What is ADO .NET and what is
difference between ADO and ADO.NET?
ADO.NET is stateless mechanism. I can treat the ADO.Net as
a separate in-memory database where in I can use relationships between the
tables and select insert and updates to the database. I can update the actual
database as a batch.
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 client-side? 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 across 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 location (page name and query string as well). Context.Items loses
the persistence when navigate 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 integration 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 component-based reuse. 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 several other Applications. Each of
these functions could be performed by individual apps, but there is value in
perhaps combining the multiple apps to present a unified view in a Portal or
Intranet.
* When not to use Web Services: Single machine Applications
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 Components 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.
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.
