ASP.NET interview questions, part 1

Explain the differences between Server-side and Client-side code?
Server side scripting means that all the script will be executed by the server and
interpreted as needed. ASP doesn t have some of the functionality like sockets,
uploading, etc. For these you have to make a custom components usually in VB
or VC++. Client side scripting means that the script will be executed immediately
in the browser such as form field validation, clock, email validation, etc. Client
side scripting is usually done in VBScript or JavaScript. Download time, browser
compatibility, and visible code - since JavaScript and VBScript code is included
in the HTML page, then anyone can see the code by viewing the page source.
Also a possible security hazards for the client computer.
What type of code (server or client) is found in a Code-Behind class?
C#
Should validation (did the user enter a real date) occur server-side or clientside?
Why?
Client-side validation because there is no need to request a server side date when
you could obtain a date from the client machine.
What does the "EnableViewState" property do? Why would I want it on or off?
Enable ViewState turns on the automatic state management feature that enables
server controls to re-populate their values on a round trip without requiring you to
write any code. This feature is not free however, since the state of a control is

passed to and from the server in a hidden form field. You should be aware of
when ViewState is helping you and when it is not. For example, if you are
binding a control to data on every round trip (as in the datagrid example in tip
#4), then you do not need the control to maintain it s view state, since you will
wipe out any re-populated data in any case. ViewState is enabled for all server
controls by default. To disable it, set the EnableViewState property of the control
to false.
What is the difference between Server.Transfer and Response.Redirect? Why
would I choose one over the other?
Server.Transfer() : client is shown as it is on the requesting page only, but the all
the content is of the requested page. Data can be persist accros the pages using
Context.Item collection, which is one of the best way to transfer data from one
page to another keeping the page state alive. Response.Dedirect() :client know the
physical loation (page name and query string as well). Context.Items loses the
persisitance when nevigate to destination page. In earlier versions of IIS, if we
wanted to send a user to a new Web page, the only option we had was
Response.Redirect. While this method does accomplish our goal, it has several
important drawbacks. The biggest problem is that this method causes each page to
be treated as a separate transaction. Besides making it difficult to maintain your
transactional integrity, Response.Redirect introduces some additional headaches.
First, it prevents good encapsulation of code. Second, you lose access to all of the
properties in the Request object. Sure, there are workarounds, but they re
difficult. Finally, Response.Redirect necessitates a round trip to the client, which,
on high-volume sites, causes scalability problems. As you might suspect,
Server.Transfer fixes all of these problems. It does this by performing the transfer
on the server without requiring a roundtrip to the client.
Can you give an example of when it would be appropriate to use a web service as
opposed to a non-serviced .NET component?
When to Use Web Services:
Communicating through a Firewall When building a distributed application
with 100s/1000s of users spread over multiple locations, there is always
the problem of communicating between client and server because of
firewalls and proxy servers. Exposing your middle tier components as
Web Services and invoking the directly from a Windows UI is a very valid
option.
Application Integration When integrating applications written in various
languages and running on disparate systems. Or even applications running
on the same platform that have been written by separate vendors.
Business-to-Business Integration This is an enabler for B2B intergtation
which allows one to expose vital business processes to authorized supplier
and customers. An example would be exposing electronic ordering and
invoicing, allowing customers to send you purchase orders and suppliers
to send you invoices electronically.
Software Reuse This takes place at multiple levels. Code Reuse at the Source
code level or binary componet-based resuse. The limiting factor here is
that you can reuse the code but not the data behind it. Webservice

overcome this limitation. A scenario could be when you are building an
app that aggregates the functionality of serveral other Applicatons. Each
of these functions could be performed by individual apps, but there is
value in perhaps combining the the multiple apps to present a unifiend
view in a Portal or Intranet.
When not to use Web Services: Single machine Applicatons When the apps
are running on the same machine and need to communicate with each
other use a native API. You also have the options of using component
technologies such as COM or .NET Componets as there is very little
overhead.
Homogeneous Applications on a LAN If you have Win32 or Winforms apps
that want to communicate to their server counterpart. It is much more
efficient to use DCOM in the case of Win32 apps and .NET Remoting in
the case of .NET Apps.
Let s say I have an existing application written using Visual Studio
(VBInterDev and this application utilizes Windows COM+ transaction
services. How would you approach migrating this application to .NET?
Can you explain the difference between an ADO.NET Dataset and an ADO
Recordset?
In ADO, the in-memory representation of data is the recordset. In ADO.NET, it
is the dataset. There are important differences between them.
A recordset looks like a single table. If a recordset is to contain data from
multiple database tables, it must use a JOIN query, which assembles the
data from the various database tables into a single result table. In contrast,
a dataset is a collection of one or more tables. The tables within a dataset
are called data tables; specifically, they are DataTable objects. If a dataset
contains data from multiple database tables, it will typically contain
multiple DataTable objects. That is, each DataTable object typically
corresponds to a single database table or view. In this way, a dataset can
mimic the structure of the underlying database. A dataset usually also
contains relationships. A relationship within a dataset is analogous to a
foreign-key relationship in a database -that is, it associates rows of the
tables with each other. For example, if a dataset contains a table about
investors and another table about each investor s stock purchases, it could
also contain a relationship connecting each row of the investor table with
the corresponding rows of the purchase table. Because the dataset can hold
multiple, separate tables and maintain information about relationships
between them, it can hold much richer data structures than a recordset,
including self-relating tables and tables with many-to-many relationships.
In ADO you scan sequentially through the rows of the recordset using the
ADO MoveNext method. In ADO.NET, rows are represented as
collections, so you can loop through a table as you would through any
collection, or access particular rows via ordinal or primary key index.
DataRelation objects maintain information about master and detail records

and provide a method that allows you to get records related to the one you
are working with. For example, starting from the row of the Investor table
for "Nate Sun," you can navigate to the set of rows of the Purchase table
describing his purchases. A cursor is a database element that controls
record navigation, the ability to update data, and the visibility of changes
made to the database by other users. ADO.NET does not have an inherent
cursor object, but instead includes data classes that provide the
functionality of a traditional cursor. For example, the functionality of a
forward-only, read-only cursor is available in the ADO.NET DataReader
object. For more information about cursor functionality, see Data Access
Technologies.
Minimized Open Connections: In ADO.NET you open connections only long
enough to perform a database operation, such as a Select or Update. You
can read rows into a dataset and then work with them without staying
connected to the data source. In ADO the recordset can provide
disconnected access, but ADO is designed primarily for connected access.
There is one significant difference between disconnected processing in
ADO and ADO.NET. In ADO you communicate with the database by
making calls to an OLE DB provider. In ADO.NET you communicate
with the database through a data adapter (an OleDbDataAdapter,
SqlDataAdapter, OdbcDataAdapter, or OracleDataAdapter object), which
makes calls to an OLE DB provider or the APIs provided by the
underlying data source. The important difference is that in ADO.NET the
data adapter allows you to control how the changes to the dataset are
transmitted to the database - by optimizing for performance, performing
data validation checks, or adding any other extra processing. Data
adapters, data connections, data commands, and data readers are the
components that make up a .NET Framework data provider. Microsoft and
third-party providers can make available other .NET Framework data
providers that can be integrated into Visual Studio.
Sharing Data Between Applications. Transmitting an ADO.NET dataset
between applications is much easier than transmitting an ADO
disconnected recordset. To transmit an ADO disconnected recordset from
one component to another, you use COM marshalling. To transmit data in
ADO.NET, you use a dataset, which can transmit an XML stream.
Richer data types.COM marshalling provides a limited set of data types -
those defined by the COM standard. Because the transmission of datasets
in ADO.NET is based on an XML format, there is no restriction on data
types. Thus, the components sharing the dataset can use whatever rich set
of data types they would ordinarily use.
Performance. Transmitting a large ADO recordset or a large ADO.NET
dataset can consume network resources; as the amount of data grows, the

stress placed on the network also rises. Both ADO and ADO.NET let you
minimize which data is transmitted. But ADO.NET offers another
performance advantage, in that ADO.NET does not require data-type
conversions. ADO, which requires COM marshalling to transmit records
sets among components, does require that ADO data types be converted to
COM data types.
Penetrating Firewalls.A firewall can interfere with two components trying to
transmit disconnected ADO recordsets. Remember, firewalls are typically
configured to allow HTML text to pass, but to prevent system-level
requests (such as COM marshalling) from passing.
Can you give an example of what might be best suited to place in the
Application_Start and Session_Start subroutines?
The Application_Start event is guaranteed to occur only once throughout the
lifetime of the application. It s a good place to initialize global variables. For
example, you might want to retrieve a list of products from a database table and
place the list in application state or the Cache object. SessionStateModule
exposes both Session_Start and Session_End events.
If I m developing an application that must accomodate multiple security levels
though secure login and my ASP.NET web appplication is spanned across
three web-servers (using round-robbin load balancing) what would be the
best approach to maintain login-in state for the users?
What are ASP.NET Web Forms? How is this technology different than what is
available though ASP?
Web Forms are the heart and soul of ASP.NET
Web Forms are the User Interface
(UI) elements that give your Web applications their look and feel. Web Forms are
similar to Windows Forms in that they provide properties, methods, and events
for the controls that are placed onto them. However, these UI elements render
themselves in the appropriate markup language required by the request, e.g.
HTML. If you use Microsoft Visual Studio .NET, you will also get the familiar
drag-and-drop interface used to create your UI for your Web application.
How does VB.NET/C# achieve polymorphism?
By using Abstract classes/functions.
Can you explain what inheritance is and an example of when you might use it?
Inheritance is a fundamental feature of an object oriented system and it is simply the
ability to inherit data and functionality from a parent object. Rather than
developing new objects from scratch, new code can be based on the work of other
programmers, adding only new features that are needed.
How would you implement inheritance using VB.NET/C#?
When we set out to implement a class using inheritance, we must first start with
an existing class from which we will derive our new subclass. This existing class,
or base class, may be part of the .NET system class library framework, it may be
part of some other application or .NET assembly, or we may create it as part of
our existing application. Once we have a base class, we can then implement one

or more subclasses based on that base class. Each of our subclasses will
automatically have all of the methods, properties, and events of that base class ?
including the implementation behind each method, property, and event. Our
subclass can add new methods, properties, and events of its own - extending the
original interface with new functionality. Additionally, a subclass can replace the
methods and properties of the base class with its own new implementation -
effectively overriding the original behavior and replacing it with new behaviors.
Essentially inheritance is a way of merging functionality from an existing class
into our new subclass. Inheritance also defines rules for how these methods,
properties, and events can be merged.