Cross-Origin Requests (CORS) in ASP.NET Web API 2

Hello frnds,

In my previous post CRUD with AngularJS and ASP.Net Web API, I tried to show you, how to perform CRUD using AngularJs and ASP.NET web API.
In this example we had a ASP.NET Web API called 'Book API' and AngularJs views which talks to book api. As part of this example our web api and angularjs view both were part of same application. It means application and APIs both are running under same domain and port.

Now imagine, if our Book APIs are hosted in other domain and we need to consume it through AngularJS or Javascript/jquery app deployed/running in different domain. Problem looks very simple but fact is that we can't perform cross-origin/domain communication. So how to tackle this cross origin calls then, and the answer is using CORS  in ASP.NET Web API 2.





What is CORS?
Cross Origin Resource Sharing (CORS) is a W3C standard that allows a server to relax the same-origin policy. Using CORS, a server can explicitly allow some cross-origin requests while rejecting others. CORS is safer and more flexible than earlier techniques such as JSONP.

What is "Same Origin"?
Two URLs have the same origin if they have identical schemes, hosts, and ports. (RFC 6454)
These two URLs have the same origin:
http://example.com/foo.html
http://example.com/bar.html

These URLs have different origins than the previous two:
http://example.net - Different domain
http://example.com:9000/foo.html - Different port
https://example.com/foo.html - Different scheme
http://www.example.com/foo.html - Different subdomain

For details please visit: Enabling Cross-Origin Requests in ASP.NET Web API 2.

Now let's do the example.
On first step what we will do is, deploy our Book API (which we have created as part of above mentioned post 'CRUD with AngularJS and ASP.Net Web API'. and then our target will be to consume BooKAPIs from another application hosted with different domain or port.
I deployed my BookAPI to IIS and URL for BooKAPI for me is: "http://localhost:80/AngularJSExample/api/BookAPI".

Next let's create a simple asp.net application. For simplicity, In this application I am going to have a simple html page called "Home.html" and in this I wrote jqury code to access the BookAPI url to display all the books. Here is the code for Home.html.

<head>
    <title>CORS Example</title>
</head>
<body>
    <script src="Scripts/jquery-2.1.4.min.js"></script>
    <button id="btnGetBooks">Get Books</button>
    <div id="bookDiv"></div>
    
    <script>
        $(function () {

            var getBookList = function () {
                $.get(url).success(displayBooks).fail(displayErrors);
            };

            var displayBooks = function (data) {
                for (i = 0; i < data.length;i++) {
                    $("#bookDiv").append('Id=' + data[i].Id + ' Name=' + data[i].Name + ' Author=' + data[i].Author + '<br/>');
                }
            }

            var displayErrors = function (data) {
                $("#bookDiv").append(JSON.stringify(data, null, 1));
            }

            var url = "http://localhost/AngularJSExample/api/BookAPI"

            $("#btnGetBooks").click(getBookList);
        });
    </script>
</body>
</html>

Here is the UI for above code:

In above html, we have a button and on click of this button application will fetch books detail from BookAPI running under http://localhost:80/AngularJSExample/api.

In Html, I have a div which will show the result. On click of button I am calling the BookAPI using jquery $.get() method. For jquery, either you install directly to your application using nuget packages and refer it Or you can directly refer it through online CDN links.




Now I run it and click on 'Get Books' button then this is what you will see in page as output.

It means BookAPI is not allowing cross-origin communication. For your attention though both the application running under same host but ports are different. BookAPI running under port 80 and Home.html application running under port 81 and that's why asp.net web api (bookapi) is refusing the connection requested by port 81.
Here ASP.NET Web API 2 introduced the feature of CORS which makes our life easier on cross-origin connections.

To enable CORS feature for our BookAPI we need to follow few steps. Let's do it.

Follow below mentioned steps to enable CORS for your web api.
1. Install "Microsoft ASP.NET Web API  CORS" package using nuget package manager to you web api application project(please refer below screenshot here)

2. Open WebApiConfig.cs add settings to enable Cors by registering it to work it globally for all api controllers. To do this add below line of code to your 'Register' method:

config.EnableCors(new EnableCorsAttribute("*", "*", "GET"));

Here
first parameter '*' says, allows any orgin,
second parameter '*' says, allows any header,
third parameter 'GET' says, allows only GET methods.

3. OR go to individual API controller and enable it at controller/action method level and add 'EnableCors' attribute to the controller/action method as defined here:

[EnableCors("*","*","GET")]

'EnableCors' attribute presents under 'System.Web.Http.Cors' dll. So you include this you controller as

using System.Web.Http.Cors;

4. Deploy/update your app to IIS.

Now run Home.html page which we created as separate application and click on 'Get Books' button. Here is the result which we get:

That's it.

Thank You for reading. Feel free to give your feedback/comment.

CRUD with AngularJS and ASP.Net Web API

It's really fun to learn something new and the more fun is in sharing it with people.
So here I am gonna explain you "How to perform CRUD with AngularJS using Asp.net Web API". AngularJS become such a hot client side technology in today's web world and believe me it's going to rule the web application development.
Before I start let's know a bit about basic of AngularJS.

What is AngularJS
AngularJS is a library written in JavaScript. It's an open-source web application framework developed and maintained by Google It helps to create single-page applications(SPA) that only requires HTML, CSS and Javascript on client side.
Do not compare it with JQuery, It uses a subset of JQuery to perform some task. So whenever you want/need to install AngularJS for your project then Install/include JQuery library first and then AngularJS.
To know more about AngularJS: https://docs.angularjs.org/guide/introduction

AngularJS extends HTML with ng-directive and the basic directives are:

• ng-app: defines an AngularJS application.
• ng-model: binds the value of HTML controls (input, select, textarea) to application data.
• ng-bind: binds application data to the HTML view.
• ng-controller: defines the application controller.

Apart from these basics directive I am going to use some concepts of AngularJS like Module, Service, Expressions etc. I would suggest if you have patience then better to spend some time here: http://www.w3schools.com/angular/

Hope by now you have learned about basics of AngularJS. So let's start with CRUD operation example.
where to start?????  Ok let's start with building Web API first which basically will perform CRUD with database. For the example purpose I have not used any database here but your Web Api will be the one which is going to interact with your database.
In short, ASP.NET Web API is a framework for building web APIs on top of the .NET Framework over http protocol. To know more about ASP.NET Web API refer this: http://www.asp.net/web-api.

To Create a ASP.NET Web API using Visual Studio 2013, create a new project => Web => ASP.NET Web Application and then select the template Web API.
(I assume, you are very much familier with visual studio tool and MVC framework and that's why I am not including any screenshot here for this.)


Once you create the project, Let's add a model class "Book.cs" under Model folder.

public class Book
    {
        public string Id { get; set; }
        public string Name { get; set; }
        public string Author { get; set; }
        public decimal Price { get; set; }
    }

Then add a APIController with empty template for this, by right clicking of 'Controller' folder and name it "BookAPIController".

public class BookAPIController : ApiController
    {
        private static IList<Book> books = new List<Book>()
        {
            new Book{Id = "A01", Name = "Once upon a time", Author = "G D Roy", Price = 150.00M},
            new Book{Id = "A02", Name = "The Last Hero", Author = "K P Say", Price = 150.00M},
            new Book{Id = "A03", Name = "The King of Kingdom", Author = "Albert D", Price = 150.00M},
            new Book{Id = "A04", Name = "Jungle King", Author = "D Serduke", Price = 150.00M},
            new Book{Id = "A05", Name = "Magical Box", Author = "M Mathews", Price = 150.00M}
        };

        // GET: api/BookAPI
        public IEnumerable<Book> GetBooks()
        {
            return books;
        }

        // GET: api/BookAPI/5
        public Book GetBook(string id)
        {
            return books.FirstOrDefault<Book>(book => book.Id == id);
        }

        // POST: api/BookAPI
        public HttpResponseMessage PostBook(Book book)
        {
            books.Add(book);
            return Request.CreateResponse(HttpStatusCode.OK);
        }

        // PUT: api/BookAPI/5
        public HttpResponseMessage PutBook(Book book)
        {
            if(books.Any<Book>(bk => bk.Id == book.Id))
            {
                try
                {
                    Book currentBook = books.First<Book>(bk => bk.Id == book.Id);
                    int index = books.IndexOf(currentBook);
                    books[index] = book;
                    return Request.CreateResponse(HttpStatusCode.OK);
                }
                catch(Exception ex)
                {
                    throw new HttpResponseException(Request.CreateResponse(HttpStatusCode.NotFound));  
                }
            }
            else
            {
                return Request.CreateResponse(HttpStatusCode.NotFound);
            }
        }

        // DELETE: api/BookAPI/5
        public HttpResponseMessage DeleteBook(string id)
        {
            if (books.Any<Book>(bk => bk.Id == id))
            {
                try
                {
                    Book currentBook = books.First<Book>(bk => bk.Id == id);
                    int index = books.IndexOf(currentBook);
                    if(books.Remove(currentBook))
                        return Request.CreateResponse(HttpStatusCode.OK);
                    else
                        return Request.CreateResponse(HttpStatusCode.InternalServerError);
                }
                catch (Exception ex)
                {
                    throw new HttpResponseException(Request.CreateResponse(HttpStatusCode.NotFound));
                }
            }
            else
            {
                return Request.CreateResponse(HttpStatusCode.NotFound);
            }
        }
    }

In above code, each and every method tells about himself.
Note: WEB API works on Get, Post, Put and Delete http methods.
So our Web API is ready and can be consumed by client.

Now we will actually talk about AngularJS framework to do the CRUD operation without any postback. Here we go:
 Let's add below mentioned three javascript file under 'Script' folder by creating a sub folder 'BookngScripts'. This sub folder is optional but it become necessary to separate out your files with other jquery and angular js files.

1. BookngService.Js: This is AngularJS service which will basically consume the ASP.NET Web API and works as a middle layer between AngularJS controller and ASP.NET Web API.
2. BookngModule.Js: It's a container for the different parts of an application. All application controller should belong to a module.
3. BookngController.js: Controller is a JavaScript Object, created by a standard JavaScript object constructor.

Now we write code for above mentioned items:
BookngService.js
app.service('bookManageService', function ($http) { 

    //Add New Book
    this.post = function (Book) {
        var request = $http({
            method: "post",
            url: "/api/BookAPI",
            data: Book
        });
        return request;
    }

    //Fetch Book
    this.get = function (Id) {
        return $http.get("/api/BookAPI/" + Id);
    }

    //Fetch All Books
    this.getAllBook = function () {
        return $http.get("/api/BookAPI");
    }

    //Update Book  
    this.put = function (Book) {
        var request = $http({
            method: "put",
            url: "/api/BookAPI",
            data: Book
        });
        return request;
    }

    //Delete Book  
    this.delete = function (Id) {
        var request = $http({
            method: "delete",
            url: "/api/BookAPI/" + Id
        });
        return request;
    }

});

Here I created a AngularJS service called "bookManageService". It defines AngularJS service methods like post, get, getAllBook, put and delete. This service methods will be called from AngularJS controller.
Note: $http is an AngularJS service for reading data from remote servers.

Now we create controller called "bookController":
BookngController.js
app.controller('bookController', function ($scope, bookManageService) {
    $scope.IsInEditMode = false; //variable to decide, edit a record or create a record 
    $scope.Message = ""; //variable used to store error or success messages.
    
GetAllBooks(); 

    //Get All Books
    function GetAllBooks() {
        var reqGet = bookManageService.getAllBook();
        reqGet.then(function (obj) { $scope.Books = obj.data },
            function (error) {
                $scope.Message = 'Error while fetching records. Error:' + error;
            });
    }

    //Clear Book Model
    function Clear() {
        $scope.IsInEditMode = false;
        $scope.Id = "";
        $scope.Name = "";
        $scope.Author = "";
        $scope.Price = "";
    }

    //Create or Edit Book
    $scope.save = function () {
        var Book = {
            Id: $scope.Id,
            Name: $scope.Name,
            Author: $scope.Author,
            Price: $scope.Price
        };
        if($scope.IsInEditMode == false){//Adding new book
            var reqPost = bookManageService.post(Book);
            reqPost.then(function (obj) {
                $scope.Message = "Book added successfully";
                GetAllBooks();
                Clear();
            },
            function (err) {  
                $scope.Message = "Adding Book failed for following reason:" + err;  
            }); 
        }
        else { //Editing existing book detail
            Book.Id = $scope.Id;
            var reqPost = bookManageService.put(Book);
            reqPost.then(function (obj) {
                $scope.Message = "Book updated successfully";
                GetAllBooks();
                Clear();
            },
            function (err) {
                $scope.Message = "Updating Book failed for following reason:" + err;
            });
        }
    }

    //Delete a Book
    $scope.delete = function (Book) {
        var reqDelete = bookManageService.delete(Book.Id);
        reqDelete.then(function (obj) {
            GetAllBooks();
            $scope.Message = "Book deleted successfully";  
        },
        function (err) {
            $scope.Message = "Deleting Book failed for following reason:" + err ;
        });
    }

    //Fetch book detail
    $scope.get = function (Book) {
        var reqGet = bookManageService.get(Book.Id);
        reqGet.then(function (obj) {
            var res = obj.data;
            $scope.Id = res.Id;
            $scope.Name = res.Name;
            $scope.Author = res.Author;
            $scope.Price = res.Price;

            $scope.IsInEditMode = true;
        },
        function (err) {
            $scope.Message = "Unable to fetch book detail for following reason:" + err;
        });
    }

    //To Clear all Inputs controls value.  
    $scope.clear = function () {
        $scope.IsInEditMode = false;
        $scope.Id = "";
        $scope.Name = "";
        $scope.Author = "";
        $scope.Price = "";
    }

});

Here created a controller with the name "bookController" and it also define a function as second parameter which takes two argument $scope ($scope is the application object, the owner of application variables and functions. In short, It's the glue between application controller and the view) and the "bookManageService" (one which we created above here). Inside the function, I have defined four event method $scope.save, $scope.get, $scope.delete and $scope.clear.
Now we will create module:
BookngModule.js:
 var app = angular.module('bookModule', []);

and now create a MVC controller called "BookController" and add a action method called "Index".
BookController.cs
public class BookController : Controller
    {
        // GET: Book
        public ActionResult Index()
        {
            return View();
        }
    }


Now right click inside this Index and Add View with Empty(without a model) template and copy-paste the below code in your view:
<html ng-app="bookModule"> 
@{
    ViewBag.Title = "Manage Books";
}

<body>
    <table id="tblContainer" ng-controller="bookController">
        <tr>
            <td>
                <table style="border: solid 2px Black; padding: 5px;">
                    <tr style="height: 30px; background-color:lightsteelblue; color: maroon;">
                        <th></th>
                        <th style="width:50px">ID</th>
                        <th style="width:150px">Name</th>
                        <th style="width:150px">Author</th>
                        <th style="width:50px">MRP Price</th>
                        <th style="width:50px"></th>
                        <th style="width:50px"></th>
                    </tr>
                    <tbody ng-repeat="book in Books">
                        <tr>
                            <td></td>
                            <td style="width:50px"><span>{{book.Id}}</span></td>
                            <td style="width:150px"><span>{{book.Name}}</span></td>
                            <td style="width:150px"><span>{{book.Author}}</span></td>
                            <td style="width:50px"><span>{{book.Price | currency}}</span></td>
                            <td>
                                <input type="button" id="Edit" value="Edit" ng-click="get(book)" />
                            </td>

                            <td>
                                <input type="button" id="Delete" value="Delete" ng-click="delete(book)" />
                            </td>
                        </tr>
                    </tbody>
                </table>

            </td>
        </tr>
        <tr></tr>
        <tr></tr>
        <tr>
            <td>
                <div style="color: red;">{{Message}}</div>
                <table style="border: solid 4px Red; padding: 2px;">
                    <tr>
                        <td></td>
                        <td>
                            <span>Id</span>
                        </td>
                        <td>
                            <input type="text" id="BookId" ng-model="Id" />
                        </td>
                    </tr>
                    <tr>
                        <td></td>
                        <td>
                            <span>Name</span>
                        </td>
                        <td>
                            <input type="text" id="bookName" ng-model="Name" />
                        </td>
                    </tr>
                    <tr>
                        <td></td>
                        <td>
                            <span>Author</span>
                        </td>
                        <td>
                            <input type="text" id="bookAuthor" ng-model="Author" />
                        </td>
                    </tr>
                    <tr>
                        <td></td>
                        <td>
                            <span>Price</span>
                        </td>
                        <td>
                            <input type="text" id="bookPrice" ng-model="Price" />
                        </td>
                    </tr>
                    <tr>
                        <td></td>
                        <td></td>
                        <td>
                            <input type="button" id="save" value="Save" ng-click="save()" />

                            <input type="button" id="Clear" value="Clear" ng-click="clear()" />
                        </td>
                    </tr>
                </table>

            </td>
        </tr>

    </table>
</body>
</html>  
<script src="~/Scripts/angular.min.js"></script>
<script src="~/Scripts/angular-route.min.js"></script>
<script src="~/Scripts/BookngScripts/BookngModule.js"></script>
<script src="~/Scripts/BookngScripts/BookngController.js"></script>
<script src="~/Scripts/BookngScripts/BookngService.js"></script>

If you see the highlighted piece of code, you will realized how your view is connected with the AngularJS controller which we created here and how your model data is getting bind with UI. Anyway let me give some note about the directives highlighted here:

1. ng-app : this defines the module for our html page. 
2. ng-controller: this allows me to define the controller for this module.
3. {{xyz}}: this is the way to define an expression in AngularJS. You can also use such expression like {{5+2+3}}. Note: Instead of using expression to render value in html you can also use ng-bind directive. ex: <td style="width:50px"><span ng-bind="book.Id"></span></td>
4. ng-click: this directive allows you to bind the event(the one which we created in controller using $scope.get = function(..){....}) for button click.
5. ng-model: this bind the our model with view. So if view changes model will get updated automatically.

Here is the UI outcome of this:

That's it.

Thank You for reading. Feel free to give your feedback/comment.