DOT NET LATEST - 1

What is LINQ?

It stands for Language Integrated Query. LINQ is collection of standard query operators that provides the query facilities into .NET framework language like C# , VB.NET.

Why Select clause comes after from clause in LINQ?

The reason is, LINQ is used with C# or other programming languages, which requires all the variables to be declared first. From clause of LINQ query just defines the range or conditions to select records. So that’s why from clause must appear before Select in LINQ.

How LINQ is beneficial than Stored Procedures?

There are couple of advantage of LINQ over stored procedures.

1. Debugging - It is really very hard to debug the Stored procedure but as LINQ is part of .NET, you can use visual studio's debugger to debug the queries.

2. Deployment - With stored procedures, we need to provide an additional script for stored procedures but with LINQ everything gets complied into single DLL hence deployment becomes easy.

3. Type Safety - LINQ is type safe, so queries errors are type checked at compile time. It is really good to encounter an error when compiling rather than runtime exception!

What is a Lambda expression?

A Lambda expression is nothing but an Anonymous Function, can contain expressions and statements. Lambda expressions can be used mostly to create delegates or expression tree types. Lambda expression uses lambda operator => and read as 'goes to' operator.

Left side of this operator specifies the input parameters and contains the expression or statement block at the right side.

Example: myExp = myExp/10;

Now, let see how we can assign the above to a delegate and create an expression tree:

delegate int myDel(int intMyNum);
static void Main(string[] args)
{
//assign lambda expression to a delegate:
myDel myDelegate = myExp => myExp / 10;
int intRes = myDelegate(110);
Console.WriteLine("Output {0}", intRes);
Console.ReadLine();

//Create an expression tree type
//This needs System.Linq.Expressions
Expression myExpDel = myExp => myExp /10;

}

No te:
The => operator has the same precedence as assignment (=) and is right-associative.

Lambdas are used in method-based LINQ queries as arguments to standard query operator methods such as Where

ViewData

1. ViewData is a dictionary object that is derived from ViewDataDictionary class.
2. ViewData is used to pass data from controller to corresponding view.
3. It’s life lies only during the current request.
4. If redirection occurs then it’s value becomes null.
5. It’s required typecasting for complex data type and check for null values to avoid error.

ViewBag

1. ViewBag is a dynamic property that takes advantage of the new dynamic features in C# 4.0.
2. Basically it is a wrapper around the ViewData and also used to pass data from controller to corresponding view.
3. It’s life also lies only during the current request.
4. If redirection occurs then it’s value becomes null.
5. It doesn’t required typecasting for complex data type.

TempData

1. TempData is a dictionary object that is derived from TempDataDictionary class and stored in short lives session.
2. TempData is used to pass data from current request to subsequent request means incase of redirection.
3. It’s life is very short and lies only till the target view is fully loaded.
4. It’s required typecasting for complex data type and check for null values to avoid error.
5. It is used to store only one time messages like error messages, validation messages.

ViewData, ViewBag and TempData Current Request Example

 public class HomeController : Controller
{
 public ActionResult Index()
 {
 var emp = new Employee
 {
 EmpID=101,
 Name = "Deepak",
 Salary = 35000,
 Address = "Delhi"
 }; 
 ViewData["emp"] = emp;
 ViewBag.Employee = emp;
 TempData["emp"] = emp; 
 return View(); }
} 

WCF Rest

1. To use WCF as WCF Rest service you have to enable webHttpBindings.
2. It support HTTP GET and POST verbs by [WebGet] and [WebInvoke] attributes respectively.
3. To enable other HTTP verbs you have to do some configuration in IIS to accept request of that particular verb on .svc files
4. Passing data through parameters using a WebGet needs configuration. The UriTemplate must be specified
5. It support XML, JSON and ATOM data format.

Web API

1. This is the new framework for building HTTP services with easy and simple way.
2. Web API is open source an ideal platform for building REST-ful services over the .NET Framework.
3. Unlike WCF Rest service, it use the full featues of HTTP (like URIs, request/response headers, caching, versioning, various content formats)
4. It also supports the MVC features such as routing, controllers, action results, filter, model binders, IOC container or dependency injection, unit testing that makes it more simple and robust.
5. It can be hosted with in the application or on IIS.
6. It is light weight architecture and good for devices which have limited bandwidth like smart phones.
7. Responses are formatted by Web API’s MediaTypeFormatter into JSON, XML or whatever format you want to add as a MediaTypeFormatter.

To whom choose between WCF or WEB API

1. Choose WCF when you want to create a service that should support special scenarios such as one way messaging, message queues, duplex communication etc.
2. Choose WCF when you want to create a service that can use fast transport channels when available, such as TCP, Named Pipes, or maybe even UDP (in WCF 4.5), and you also want to support HTTP when all other transport channels are unavailable.
3. Choose Web API when you want to create a resource-oriented services over HTTP that can use the full features of HTTP (like URIs, request/response headers, caching, versioning, various content formats).
4. Choose Web API when you want to expose your service to a broad range of clients including browsers, mobiles, iphone and tablets.

RESTful service

 

RESTful services are those which follow the REST (Representational State Transfer) architectural style.
Before implementing your first RESTful service, lets first understand the concept behind it. As we know that WCF allows us to make calls and exchange messages using SOAP over a variety of protocols i.e. HTTP, TCP, Named Pipes and MSMQ etc. In a scenario, if we are using SOAP over HTTP, we are just utilizing HTTP as a transport. But HTTP is much more than just a transport. So, when we talk about REST architectural style, it dictates that “Instead of using complex mechanisms like CORBA, RPC or SOAP for communication, simply HTTP should be used for making calls”.
RESTful architecture use HTTP for all CRUD operations like (Read/Create/Update/Delete) using simple HTTP verbs like (GET, POST, PUT, and DELETE). It’s simple as well as lightweight. For the sake of simplicity, I am going to implement only a GET request for which service will return certain types of data (i.e. Product data) in XML format

Action Filters

There are a set of Action filters available with ASP.NET MVC 3 to filter actions. Action filters are defined as attributes and applied to an Action or controller.

1. Authorize

Authorize filters ensure that the corresponding Action will be called by an authorized user only. If the user is not authorized, he will be redirected to the login page.

[Authorize]
public ActionResult About()
{
    return View();
}

If the user is not authorized and invoke the About action, then he will redirected to the log on page.

2. HandleError

HandleError will handle the various exceptions thrown by the application and display user friendly message to the user. By default, this filter is registered in Global.asax.
Note: If any of the Action filters are added to the filter collection in Global.asax, then the scope of the filter is the application.

public static void RegisterGlobalFilters(GlobalFilterCollection filters)
{
    filters.Add(new HandleErrorAttribute());
}

For verifying a filter, let us enable a custom error in web.config:

Action Selectors ASP.NET MVC 3 defines a set of Action selectors which determine the selection of an Action. One of them is ActionName, used for defining an alias for an Action. When we define an alias for an Action, the Action will be invoked using only the alias; not with the Action name. [ActionName("NewAbout")] public ActionResult About() { return Content("Hello from New About"); }

Filter Types

• Authorization filters. These implement IAuthorizationFilter and make security decisions about whether to execute an action method, such as performing authentication or validating properties of the request. The AuthorizeAttribute class and the RequireHttpsAttribute class are examples of an authorization filter. Authorization filters run before any other filter.
• Action filters. These implement IActionFilter and wrap the action method execution. The IActionFilter interface declares two methods: OnActionExecuting and OnActionExecuted. OnActionExecuting runs before the action method. OnActionExecuted runs after the action method and can perform additional processing, such as providing extra data to the action method, inspecting the return value, or canceling execution of the action method.
• Result filters. These implement IResultFilter and wrap execution of the ActionResult object. IResultFilter declares two methods: OnResultExecuting and OnResultExecuted. OnResultExecuting runs before the ActionResult object is executed. OnResultExecuted runs after the result and can perform additional processing of the result, such as modifying the HTTP response. The OutputCacheAttribute class is one example of a result filter.
• Exception filters. These implement IExceptionFilter and execute if there is an unhandled exception thrown during the execution of the ASP.NET MVC pipeline. Exception filters can be used for tasks such as logging or displaying an error page. The HandleErrorAttribute class is one example of an exception filter.

Asynchronous Controller

The AsyncController class enables you to write asynchronous action methods. You can use asynchronous action methods for long-running, non-CPU bound requests. This avoids blocking the Web server from performing work while the request is being processed. A typical use for the AsyncController class is long-running Web service calls.

The asynchronous controller enables you to write asynchronous action methods. It allows you to perform long running operation(s) without making the running thread idle. It does not mean it will take lesser time to complete the action. If a request make a service call that require two seconds to complete it, the request will take two seconds whether it is performed synchronously or asynchronously. However, during asynchronous call, the server is not blocked from responding to the other requests.

 Asynchronous Controller

Asynchronous action methods are useful when an action must perform several independent long running operations. Suppose we have three operations which takes 500, 600 and 700 milliseconds. With the synchronous call, total response time would be slightly more than 1800 milliseconds. However, if the calls are made asynchronously (in parallel), total response time would be slightly more than 700 milliseconds, because that is the duration of longest task/operation.

How to create Asynchronous Controller

1. Inherits MVC controller with AsyncController instead of Controller.
2. Asynchronous action methods are useful when an action must perform several independent long running operations. Suppose we have three operations which takes 500, 600 and 700 milliseconds. With the synchronous call, total response time would be slightly more than 1800 milliseconds. However, if the calls are made asynchronously (in parallel), total response time would be slightly more than 700 milliseconds, because that is the duration of longest task/operation.

public class AsynchronuosTestingController : AsyncController
{
    private readonly object _lock = new object();
    public void IndexAsync()
    {
        AsyncManager.OutstandingOperations.Increment(2);
        Operation1();
        Operation2();
    }
    public ActionResult IndexCompleted(string Operation1, string Operation2)
    {
        ViewData["Operation1"] = Operation1;
        ViewData["Operation2"] = Operation2;
        return View("Index");
    }
    void Operation1()
    {
        lock (_lock)
        {
            AsyncManager.Parameters["Operation1"] = "Result1";
        }
        //last line of this method
    
        AsyncManager.OutstandingOperations.Decrement();
    }
    void Operation2()
    {
        lock (_lock)
        {
            AsyncManager.Parameters["Operation2"] = "Result2";
        }
        //last line of this method
    
        AsyncManager.OutstandingOperations.Decrement();
    }
}

1. What is MVC?

MVC is a framework methodology that divides an application’s implementation into three component roles: models, views, and controllers.

Main components of an MVC application?

1. M - Model

2. V - View

3. C - Controller

“Models” in a MVC based application are the components of the application that are responsible for maintaining state. Often this state is persisted inside a database (for example: we might have a Product class that is used to represent order data from the Products table inside SQL).

“Views” in a MVC based application are the components responsible for displaying the application’s user interface. Typically this UI is created off of the model data (for example: we might create an Product “Edit” view that surfaces textboxes, dropdowns and checkboxes based on the current state of a Product object).

“Controllers” in a MVC based application are the components responsible for handling end user interaction, manipulating the model, and ultimately choosing a view to render to display UI. In a MVC application the view is only about displaying information – it is the controller that handles and responds to user input and interaction.

2- What does Model, View and Controller represent in an MVC application?

Model: Model represents the application data domain. In short the applications business logic is contained with in the model.

View: Views represent the user interface, with which the end users interact. In short the all the user interface logic is contained with in the UI.

Controller: Controller is the component that responds to user actions. Based on the user actions, the respective controller, work with the model, and selects a view to render that displays the user interface. The user input logic is contained with in the controller.

3- In which assembly is the MVC framework defined?

System.Web.Mvc

4- What is the greatest advantage of using asp.net mvc over asp.net webforms?

It is difficult to unit test UI with webforms, where views in mvc can be very easily unit tested.

5- Which approach provides better support for test driven development - ASP.NET MVC or ASP.NET Webforms?

ASP.NET MVC

6- What is Razor View Engine?

Razor view engine is a new view engine created with ASP.Net MVC model using specially designed Razor parser to render the HTML out of dynamic server side code. It allows us to write Compact, Expressive, Clean and Fluid code with new syntax to include server side code in to HTML.

7- What are the advantages of ASP.NET MVC?

Advantages of ASP.NET MVC:

1. Extensive support for TDD. With asp.net MVC, views can also be very easily unit tested.

2. Complex applications can be easily managed

3. Separation of concerns. Different aspects of the application can be divided into Model, View and Controller.

4. ASP.NET MVC views are light weight, as they don't use viewstate.

8- Is it possible to unit test an MVC application without running the controllers in an ASP.NET process?

Yes, all the features in an asp.net MVC application are interface based and hence mocking is much easier. So, we don't have to run the controllers in an ASP.NET process for unit testing.

9- What is namespace of ASP.NET MVC?

ASP.NET MVC namespaces and classes are located in the System.Web.Mvc assembly.

System.Web.Mvc namespace 

Contains classes and interfaces that support the MVC pattern for ASP.NET Web applications. This namespace includes classes that represent controllers, controller factories, action results, views, partial views, and model binders.

System.Web.Mvc.Ajax namespace 

Contains classes that support Ajax scripts in an ASP.NET MVC application. The namespace includes support for Ajax scripts and Ajax option settings.

System.Web.Mvc.Async namespace 

Contains classes and interfaces that support asynchronous actions in an ASP.NET MVC application.

System.Web.Mvc.Html namespace 

Contains classes that help render HTML controls in an MVC application. The namespace includes classes that support forms, input controls, links, partial views, and validation.

10- Is it possible to share a view across multiple controllers?

Yes, put the view into the shared folder. This will automatically make the view available across multiple controllers.

11- What is the role of a controller in an MVC application?

The controller responds to user interactions, with the application, by selecting the action method to execute and selecting the view to render.

12- Where are the routing rules defined in an asp.net MVC application?

In Application_Start event in Global.asax

13- Name a few different return types of a controller action method?

The following are just a few return types of a controller action method. In general an action method can return an instance of a any class that derives from ActionResult class.

1. ViewResult

2. JavaScriptResult

3. RedirectResult

4. ContentResult

5. JsonResult

14- What is the ‘page lifecycle’ of an ASP.NET MVC?

Following process are performed by ASP.Net MVC page:

1) App initialization

2) Routing

3) Instantiate and execute controller

4) Locate and invoke controller action

5) Instantiate and render view

15- What is the significance of NonActionAttribute?

In general, all public methods of a controller class are treated as action methods. If you want prevent this default behavior, just decorate the public method with NonActionAttribute.

16- What is the significance of ASP.NET routing?

ASP.NET MVC uses ASP.NET routing, to map incoming browser requests to controller action methods. ASP.NET Routing makes use of route table. Route table is created when your web application first starts. The route table is present in the Global.asax file.

17- How route table is created in ASP.NET MVC?

When an MVC application first starts, the Application_Start() method is called. This method, in turn, calls the RegisterRoutes() method. The RegisterRoutes() method creates the route table.

18- What are the 3 segments of the default route, that is present in an ASP.NET MVC application?

1st Segment - Controller Name

2nd Segment - Action Method Name

3rd Segment - Parameter that is passed to the action method

Example: http://google.com/search/label/MVC

Controller Name = search

Action Method Name = label

Parameter Id = MVC

19- ASP.NET MVC application, makes use of settings at 2 places for routing to work correctly. What are these 2 places?

1. Web.Config File : ASP.NET routing has to be enabled here.

2. Global.asax File : The Route table is created in the application Start event handler, of the Global.asax file.

20- What is the adavantage of using ASP.NET routing?

In an ASP.NET web application that does not make use of routing, an incoming browser request should map to a physical file. If the file does not exist, we get page not found error.

An ASP.NET web application that does make use of routing, makes use of URLs that do not have to map to specific files in a Web site. Because the URL does not have to map to a file, you can use URLs that are descriptive of the user's action and therefore are more easily understood by users.

21- What are the 3 things that are needed to specify a route?

1. URL Pattern - You can include placeholders in a URL pattern so that variable data can be passed to the request handler without requiring a query string.

2. Handler - The handler can be a physical file such as an .aspx file or a controller class.

3. Name for the Route - Name is optional.

22- Is the following route definition a valid route definition?

{controller}{action}/{id}

No, the above definition is not a valid route definition, because there is no literal value or delimiter between the placeholders. Therefore, routing cannot determine where to separate the value for the controller placeholder from the value for the action placeholder.

23- What is the use of the following default route?

{resource}.axd/{*pathInfo}

This route definition, prevent requests for the Web resource files such as WebResource.axd or ScriptResource.axd from being passed to a controller.

24- What is the difference between adding routes, to a webforms application and to an mvc application?

To add routes to a webforms application, we use MapPageRoute() method of the RouteCollection class, where as to add routes to an MVC application we use MapRoute() method.

25- How do you handle variable number of segments in a route definition?

Use a route with a catch-all parameter. An example is shown below. * is referred to as catch-all parameter.

controller/{action}/{*parametervalues}

26- What are the 2 ways of adding constraints to a route?

1. Use regular expressions

2. Use an object that implements IRouteConstraint interface

27- Give 2 examples for scenarios when routing is not applied?

1. A Physical File is Found that Matches the URL Pattern - This default behaviour can be overriden by setting the RouteExistingFiles property of the RouteCollection object to true.

2. Routing Is Explicitly Disabled for a URL Pattern - Use the RouteCollection.Ignore() method to prevent routing from handling certain requests.

28- What is the use of action filters in an MVC application?

Action Filters allow us to add pre-action and post-action behavior to controller action methods.

29- If I have multiple filters implemented, what is the order in which these filters get executed?

1. Authorization filters

2. Action filters

3. Response filters

4. Exception filters

30- What are the different types of filters, in an asp.net mvc application?

1. Authorization filters

2. Action filters

3. Result filters

4. Exception filters

31- Give an example for Authorization filters in an asp.net mvc application?

1. RequireHttpsAttribute

2. AuthorizeAttribute

32- Which filter executes first in an asp.net mvc application?

Authorization filter

33- What are the levels at which filters can be applied in an asp.net mvc application?

1. Action Method

2. Controller

3. Application

34- Is it possible to create a custom filter?

Yes

35- What filters are executed in the end?

Exception Filters

36- Is it possible to cancel filter execution?

Yes

37- What type of filter does OutputCacheAttribute class represents?

Result Filter

38- What are the 2 popular asp.net mvc view engines?

1. Razor

2. .aspx

39- What is difference between Viewbag and Viewdata in ASP.NET MVC?

The basic difference between ViewData and ViewBag is that in ViewData instead creating dynamic properties we use properties of Model to transport the Model data in View and in ViewBag we can create dynamic properties without using Model data.

40- What symbol would you use to denote, the start of a code block in razor views?

@

41- What symbol would you use to denote, the start of a code block in aspx views?

<%= %>

In razor syntax, what is the escape sequence character for @ symbol?

The escape sequence character for @ symbol, is another @ symbol

42- When using razor views, do you have to take any special steps to protect your asp.net mvc application from cross site scripting (XSS) attacks?

No, by default content emitted using a @ block is automatically HTML encoded to protect from cross site scripting (XSS) attacks.

43- When using aspx view engine, to have a consistent look and feel, across all pages of the application, we can make use of asp.net master pages. What is asp.net master pages equivalent, when using razor views?

To have a consistent look and feel when using razor views, we can make use of layout pages. Layout pages, reside in the shared folder, and are named as _Layout.cshtml

44- What are sections?

Layout pages, can define sections, which can then be overriden by specific views making use of the layout. Defining and overriding sections is optional.

45- What are the file extensions for razor views?

1. .cshtml - If the programming lanugaue is C#

2. .vbhtml - If the programming lanugaue is VB

46- How do you specify comments using razor syntax?

Razor syntax makes use of @* to indicate the begining of a comment and *@ to indicate the end. 

47- What is Routing?

A route is a URL pattern that is mapped to a handler. The handler can be a physical file, such as an .aspx file in a Web Forms application. Routing module is responsible for mapping incoming browser requests to particular MVC controller actions.

48- Is it possible to combine ASP.NET webforms and ASP.MVC and develop a single web application?

Yes, it is possible to combine ASP.NET webforms and ASP.MVC and develop a single web application.

49. How do you avoid XSS Vulnerabilities in ASP.NET MVC?

Use the syntax in ASP.NET MVC instead of using .net framework 4.0.