Wednesday, 21 November 2012

MVC (Model View Controller) Interview Questions



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

1- In which assembly is the MVC framework defined?
System.Web.Mvc

2- Is it possible to combine ASP.NET web forms and ASP.MVC and develop a single web application?
Yes, it is possible to combine ASP.NET web forms and ASP.MVC and develop a single web application.

3- 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 within the model.
View: Views represent the user interface, with which the end users interact. In short the all the user interface logic is contained within 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 within the controller.

4- What is the greatest advantage of using asp.net MVC over asp.net web forms?
It is difficult to unit test UI with web forms, 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 Web forms?
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 syntaxes to include server side code in to HTML.

7- What are the 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 view state.

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 also 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, which 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 advantages 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 web forms application and to an MVC application?
To add routes to a webforms application, we use MapPageRoute() method of the RouteCollection class, whereas 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?
<%= %>

42- When using razor views, do you have to take any special steps to proctect 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- In razor syntax, what is the escape sequence character for @ symbol?
The escape sequence character for @ symbol, is another @ symbol.


49 - How do you avoid XSS Vulnerabilities in ASP.NET MVC?
Use the syntax in ASP.NET MVC instead of using in .net framework 4.0.


Monday, 19 November 2012

MVC Data Annotations for Model Validation


What are data annotations?

Data annotations are attribute classes that live in the System.ComponentModel.DataAnnotations namespace that you can use to apply to (decorate) classes or properties to enforce pre-defined validation rules.

Data Annotations help us to define the rules to the model classes or properties for data validation and displaying suitable messages to end users.

Data Annotation Validator Attributes:

1. DataType: Specify the datatype of a property
2. DisplayName: Specify the display name for a property.
3. DisplayFormat:  Specify the display format for a property like different format for Date proerty.
4. Required: Specify a property as required.
5. ReqularExpression: Validate the value of a property by specified regular expression pattern.
6. Range: Validate the value of a property within a specified range of values.
7. StringLength: Specify min and max length for a string property.
8. MaxLength: Specify max length for a string property.
9. Bind: Specify fields to include or exclude when adding parameter or form values to model properties.
10. ScaffoldColumn: Specify fields for hiding from editor forms.

Designing the model with Data Annotations:

using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Web.Mvc;

namespace Employee.Models
{
    [Bind(Exclude = "AlbumId")]
    public class Employee
    {
        [ScaffoldColumn(false)]
        public int EmpId { get; set; }

        [DisplayName("Employee Name")]
        [Required(ErrorMessage = "Employee Name is required")]
        [StringLength(100, MinimumLength = 3)]
        public String EmpName { get; set; }

        [Required(ErrorMessage = "Employee Address is required")]
        [StringLength(300)]
        public string Address { get; set; }

        [Required(ErrorMessage = "Salary is required")]
        [Range(3000, 10000000, ErrorMessage = "Salary must be between 3000 and 10000000")]
        public int Salary { get; set; }

        [Required(ErrorMessage = "Please enter your email address")]
        [DataType(DataType.EmailAddress)]
        [Display(Name = "Email address")]
        [MaxLength(50)]
        [RegularExpression(@"[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,4}", ErrorMessage = "Please enter correct email")]
        public string Email { get; set; }
    }
}

Once we have defined validation to the model by using data annotations, these are automatically used by Html Helpers in views. For client side validation to work, please ensure that below two <SCRIPT> tag references are in the view.
<script src="@Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript"></script>
<script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"></script>


Presenting the model in the view:

@model Employee.Models
@{
    ViewBag.Title = "Employee Details";
    Layout = "~/Views/Shared/_Layout.cshtml";
}
@using (Html.BeginForm())
{
    <div class="editor-label">
        @Html.LabelFor(m => m.EmpName)
    </div>
   
    <div class="editor-field">
        @Html.TextBoxFor(m => m.EmpName) @Html.ValidationMessageFor(m => m.EmpName)
    </div>
   
    <div class="editor-label">
        @Html.LabelFor(m => m.Address)
    </div>
   
    <div class="editor-field">
        @Html.TextBoxFor(m => m.Address) @Html.ValidationMessageFor(m => m.Address)
    </div>
   
    <div class="editor-label">
        @Html.LabelFor(m => m.Salary)
    </div>
   
    <div class="editor-field">
        @Html.TextBoxFor(m => m.Salary) @Html.ValidationMessageFor(m => m.Salary)
    </div>
   
    <div class="editor-label">
        @Html.LabelFor(m => m.Email)
    </div>
   
    <div class="editor-field">
        @Html.TextBoxFor(m => m.Email) @Html.ValidationMessageFor(m => m.Email)
    </div>
   
    <p>
        <input type="submit" value="Save" />
    </p>
}