open the Tables:

22. Right click on UserDB.mdf and select New Query. Paste the following SQL query to create the TblUsertable, click on Execute button to create the table:

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CREATE TABLE [dbo].[TblUser] (
  [Id]     INT       IDENTITY (1, 1) NOT NULL,
  [FirstName] NVARCHAR (250) NULL,
  [LastName]  NVARCHAR (250) NULL,
  [Gender]   NVARCHAR (250) NULL,
  PRIMARY KEY CLUSTERED ([Id] ASC)
);

23. Right click on Tables folder and select option Refresh: 

24. Next lets develop the ASP.NET MVC side that includes setting up Layout and Index pages to load Angular2 main page along MVC controller to load index view and Web API 2.0 controllers for RESTful CRUD (Create, Read, Update and Delete) User APIs.
25. Let’s first go to App_Start folder and configure the route to accept any URL since we can define our custom routing in Angular2 (will do it in upcoming steps). Double click on RouteConfig.cs file to edit it and change the URL in default route as following: 
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    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Web;
    using System.Web.Mvc;
    using System.Web.Routing;
    
    namespace Angular2MVC
    {
        public class RouteConfig
        {
            public static void RegisterRoutes(RouteCollection routes)
            {
                routes.IgnoreRoute("{resource}.axd/{*pathInfo}")
               routes.MapRoute(
                                name: "Default",
                                url: "{*anything}",
                                defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
                            );
            }
        }
    }

    

26. Next let’s open our _Layout.cshtml, clean it up a little bit and add important JavaScripts files to run the Angular2 application. open Views -> Shared -> _Layout.cshtml file. Remove the pre-added top menu and pages link. Add following JS files and system.import statement in header section:

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<script src="/node_modules/core-js/client/shim.min.js"></script>
  <script src="/node_modules/zone.js/dist/zone.js"></script>
  <script src="/node_modules/systemjs/dist/system.src.js"></script>
  <script src="/systemjs.config.js"></script>
  <script>
   System.import('app').catch(function(err){ console.error(err); });
  </script>

Just a brief intro what are these JS files.

Zone.js: A Zone is an execution context that persists across async tasks. For more info click here.

   System.src.js & system.import(‘app’): Configurable module loader enabling dynamic ES module   workflows in browsers and NodeJS. For more info click here.

27. Your final _Layout.cshtml should look like following: 

28. Next let’s create the ADO.NET Entity Data Modal for UserDB database. Right Click on Angular2MVCproject and select Add -> New Folder, specify the name DBContext or anything you want to:

29. Right click on newly created folder DBContext and select Add -> New Item:

30. From left Panel under Visual C#, select Data. On the right side select ADO.NET Entity Data Model. Enter the name UserDBEntities or any of your choice. Click on Add button.

31. From next screen, select EF Designer for Data, click on Next button:

32. Click on New Connection button on the next screen:

33. On next screen, if Data Source is not selected as Microsoft SQL Server Database file (SqlClient), click on Change button and select it: 

34. In Database file name, click on Browse button: 

35. Browse to UserDB databas created in earlier steps and saved in App_Data folder, click on OK button on both Select SQL Server Database File and Connection Properties windows: 

36. Check the Save Connection Settings in Web.Config as checkbox and click on Next button:

37. In next screen, you can select the Entity Framework version, I am using 6.x, you can use according to your choice:

38. On next screen click on Tables checkbox, you would see the only one table TblUser, click on Finishbutton to end the wizard:

39. It will take few seconds and finally you would see our database entity model having one table:

40. Still at this point, if you would try to compile your project, you may get lot of typescript errors, in order to solve it, create the folder with the name app, right click on it and select Add -> TypeScript File:

41. Enter the name main.ts and click OK (we will use this file in upcoming steps). Now rebuild the project, it should be successfully build.

Develop User Management RESTful APIs

41. Next step is to create the ASP.NET MVC Web APIs for read, add, update and delete the user.
42. First we will create the Parent API controller that will have common methods that all API controllers would share, for now we will have only one method to serialize the class object into JSON string for Angular2 front end and also for UserDB database DBContext object to perform database operation in child controller. Right click on Controllers folder and select Add -> Controller…:

44. Select the Web API 2 Controller – Empty and click on Add button:

45. Enter the name BaseAPIController and click on Add button:

46. Add following code in BaseAPIController:

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protected readonly UserDBEntities UserDB = new UserDBEntities();
    protected HttpResponseMessage ToJson(dynamic obj)
    {
      var response = Request.CreateResponse(HttpStatusCode.OK);
      response.Content = new StringContent(JsonConvert.SerializeObject(obj), Encoding.UTF8, "application/json");
      return response;
    }

47. Above given code is quite self-explanatory, we are creating UserDBEntities class object named as UserDB through which we can call methods to Load, Add, Update and Delete users. ToJson method is taking any kind of class object, creating the HTTP Response object with OK HttpStatusCode and serializing the object to JSON string by calling the JsonConvert method from Newtonsoft.jsonlibrary. Final code should looks like following:

48. Next let’s create the RESTful Web APIs for User management i.e. load all users from database, add new user, update and delete existing user. We are creating following methods:
    1. GET method to read all users.
    2. POST method to create new user.
    3. PUT method to update the existing user.
    4. DELETE method to delete existing user.
49. To read more about HTTP Verbs and methods, click here
50. Right click on Controllers folder and select Add -> Controller…

51. Select Web API 2 Controller – Empty and click on Add button:

52. Enter the name UserAPIController and click on Add button:

53. Replace the UserAPIController class code with the following:

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public class UserAPIController : BaseAPIController
    {
        public HttpResponseMessage Get()
        {
            return ToJson(UserDB.TblUsers.AsEnumerable());
        }

       public HttpResponseMessage Post([FromBody]TblUser value)
        {
            UserDB.TblUsers.Add(value);             
            return ToJson(UserDB.SaveChanges());
        }

        public HttpResponseMessage Put(int id, [FromBody]TblUser value)
        {
            UserDB.Entry(value).State = EntityState.Modified;
            return ToJson(UserDB.SaveChanges());
        }
        public HttpResponseMessage Delete(int id)
        {
            UserDB.TblUsers.Remove(UserDB.TblUsers.FirstOrDefault(x => x.Id == id));
            return ToJson(UserDB.SaveChanges());
        }
    }

53. 1. UserAPIController is inherited from BaseAPIController to use UserDB object and ToJsonmethod to convert User entity into JSON string and saving it in HTTP Response Message.
    2. Get(): Load all users from database and return the HTTP Response Message containing Users entity converted to JSON string.
    3. Post([FromBody]TblUser value): Take the User information from front end and save it to database. Return 1 for successfully saved.
    4. Put(int id, [FromBody]TblUser value): Take the existing user id and updated information and update it to database. Return 1 for successfully updated.
    5. Delete(int id): Take existing user id, load the user by id and delete it. Return 1 for successfully deleted.
54. Final UserAPIController class should look like following:

Develop Angular2 Application

55. Now let’s start the exciting part to write the Angular2 code. Before actually writing the code, it is very important to understand the Angular2 architecture, since I am not focusing on writing about Angular2 because you can find plenty of tutorials and free videos about it, let us revise the basic structure of Angular2 if you are lazy enough to go to angular.io website from here:
    1. Modules: Every Angular app has at least one Angular module class, the root module. The application is launched by bootstrapping its root module. During development, you're likely to bootstrap the AppModule in a main.ts file that we will create in next steps. Root module is conventionally named AppModule. In AppModule we specify all components, services or custom pipe filters used by application.
    2. Components: Component controls the view on screen, you can define properties and methodsto control the views. If you ever worked with ASP.NET forms, I would say components are like code behind files aspx.cs file where you interact the aspx file through methods and properties.
    3. Templates: You define a component's view with its companion template. A template is a form of HTML that tells Angular how to render the component. It is like a aspx file in ASP.NET form according to my previous step’s example.
    4. Metadata: Metadata tells Angular how to process a class. If you would see the component, it is just a class, MetaData tells what is template (code behind or you can HTML) associated with this component, any style sheet or how would use this component specified through Selector property.
    5. Data binding: In simple words, how information or control travels between template and component e.g. when you would click any button in template, how would you get click event in component and perform your logic. Angular2 provides following types of data bindings:
       1. {{}} interpolation displays any variable value declared in component.
       2. [ ] property binding is used to send value from parent component to child component. We will use it in our future chapters.
       3. ( ) event binding is used to get any event from template to component. E.g. (click).
    6. Directives: Two kinds of directives exist: structural and attribute directives.
       1. Structural directives alter layout by adding, removing, and replacing elements in DOM. E.g. *ngFor and *ngIf are used to loop through html element and show/hide the element.
       2. Attribute directives alter the appearance or behavior of an existing element. In templates, they look like regular HTML attributes, hence the name. e.g. ngStyle for style sheet, ngModel for two-way data binding.
    7. Services: Service is a broad category encompassing any value, function, or feature that your application needs. There is nothing specifically Angular2 about services. Angular2 has no definition of a service. There is no service base class, and no place to register a service. Services example are Error, Log, HTTP etc. Component should only play the facilitator role between template and user. It should delegate rest of functionality e.g. fetching data from server, deleting or updating, logging, showing error etc. to service.
    8. Dependency injection: Dependency injection is a way to supply a new instance of a class with the fully-formed dependencies it requires. Most dependencies are services. Angular2 uses dependency injection to provide new components with the services they need. E.g. for HTTP service we will use dependency injection to provide the service instance to component in upcoming steps.
    9. For more detail and better understanding, please click here.
56. Hopefully you have got the basic idea about Angular2 architecture, let create user management page (Add, Update, Delete and View users) using Angular 2 in ASP.NET MVC using RESTFul APIs as backend services.
57. In our project, we will create all Angular2 related code in app folder as following convention, if you didn’t create app folder yet, go ahead and create one. If you followed previous steps, you should have one typescript file main.ts in app folder that we will use to bootstrap the AppModule:

58. Before moving further let me show how our final application would look like, it will have two page, one is home page with only large image and second will have table like view with user information, edit and delete button next to each record with one Add button on top of table to Add new user. Each button will open modal pop up where you can perform corresponding functionality, following are the screen shots for both pages and each functionality:

59. Now you have basic idea about our final application let’s start developing the Angular2 piece of application, Let’s keep the Angular2 architecture in mind and create the basic architecture of application.
60. First lets’ create the Angular2 Module that would be the entry point of application. Right click on appfolder and select Add -> TypeScript File:

60. If you don’t see the TypeScript File in second menu, right click on app folder, select Add -> New Item, Search the TypeScrript and select TypeScript file, enter the name and select OK button:

61. Enter the name of new TypeScript File as app.module.ts and click on OK button:

62. Add following code in newly added app.module.ts:

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import { NgModule } from '@angular/core';
import { APP_BASE_HREF } from '@angular/common';
import { BrowserModule } from '@angular/platform-browser';
import { ReactiveFormsModule } from '@angular/forms';
import { HttpModule } from '@angular/http';
 
 @NgModule({
    imports: [BrowserModule, ReactiveFormsModule, HttpModule],
    declarations: [],
    providers: [{ provide: APP_BASE_HREF, useValue: '/' }],
    bootstrap: []
})

export class AppModule { }

63. Just to refresh your memory we are using TypeScipt with Angular2. If you want to learn more about TypeScript, click here.
64. If you quickly go through AppModule class, you can see we are importing required libraries e.g. NgModule from angular core, similarly we will use Reactive forms for user, we are importing ReactiveFormModule from angular Forms package. We will keep extending app.module.ts file by adding user components, service, modal pop up etc.
    1. In NgModule meta data section:
       1. Imports contains modules list.
       2. Declarations contains list of components, we will add user components in next steps.
       3. Providers contains the list of services. We will add service with HTTP operations to perform user read, add, update and delete operations. Right now, it has base href path.
       4. Bootstrap contains the entry component, we will create app.component.ts file in next steps and will add it here.
65. The next step is to edit the main.ts in app folder and add following code in it:

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import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';

import { AppModule } from './app.module';



platformBrowserDynamic().bootstrapModule(AppModule);

66. main.ts code is quite self-explanatory. AppModule reference is imported from current folder, making it as entry Module and loading other helper resources (Bootstrapping) for application by using plateformBrowserDynamic module’s bootstrapModule function. Bootstrap function initialize the Angular2 application, loads the required components, services or other helping resources to run the application. Try to build the project to avoid any error in next steps.
67. Next, create two TypeScripts file app.component.ts and app.routing.ts for main application component and routing table. We will come back to them later, right click on app folder and select Add -> TypeScript File:

68. Enter the name app.component.ts and click on OK button:

69. Again click on app folder and select Add -> TypeScript File, enter the name app.routing.ts and click on OK button:
70. 
71. Next Let’s create the Home component with only one large picture:
72. We will create all user components in new folder, right click on app folder and select Add -> New Folder, enter the name Components:
73. 
74. Right click on newly created folder Component and select Add -> TypeScript File:
75. Enter the name home.component.ts and click on OK button:

74. Add following code in newly created home.component.ts file:

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

@Component({
template: `<img src="../../images/users.png" style="text-align:center"/>`
})

export class HomeComponent{
}

75. In HomeComponent, you can see in MetaData’s template property, we have plain HTML image element from root images folder that will show users.png on screen. You can get any picture, save it in images folder and load it in HomeComponent.
76. Right click on Angular2MVC project and select Add -> New Folder, enter the folder name as images:

76. Right click on newly added folder images and select Open Folder in File Explorer, copy the given below image in opened location:
77. 
78. Our HomeComponent is done, lets view it on screen. We need to do few more steps to do that. The first thing we will do is to create the Routing Table. If you worked with ASP.NET MVC, this routing table is same as MVC Routing table. We will define custom routes for different view components. In second step, we will create our main application component where we will create the navigation menu and load all view components.
    1. Double click on app.routing.ts in app folder to edit it and add following code:

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import { ModuleWithProviders } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';
import { HomeComponent } from './components/home.component';

const appRoutes: Routes = [    
{ path: '', redirectTo: 'home', pathMatch: 'full' },
{ path: 'home', component: HomeComponent }
];

export const routing: ModuleWithProviders = RouterModule.forRoot(appRoutes);

77. In above code we are importing the routing libraries from angular router package and recently created HomeComponent from components folder. In app Routers, the path property is actual URL visible in browser address bar e.g. http://localhost:4500/home. Once we will create the UserComponent, we will add another route for it.
78. Next double click on app.component.ts in app folder to edit it and add following code:

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import { Component } from "@angular/core"
@Component({
     selector: "user-app",
     template: `
               <div>
                  <nav class='navbar navbar-inverse'>
                       <div class='container-fluid'>
                         <ul class='nav navbar-nav'>
                           <li><a [routerLink]="['home']">Home</a></li>
                      </ul>
                      </div>
                 </nav>    
              <div class='container'>
                <router-outlet></router-outlet>
              </div>
             </div>          
`
})

export class AppComponent {
 
}

77. AppComponent is slim one having template with known bootstrap code to create navigation bar with one home link only. The routerlink home name for Home page is what we defined in app.routing.ts’s routing table. You can have defined whatever is convenient for you e.g. default, index etc. router-outletacts as place holder for dynamically loaded view components. We also defined selector property (user-app) in AppComponent MetaData section because we will bootstrap AppComponent in AppModule and use this selector in MVC view (index.cshtml) to load it. For more information about router-outlet click here.
78. So we have created the Application Component (AppComponent), let’s go to AppModule and register HomeComponent and AppComponent along routing table. After that we will add AppComponent to bootstrap, in order to do this all, update your app.module.ts according to following:

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import { NgModule } from '@angular/core';
import { APP_BASE_HREF } from '@angular/common';
import { BrowserModule } from '@angular/platform-browser';
import { ReactiveFormsModule } from '@angular/forms';
import { HttpModule } from '@angular/http';
import { AppComponent } from './app.component';
import { routing } from './app.routing';
import { HomeComponent } from './components/home.component';

 
@NgModule({
    imports: [BrowserModule, ReactiveFormsModule, HttpModule, routing],
    declarations: [AppComponent, HomeComponent],
    providers: [{ provide: APP_BASE_HREF, useValue: '/' }],
    bootstrap: [AppComponent]
})

export class AppModule { }

77. You can see, we imported the HomeComponent and AppComponent, added it in declaration and bootstrapping the AppComponent as entry point to our application. (Bootstrapping is more than just an entry point as discussed in the previous steps, you can search on Google to fully understand it. Here for simplicity, I am only referring it as the entry point).
78. We are almost there to run our Angular2 application and view the Home page. Go to Views -> Home and double click on Index.cshtml to edit it:

78. Delete the existing code and enter following lines of code:

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@{
    ViewBag.Title = "Index";
}

<body>
    <user-app>Loading…<user-app>
</body>

79. user-app is the selector for AppComponent, this is how we use the Component in HTML:

80. Next in Solution Explorer, double click on systemjs.config.js and at the bottom add main.jsin packages section:

81. Run the project, you should see following web application with Home page and large image, you can see in address bar the page URL is ending with home that is same URL we defined in routing table for Home page:

82. So far, we have created basic architecture for Angular2 in ASP.NET MVC application with one static page. Next step is to create the User Management page that includes loading all users, adding new user, updating and deleting existing user:

83. In User Management page, we will use TypeScript Interface (for User Model), Reactive forms and one third party component Ng2-Bs3-Modal for modal pop up.
    1. Interface: An interface is an abstract type, it does not contain any code as a class does. It only defines the signature or shape of an API that’s why we will use interface to define our User Model.
    2. Reactive Forms: Angular2 provides two kind of forms, Template driven and Reactive Forms (Model Driven Forms). There is a great article available for both forms here & here. if you are ASP.NET MVC developer, Reactive Forms is like MVC strongly typed Razor view.
84. Next lets create the user interface. Right click on app folder and select Add -> New Folder. Enter the name of folder as Models:

85. Right click on newly created Models folder and select Add -> TypeScript File, enter the file name as user.ts:

86. Enter the following variables in newly created user interface:

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export interface IUser {
    Id: number,
    FirstName: string,
    LastName: string,
    Gender: string
}

87. These interface properties are same as User table in database. The awesome thing about Angular2 is, user object will automatically be mapped to array of IUser interface when we will load data from database through RESTful API, in next steps, we will see how this is being done.
88. Before moving to UserComponent, lets create some helping files i.e. Global variables and Enumeration. I prefer to save all endpoints, error message and other shared variables in Global file and I am going to create Enumeration for CRUD operation. Right click on app folder and select Add ->New Folder, name the folder as shared:

89. Right click on newly created shared folder and select Add -> TyepScript File, enter the name as global.ts:

90. Copy the following code in global.ts:

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export class Global {
    public static BASE_USER_ENDPOINT = 'api/userapi/';
}

91. This is simple exportable class with single static property BASE_USER_ENDPOINT having the base endpoint for user management RESTful APIs.
92. Again, right click on shared folder and select Add -> TypeScript File, enter the name as enum.ts:

93. Enter following code in enum.ts file:

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export enum DBOperation {
    create = 1,
    update = 2,
    delete =3
}

94. Enumeration is quite self-explanatory, instead of hard coded string for CRUD operations (“create”, “update”,”delete”), we would use DBOperation enumeration.
95. Next, let’s create the important functions to call ASP.NET RESTful Web API for user management using Angular2 HTTP service. As discussed in previous steps, we will create GET, POST, PUT and DELETE requests for RESTful users APIs that we already have created using ASP.NET MVC Web API in earlier steps. Right click on app folder and select Add -> New Folder, enter the name as Service.

96. Right click on newly created Service folder and select Add -> TypeScript File, enter the name as user.service.ts:

97. Copy the following code in user.service.ts file:

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import { Injectable } from '@angular/core';
import { Http, Response, Headers, RequestOptions} from '@angular/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/do';
import 'rxjs/add/operator/catch';

@Injectable()
export class UserService {
  constructor(private _http: Http) { }

  get(url: string): Observable<any> {
    return this._http.get(url)
      .map((response: Response) => <any>response.json())
      // .do(data => console.log("All: " + JSON.stringify(data)))
      .catch(this.handleError);
  }

  post(url: string, model: any): Observable<any> {
    let body = JSON.stringify(model);
    let headers = new Headers({ 'Content-Type': 'application/json' });
    let options = new RequestOptions({ headers: headers });
    return this._http.post(url, body, options)
      .map((response: Response) => <any>response.json())
      .catch(this.handleError);
  }

  put(url: string, id: number, model: any): Observable<any> {
    let body = JSON.stringify(model);
    let headers = new Headers({ 'Content-Type': 'application/json' });
    let options = new RequestOptions({ headers: headers });
    return this._http.put(url+id, body, options)
      .map((response: Response) => <any>response.json())
      .catch(this.handleError);
  }

  delete(url: string, id: number): Observable<any> {
    let headers = new Headers({ 'Content-Type': 'application/json' });
    let options = new RequestOptions({ headers: headers });
    return this._http.delete(url+id,options)
      .map((response: Response) => <any>response.json())
      .catch(this.handleError);
  }

  private handleError(error: Response) {
    console.error(error);
    return Observable.throw(error.json().error || 'Server error');
  }

}

In order to understand above code, we need to learn about Observable, you can easily get information about it just by searching it on Google but I would prefer to quickly go through following link:

https://scotch.io/tutorials/angular-2-http-requests-with-observables

99. In just few line, Observable is more like data stream, opposite to promise method (in Angular 1.x), Observable doesn’t return the response at once but in stream, it provides very helpful methods e.g. map(for mapping result to interface), filter(filter any particular record from array of data) etc. Observablealso provides HTTP request handling. Rxjs is an eternal library providing us all Observable methods.
100. The first method is get, that is taking the RESTful API URL as a parameter and returning the Observable<any>, you can also specify the particular type of interface to return e.g. Observable<IUser[]> but I try to keep it generic. In next lines, http get method is being called by providing the input RESTful API user, calling the map method to map the JSON response to any type, you can specify the particular type too like <IUser[]>response.json(). The type any is like a dynamic in C#, it does the compile type check.

  

104. One awesome thing about RESTful API is the HTTP verbs like functions names i.e. if function name is starting from GET, PUT, POST or DELETE, we only need base URL (endpoint), by the HTTP call, it automatically determines the corresponding function. It’s obvious, one Web API controller should have one HTTP verb method.
105. The other methods POST, PUT and DELETE have almost same function body, creating the http header and sending the IUser interface in body where it is being received in Web API controller functions and automatically get converted to user entity because column name does match.
106. Now that we created the user service, let’s add it to AppModule. Double click on app.module.ts file in app folder to edit it. Import the UserService by adding following line:

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import { UserService} from './Service/user.service'

104. Add the UserService in AppModule providers section.

105. After this, let create the UserComponent. Right click on Components folder and select Add -> TypeScript File:

106. Enter the name as user.component.ts:

107. We will create the template in separate html file so right click on Components folder again select Add-> HTML Page:

108. Enter the name as user.component.html:

109. Before going to UserComponent, let configure one third party component for modal pop ng2-bs3-modal. It’s very simple to use.
110. Double click on Package.json file in Angular2MVC project and add following package in devDependencies section:

"ng2-bs3-modal": "0.10.4"

111. Now let’s download this package from NPM, right click on package.json and select Restore Packages:

112. Double click on systemjs.config.js in Angular2MVC project:
113. Add the following text in map section:

'ng2-bs3-modal': 'npm:/ng2-bs3-modal'

114. Add the following text in packages section:

           'ng2-bs3-modal':

           { main: '/bundles/ng2-bs3-modal.js', defaultExtension: 'js' }

115. Final update should look like following:

116. Now since we got our modal pop up, let’s create the UserComponent that will have view all users, add new user, edit and delete existing users. Double click on user.component.ts file in app -> components folder to edit:

117. First add following import statements:

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import { Component, OnInit, ViewChild } from '@angular/core';
import { UserService } from '../Service/user.service';
import { FormBuilder, FormGroup, Validators } from '@angular/forms';
import { ModalComponent } from 'ng2-bs3-modal/ng2-bs3-modal';
import { IUser } from '../Model/user';
import { DBOperation } from '../Shared/enum';
import { Observable } from 'rxjs/Rx';
import { Global } from '../Shared/global';

118. We are importing Components, OnInit (to use OnInit event), ViewChild (to access Modal pop up properties).
119. Then we are importing the UserSerivce that executes the HTTP calls to server.
120. In UserComponent we are going to use Reactive (Model-driven) forms that I found way more organized and easy to use than template driven forms. To me, it looks like a strongly type ASP.NET MVC razor view, it is also good for unit testing. The form fields, validations and validation errors can be managed on TypeScript side and HTML view has minimum form logic that is good practice to keep the code at one place. To read more about Reactive form, click here.
121. ModalComponent is third party modal pop up that we downloaded in previous steps.
122. IUser is the interface we will use as a Model, to store the user information.
123. DBOperation and Global are enumeration and global variables.
124. Observable, we briefly discussed in previous steps. We will use subscribe and filter function from Rxjs library.
125. Next copy following Component meta data information under the import statements:

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@Component({
    
templateUrl: 'app/Components/user.component.html'

})

126. Since User is a parent component and we will not use it in any other component, we are not specifying the Selector property. HTML for User component would be in user.component.html file.
127. Next let’s start the UserComponent class body and declare the required variable:

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export class UserComponent implements OnInit 
{
    @ViewChild('modal') modal: ModalComponent;
    users: IUser[];
    user: IUser;
    msg: string;
    indLoading: boolean = false;
    userFrm: FormGroup;
    dbops: DBOperation;
    modalTitle: string;
    modalBtnTitle: string;
}

128. We are starting our class with export and then with our UserComponent name, since we will use onInit event, our class should must implement this.
129. The next line is starting with @ViewChild(‘modal’), the modal is placeholder for Modal pop up component that we will create in HTML template. This is the syntax if you want to access any HTML element in TypeScript. :ModalComponent specify the type of element.
130. Next we are creating the array of IUser interface to hold the list of users and singe IUser to hold one user information for add, edit and delete. Others are few string and Boolean variables that we will use in next steps to show some messages.
131. As we discussed in previous steps, we will use Reactive(Model-driven) form, so we create the userformof Formgroup type.
132. Next is to add the constructor for UserComponent class:

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constructor(private fb: FormBuilder, private _userService: UserService) { }

133. On great thing about Angular2 is dependency injection, in constructor you can see, we are getting the FormBuilder and UserService instances though DI. To read more about DI, click here.
134. So far, our UserComponent should look like following:

135. At this point, you might be getting an error because still ngOnInit event is not implemented, let’s go ahead and add ngOnInit event, we will create and initialize our Reactive User form:

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ngOnInit(): void {

        this.userFrm = this.fb.group({
            Id: [''],
            FirstName: ['', Validators.required],
            LastName: [''],
            Gender: ['']
        });
        
       this.LoadUsers();
    
     }

136. We are initializing the User form, specifying the form elements and validation rules. Right now form is initialized with empty string ‘’.
137. Next let create the LoadUsers method, as name says, this method will call the get method from UserService to load all users from database through RESTful API:

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LoadUsers(): void {
           this.indLoading = true;
           this._userService.get(Global.BASE_USER_ENDPOINT)
            .subscribe(users => { this.users = users; this.indLoading = false; },
            error => this.msg = <any>error);

           }

136. Subscribe is the part of Observable that we discussed in previous steps. Once the user loads would be complete, it will save it in users variable. In case of any error, error message would be saved in msgvariable. indLoading is the Boolean variable we are using here to show loading message until full response would be loaded.
137. Next, let’s add three methods to show modal pop up for Add, Update and Delete user. Add following code for these functions:

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addUser() {
       this.dbops = DBOperation.create;
       this.SetControlsState(true);
       this.modalTitle = "Add New User";
       this.modalBtnTitle = "Add";
       this.userFrm.reset();
       this.modal.open();
   }

   editUser(id: number) {
       this.dbops = DBOperation.update;
       this.SetControlsState(true);
       this.modalTitle = "Edit User";
       this.modalBtnTitle = "Update";
       this.user = this.users.filter(x => x.Id == id)[0];
       this.userFrm.setValue(this.user);
       this.modal.open();
   }

   deleteUser(id: number) {
       this.dbops = DBOperation.delete;
       this.SetControlsState(false);
       this.modalTitle = "Confirm to Delete?";
       this.modalBtnTitle = "Delete";
       this.user = this.users.filter(x => x.Id == id)[0];
       this.userFrm.setValue(this.user);
       this.modal.open();
   }

136. These all methods are resembling so let’s take AddUser method and understand it. First, we are storing current DB operation in dpops variable that is of DBOperation enumeration type. Next, we are calling SetControlsState method that will enable or disable form controls. Next variables are setting the modal pop up heading and button title. In only AddUser function, we are resetting form to clearing the form. Next, we are calling modal.open() function to view the modal pop up. In edit and delete user method, we are getting UserID as parameter, calling the Observable’s filter method to get single user from users list. The filter syntax is like anonymous method in C#. the next line is to assign the single user to user form that will set the value to the front end, piece of cake.
137.  Let’s create the SetControlsState that will enable or disable the form. Reactive form has enable and disable methods that make the control read-only and editable.

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SetControlsState(isEnable: boolean)
{
 isEnable ? this.userFrm.enable() : this.userFrm.disable();
}

136.  The next method is onSubmit that actually get the form values and based on DBOperationenumeration value, it performs add, update and delete operation, we are using simple switch statement, paste following code:

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onSubmit(formData: any) {
    this.msg = "";
  
    switch (this.dbops) {
      case DBOperation.create:
        this._userService.post(Global.BASE_USER_ENDPOINT, formData._value).subscribe(
          data => {
            if (data == 1) //Success
            {
              this.msg = "Data successfully added.";
              this.LoadUsers();
            }
            else
            {
              this.msg = "There is some issue in saving records, please contact to system administrator!"
            }
             
            this.modal.dismiss();
          },
          error => {
           this.msg = error;
          }
        );
        break;
      case DBOperation.update:
        this._userService.put(Global.BASE_USER_ENDPOINT, formData._value.Id, formData._value).subscribe(
          data => {
            if (data == 1) //Success
            {
              this.msg = "Data successfully updated.";
              this.LoadUsers();
            }
            else {
              this.msg = "There is some issue in saving records, please contact to system administrator!"
            }

            this.modal.dismiss();
          },
          error => {
            this.msg = error;
          }
        );
        break;
      case DBOperation.delete:
        this._userService.delete(Global.BASE_USER_ENDPOINT, formData._value.Id).subscribe(
          data => {
            if (data == 1) //Success
            {
              this.msg = "Data successfully deleted.";
              this.LoadUsers();
            }
            else {
              this.msg = "There is some issue in saving records, please contact to system administrator!"
            }

            this.modal.dismiss();
          },
          error => {
            this.msg = error;
          }
        );
        break;

    }
  }

136. The code is quite simple and self-explanatory, once we submit the form, it sends all the values that we can get through .value property. That’s pretty much it on TypeScript side.
137. Let’s write the HTML template for UserComponent. Double click on user.component.html to edit it:

 

136.  Copy the following code in user.component.html:

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<div class='panel panel-primary'>
  <div class='panel-heading'>
    User Management
  </div>
  <div class='panel-body'>
    <div class='table-responsive'>
      <div style="padding-bottom:10px"><button class="btn btn-primary" (click)="addUser()">Add</button></div>
      <div class="alert alert-info" role="alert" *ngIf="indLoading"><img src="../../images/loading.gif" width="32" height="32" /> Loading...</div>
      <div *ngIf='users && users.length==0' class="alert alert-info" role="alert">No record found!</div>
      <table class='table table-striped' *ngIf='users && users.length'>
        <thead>
          <tr>
            <th>First Name</th>
            <th>Last Name</th>
            <th>Gender</th>
            <th></th>
          </tr>
        </thead>
        <tbody>
          <tr *ngFor="let user of users">
            <td>{{user.FirstName}}</td>
            <td>{{user.LastName}}</td>
            <td>{{user.Gender}}</td>
            <td>
              <button title="Edit" class="btn btn-primary" (click)="editUser(user.Id)">Edit</button>
              <button title="Delete" class="btn btn-danger" (click)="deleteUser(user.Id)">Delete</button>
            </td>
          </tr>
        </tbody>
      </table>
      <div>
      </div>
    </div>
    <div *ngIf="msg" role="alert" class="alert alert-info alert-dismissible">
      <button type="button" class="close" data-dismiss="alert" aria-label="Close"><span aria-hidden="true">&times;</span></button>
      <span class="glyphicon glyphicon-exclamation-sign" aria-hidden="true"></span>
      <span class="sr-only">Error:</span>
      {{msg}}
    </div>
  </div>
</div>

<modal #modal>
  <form novalidate (ngSubmit)="onSubmit(userFrm)" [formGroup]="userFrm">
    <modal-header [show-close]="true">
      <h4 class="modal-title">{{modalTitle}}</h4>
    </modal-header>
    <modal-body>

      <div class="form-group">
        <div>
          <span>Full name*</span>
          <input type="text" class="form-control" placeholder="First Name" formControlName="FirstName">
        </div>
        <div>
          <span>Full name</span>
          <input type="text" class="form-control" placeholder="Last Name" formControlName="LastName">
        </div>
        <div>
          <span>Gender*</span>
          <select formControlName="Gender" class="form-control">
            <option>Male</option>
            <option>Female</option>
          </select>
        </div>
      </div>
    </modal-body>
    <modal-footer>
      <div>
        <a class="btn btn-default" (click)="modal.dismiss()">Cancel</a>
        <button type="submit" [disabled]="userFrm.invalid" class="btn btn-primary">{{modalBtnTitle}}</button>
      </div>
    </modal-footer>
  </form>
</modal>

136.  If you look at the Add button, we are calling the AddUser function by using (click) function that is the example of event binding we discussed in previous steps.
137.  Next, we are using *ngIf, the structural directives to show the loading message based on indLoading Boolean variable.
138. Next, we are using *ngFor structural directive to loop through the users array and showing the user information.
139.  Next code is for modal pop up, you can see #modal placeholder that we are using to access it on TypeScript side through @ViewChild to access open and dismiss functions.
140. Next we are creating the form, (ngSumbit) event will send the form data to TypeScript onSumitfunction.
141.  Through [formgorup] property binding we are assigning the userform that we created on TypeScript side. We are telling our template the corresponding form control through formControlName property.
142. Add and Edit buttons will be disabled until form gets valid. This is being handled by [disabled] property binding until userform.invalid property get enabled.
143. That’s it with UserComponent, now let’s add the routing for UserComponent and add the it AppModule.
144. Double click on app.routing.ts in app folder to edit it:

136.  Import the UserComponent by following code:

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import { UserComponent } from './components/user.component';

136.  Add the UserComponent route as following:

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{ path: 'user', component: UserComponent }

136. The final app.routing.ts should look like following:

136. Edit the app.component.ts by double clicking on it:

136. Add User Component in App Module:

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import { UserComponent } from './components/user.component';

136. Add the UserComponent in declaration section, the final AppModule should look like following:

136. Add menu item for User Management, double click on app.component.ts and add following line:

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<li><a [routerLink]="['user']">Users Management</a></li>

136.  Final app.component.ts should be following:

136. Compile and run the application.