Saturday, March 31, 2012

REST Services with ASP.NET Web API

Sometimes back, ASP.NET MVC 4 beta was release, this comes with quite a lot of capabilities to create mobile web applications with HTML5, to new features on Razor etc..
One of the milestones of this release is ASP.NET Web APIs, which allows developers to implement REST services. .NET 3.5/4.0 WCF provides us with the support of creating REST APIs using the webHttpBinding, however most of the features required to run the service needs the ASP.NET compatibility mode, this basically means the request to the REST service would first go through the ASP.NET pipeline, before being handed over to WCF. Then there was the WCF Web API, where Microsoft tried to re-define how REST services are created, but they opted in for moving REST support into ASP.NET and then to WCF, hence ASP.NET Web API, becomes the de facto technology for creating REST services. WCF WebHttpBinding would still exist, bu the recommendation is to to use Web APIs.

Implementing a Web API is simple, the steps involved are...
1) Create a MVC 4 project
2) Define a route for web APIs
2) Create a controller but that inherits from ApiController instead of Controller
4) Start writing those GET, POST, PUT and DELETE methods....

Once you have installed ASP.Net MVC 4, you can create a controller like this...

public class ProjectsController : ApiController

{

public IList GetProjects()

{

return GetProjectsFromDB();

}

public void PostProject(Project project)

{

SaveProjectIntoDB(project);

}

}


in your global file, you can create a route setting like this...

routes.MapHttpRoute(

name: "DefaultApi",

routeTemplate: "api/{controller}/{id}",

defaults: new { id = RouteParameter.Optional }

);

That's it you can open up a web browser or fiddler and make request, to call the method GetProjects(), you URL would be like this http://localhost:8080/api/Product. In fiddler you would see the JSON response similar to this....

{"EndDate":"\/Date(1333251468665+0530)\/","ProjectID":1,"ProjectName":"XYZ 12","ProjectType":"T&M","StartDate":"\/Date(1333251468665+0530)\/"},{"EndDate":"\/Date(1333251468665+0530)\/","ProjectID":2,"ProjectName":"JJ 777","ProjectType":"FB","StartDate":"\/Date(1333251468665+0530)\/"}

Now, if you know MVC, you would be asking me, you did not refer the action in the URL or in the route table, so how does asp.net know to invoke the GetProducts()?. The answer is the controller check to see the HTTP method the request arrived on, if it is a GET, the controller will try to match any controller method that starts with the word GET. This is the same convention for POST. For an example , the PostProject() method can be invoked by a call to the URL format http://localhost:8080/api/Product. As long as you make the request as a POST method, the PostProject() method will be called. This convention allows the concept of a resource being governed by one controller by the HTTP verbs GET, POST, DELETE and PUT.

With the default convention discussed above, if you want to have method that does not start with the word Get or multiple methods with the same signature starting with the word GET, you would have to specify a route for this and explicitly specify the action part in the URL. You would also need to attribute the methods with either HttpGet, HttpPost etc...

[HttpGet]

public IList<Project> ActiveProjects()

{

return GetProjectsFromDB(true);

}

Your route settings in the global file would be...

routes.MapHttpRoute(

name: "DefaultApiWithAction",

routeTemplate: "api/{controller}/{action}/{id}",

defaults: new { id = RouteParameter.Optional }


The URL format you would use to invoke this method would be

http://localhost:51499/api/projects/activeprojects

Unlike WCF REST service where you need to attribute your method to return the result in a specific format (WebMessageFormat), Web APIs allow the client to specify the format they accept, and Web API will format it accordingly. This is achieved by the client specifying the format in the Accept header in the HTTP request. For an example, if you want the data returned as XML, you would set the Accept header in Fiddler like this Accept : application/xml.

Another cool thing about Web APis, is that it allows OData like syntax to query the API it self for an example, if I want to get only the top 2 projects...my URL would be like this

http://localhost:51499/api/projects/activeprojects?$top=2

However, this to work, you need change your return type IQueryable like this...

public IQueryable<Project> ActiveProjects()

{

return GetProjectsFromDB(true).AsQueryable();

}

The URL format for your return the top 2 projects ordering it by ProjectType would be like this..

http://localhost:51499/api/projects/activeprojects?$top=2&$orderby=ProjectType

Web APIs can be self hosted in a console application and also be written in ASP.net web forms

Thats all i have time for today...

Friday, March 30, 2012

Simple factory, Dependency Injection and Unity

Someone asked me the question whether a simple factory can be implemented using dependency injection container. The example he bought up is where a simple factory takes in a string and switches this string to return the correct instance of the object needed....I am talking about something like this.

internal IWaterMarkProvider GetProvider(string fileExtension)

{

IWaterMarkProvider provider = null;

switch (fileExtension.ToLower())

{

case "pdf":

provider = new PDFProvider();

break;

case ".docx":

provider = new WordProvider();

break;

case "pptx":

provider = new PPTProvider();

break;

case "xlsx":

provider = new ExcelProvider();

break;

}

return provider;

}

The answer was yes..So, if you are using Microsoft Unity (a dependency injection container), you would have your configuration file like this...

<configuration>

<configSections>

<section name="unity" type="Microsoft.Practices.Unity.Configuration.UnityConfigurationSection, Microsoft.Practices.Unity.Configuration"/>

configSections>

<unity xmlns="http://schemas.microsoft.com/practices/2010/unity">

<container name="providerContainer">

<register type="TestLibrary.IWaterMarkProvider,TestLibrary" name="docx" mapTo="TestLibrary.WordProvider,TestLibrary" />

<register type="TestLibrary.IWaterMarkProvider,TestLibrary" name="pdf" mapTo="TestLibrary.PDFProvider,TestLibrary" />

<register type="TestLibrary.IWaterMarkProvider,TestLibrary" name="pptx" mapTo="TestLibrary.PPTProvider,TestLibrary" />

<register type="TestLibrary.IWaterMarkProvider,TestLibrary" name="xlsx" mapTo="TestLibrary.ExcelProvider,TestLibrary" />

<container>

<unity>

<configuration>

We are basically configuring a Unity container and configuring "named" registrations for the IWaterMarkProvider interface. So for an example, the named registration "docx" is mapped to the WordProvider. Hence when we resolve an instance for the IWaterMarkProvider passing the file extension "docx", the Unity container will create an instance of the WordProvider class.
The code below shows how to do this....

IUnityContainer container = new UnityContainer().LoadConfiguration("providerContainer");

IWaterMarkProvider provider = container.Resolve<IWaterMarkProvider>(fileType);

provider.WaterMark();


Note that "providerContainer" is the name of the container specified in the configuration file.
The "fileType" is a parameter that holds the type of the file e.g. "docx"
Whats the advantage of this approach to the approach that we initial put forward, that is with the simple factory we implemened in the first code listing?
First, the code for creation of these classes are "outsourced" and responbility of the container
Secondly, the providers can be changed without recompiling the source, this is even true when we add a new file type. We can just configure it on the configuration file.
Thirdly, If these providers depend on other types, the container will take care of injecting these types into the provider.
Another advantage (unreleated to this example) of using Unity, is that it promotes loose coupling. This becomes really easy when mocking while unit testing. As you can just point Unity to your mocks rather then the real dependencies.

Also note that the lifetime of the instances created through the container can be controlled. By default, each call to the container will create a new instance, if you want to have the WordProvider be a singleton, you can do this...

<register type="TestLibrary.IWaterMarkProvider,TestLibrary" name="docx" mapTo="TestLibrary.WordProvider,TestLibrary" >

<lifetime type="singleton"/>

register>

Wednesday, March 28, 2012

System.Runtime.Caching (.Net 4.0)

.Net 4.0 introduced the System.Runtime.Caching namespace, this made developers to make use of caching functionality independent of the cache found in the System.Web DLL.
Caching using the System.Runtime.Caching provides an in memory cache but also allows developers to extend this with a different provider. For an example, you could have an implementation that could hold the items in memory but also persists it into the hard disk for the fear of cache eviction.

Adding an item into the cache is done this way...

//Get the default cache
MemoryCache cache = MemoryCache.Default;

//Add the item

cache.Add("MyKey",

"Nairooz Nilafdeen",

DateTimeOffset.Now.AddMinutes(19));

//Get the item from the cache

if (cache.Contains("MyKey"))

{

Console.WriteLine(cache.Get("MyKey"));

}


The caching namespace also allows you to set ChangeMonitors for the cache policy, for an example, you can specify that the cache needs to expire once a file changes or the database query changes..
You can watch for a file and expire the cache after a specified time period (absolute or sliding) or when the file content changes...the code below demonstrates this.

string fileName = @"C:\ERR_LOG.log";

CacheItemPolicy policy = new CacheItemPolicy();

policy.AbsoluteExpiration = DateTimeOffset.Now.AddSeconds(40);

policy.ChangeMonitors.Add(new HostFileChangeMonitor

(new List<string> {fileName }));


cache.Add("FileKey", "Nairooz Nilafdeen", policy);


You can also attach a SqlDependency with the SqlChangeMonitor to expire the cache when a the result of a watched query changes...

SqlDependency dependency = new SqlDependency();

//initialize sql dependency heree...

policy.ChangeMonitors.Add(new SqlChangeMonitor(dependency));

System.Json, .NET 4.5 and Dynamics

If you have used libraries like Json.Net or the DataContractSerializer or the JavaScriptSerializer, you already know that you would need a strong typed object for you to convert you class hiarachy into JSON. In a few cases this is frustrating.

In one of my earlier posts I talked about DynamicJson, this was an open source library (under MS-PL license) for you to create JSON counterparts from dynamic objects.

DynamicJson allows you to create JSON values from dynamic object, meaning you don’t really need to create a strong typed object, but create your JSON representation on the fly. >net 4.5 comes with a new namespace System.JSON, that exposes similar functionalities. You can try this out by installing System.Json from NuGet. It works seamlessly as .Net 4.5 is just a replacement for .NET 4.0.

So using System.Json, I can create JSON string like this…

dynamic book = new JsonObject();

book.BookName = "Asp.NET MVC";

book.Price = 123.45;

dynamic author = new JsonObject();

author.Name = "JKey Hay";

author.Age = 29;

book.Author = author;

A .ToString() on the book object would reveal the string…

{"BookName":"Asp.NET MVC","Price":123.45,"Author":{"Name":"JKey Hay","Age":29}}

On the other end, you can create a dynamic object from a JSON string like this…

dynamic parsedBook = JsonValue.Parse(str);

Console.WriteLine(parsedBook.BookName);