ASP.NET Web API

Contents
 What & Why ASP.NET Web API
 A look at Rest & Soap
 Basic Web API Structure
 Web API Routing & Actions
 Validation
 Odata
 Content Negotiation
 Http Client

ASP.NET Web API
 ASP.NET Web API is a framework for building http
based services in top of .net framework.
 WCF  Care about transport flexibility.
 WebAPI  Care about HTTP

Build Richer Apps
Reach More Clients

 Reach more clients
 Client appropriate format
 Embrace http
 Use http as an application protocol
 Amazon has both Rest and Soap based services
and 85% of the usage is Rest based.

 SOAP
 A specification
 Rest
 A set of architectural principal
 Resource Oriented Architecture
 Resources
 Their names(URIs)
 Uniform Intercace

 Asmx
 Ws*
 Wcf
 Wcf 3.5
 Wcf rest starter kit
 Wcf Rest service
 ASP.Net Web API

Web API - 1 slide
public class ValueController : ApiController
{
// GET <controller>
public string Get()
{
return "Demo result at " + DateTime.Now.ToString();
}
}
protected void Application_Start(object sender, EventArgs e)
{
GlobalConfiguration.Configuration.Routes.Add("default",
new HttpRoute("{controller}"));
}

Microsoft
/web
®
Sample Read-only Model and Controller

Microsoft
/web
®
Read-only Controller Actions to return data

Microsoft
/web
®
Routing a Web API Using Global.asax.cs

Routing and Actions
 Web API uses the HTTP method, not the URI path,
to select the action.
 To determine which action to invoke, the framework
uses a routing table.
routes.MapHttpRoute(
name: "API Default",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);

 If no route matches, the client receives a 404 error.
 Custom name mapping to http actions.
[HttpGet]
public Product FindProduct(id) {}

 or can override the action name by using
the ActionName attribute.
 api/products/thumbnail/id
[HttpGet]
[ActionName("Thumbnail")]
public HttpResponseMessage
GetThumbnailImage(int id);

 To prevent a method from getting invoked as an
action, use the NonAction attribute.
// Not an action method.
[NonAction]
public string GetPrivateData() { ... }

Exception Handling
 By default, most exceptions are translated into an HTTP response
with status code 500, Internal Server Error.
public Product GetProduct(int id)
{
Product item = repository.Get(id);
if (item == null)
{
var resp = new
HttpResponseMessage(HttpStatusCode.NotFound)
{
Content = new StringContent(string.Format("No product with ID
= {0}", id)),
}
throw new HttpResponseException(resp);
}
return item;
}

 HTTP/1.1 404 Not Found
Content-Type: application/json; charset=utf-8
Date: Thu, 09 Aug 2012 23:27:18 GMT
Content-Length: 51
{
"Message": “No product with id = 12 not found"
}

 You can customize how Web API handles exceptions by
writing an exception filter.
public class NotImplExceptionFilterAttribute :
ExceptionFilterAttribute
{
public override void
OnException(HttpActionExecutedContext context)
{
if (context.Exception is NotImplementedException)
{
context.Response = new
HttpResponseMessage(HttpStatusCode.NotImplemented);
}
}
}

There are several ways to register a Web API
exception filter:
 By action
 By controller
 Globally
[NotImplExceptionFilter]
GlobalConfiguration.Configuration.Filters.Add(
new
ProductStore.NotImplExceptionFilterAttribute());

Validation
 public class Product
{
public int Id { get; set; }
[Required]
public string Name { get; set; }
public decimal Price { get; set; }
[Range(0,999)]
public double Weight { get; set; }
}

 if (ModelState.IsValid)
{
return new
HttpResponseMessage(HttpStatusCode.OK);
}
else
{
return new
HttpResponseMessage(HttpStatusCode.BadReques
t);
}

 public class ModelValidationFilterAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(HttpActionContext actionContext)
{
if (actionContext.ModelState.IsValid == false)
{
var errors = new Dictionary<string, IEnumerable<string>>();
foreach (KeyValuePair<string, ModelState> keyValue in
actionContext.ModelState)
{
errors[keyValue.Key] = keyValue.Value.Errors.Select(e =>
e.ErrorMessage);
}
actionContext.Response =
actionContext.Request.CreateResponse(HttpStatusCode.BadReq
uest, errors);
}
}
}

 HTTP/1.1 400 Bad Request
Server: ASP.NET Development Server/10.0.0.0
Date: Fri, 20 Jul 2012 21:42:18 GMT
Content-Type: application/json; charset=utf-8
Content-Length: 239
Connection: Close
{
"product": [
"Required property 'Name' not found in JSON. Line 1, position 18."
],
"product.Name": [
"The Name field is required."
],
"product.Weight": [
"The field Weight must be between 0 and 999."
]
}

 GlobalConfiguration.Configuration.Filters.Add(new
ModelValidationFilterAttribute());
 [ModelValidationFilter]

 public class Product
{
[JsonIgnore]
public int ProductCode { get; set; } // omitted
}

 [DataContract]
public class Product
{
[DataMember]
[DataMember]
public int ProductCode { get; set; } // omitted by
default
}

OData
http://localhost/Products?$orderby=Name
The EnableQuerySupport method enables query
options gloablly for any controller action that
returns anIQueryable type.
 To enable only for specific action/controller
[Queryable]
IQueryable<Product> Get() {}

Option Description
$filter
Filters the results, based on a Boolean
condition.
$inlinecount
Tells the server to include the total count
of matching entities in the response.
(Useful for server-side paging.)
$orderby Sorts the results.
$skip Skips the first n results.
$top Returns only the first n the results.
:

 http://localhost/odata/Products?$orderby=Category,
Price desc
[Queryable(PageSize=10)]
public IQueryable<Product> Get()
{
return products.AsQueryable();
}
[Queryable(AllowedQueryOptions=
AllowedQueryOptions.Skip |
AllowedQueryOptions.Top)]

Content Negotiation
 The process of selecting the best representation for
a given response when there are multiple
representations available.
 Accept:
 Accept-Charset:
 Accept-Language:
 Accept-Encoding:

HttpClient
 HttpClient is a modern HTTP client for ASP.NET Web
API. It provides a flexible and extensible API for
accessing all things exposed through HTTP.
 HttpClient is the main class for sending and
receiving HttpRequestMessages and
HttpResponseMessages.
 Task based pattern
 Same HttpClient instance can be used for multiple
URIs even from different domains.

Self Reading
 Authentication and Authorization
 Extensibility
 Tracing and Debugging

ASP.NET Web API

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