Unit 3 & 4

ADO.NET (ActiveX Data Objects .NET) is a data access technology in the .NET Framework used to connect applications with databases, execute queries, and retrieve or manipulate data. It supports both connected and disconnected data access modes.

Features

• 01Supports connected and disconnected data access.
• 02Works with databases such as SQL Server, Oracle, MySQL, and Access.
• 03Supports XML natively through DataSet.
• 04Provides classes for database connection, commands, reading, and updating data.
• 05Uses namespaces such as System.Data and System.Data.SqlClient.

CommandBuilder is an ADO.NET class used to automatically generate the SQL INSERT, UPDATE, and DELETE commands for a DataAdapter. It saves the programmer from writing these commands manually.

Example

SqlCommandBuilder cb = new SqlCommandBuilder(adapter);
adapter.Update(ds);

DataReader is an ADO.NET object used to read data from a database in connected mode. It provides fast, forward-only and read-only access to the result set.

Use

• 01Used mainly for executing SELECT queries and reading records one by one.
• 02The database connection must remain open while the DataReader is being used.
• 03ExecuteReader() is used to obtain a DataReader.

Example

SqlDataReader dr = cmd.ExecuteReader();

while (dr.Read())
{
    string name = dr["Name"].ToString();
}

Client-server communication in ASP.NET is the process in which a web browser (client) sends a request to the ASP.NET server, and the server processes it and sends a response back.

Working

Browser (Client)
      ↓ HTTP Request
ASP.NET Web Server
      ↓
Process Request
      ↓
HTTP Response
      ↓
Browser (Client)

ASP.NET mainly uses two objects:

• RequestReceives data sent by the browser, such as form values, query strings, cookies, and headers.
• ResponseSends data from the server to the browser, such as HTML, redirects, cookies, and files.

A Cookie is a small piece of data stored on the client's browser by the web server. It is used for remembering information such as user preferences, login status, and session tracking.

The Request object is used to read/access cookies sent by the browser. The Response.Cookies collection is used to create or send cookies to the browser.

Example

string name = Request.Cookies["UserName"].Value;

A Query String is data passed through the URL after a ? symbol. It is used to send small amounts of information from the client to the server.

Example

page.aspx?name=Riya&id=1

Here, name and id are query-string parameters.

URL Encoding is the process of converting special characters in a URL into a safe format so that they can be transmitted correctly.

Session State is an ASP.NET state-management technique used to store user-specific data on the server and maintain it between different pages.

Session data is specific to each user.

Example

// Storing a value in session
Session["UserName"] = txtName.Text;

// Retrieving the value
string name = Session["UserName"].ToString();

Application State is an ASP.NET state-management technique used to store data that is shared by all users throughout the entire application.

Example

Application["SiteVisitCount"] = 0;

It can be used for application-wide information such as a total visitor count.

State Management is the technique of maintaining data and information between different requests/pages in an ASP.NET application.

Since HTTP is stateless, ASP.NET provides techniques such as ViewState, Session State, Application State, and Cookies to maintain state.

Web.config is an ASP.NET configuration file used to store and manage application settings and configuration information.

Important Sections

• connectionStringsStores database connection strings used by the ASP.NET application.
• appSettingsStores application-specific settings or key-value pairs.
• sessionStateConfigures Session State, such as session mode and timeout.

Breadcrumb navigation is a navigation technique that shows the current page's location within the website's hierarchy.

Example

Home > Products > Mobiles > Samsung

It helps users understand where they are on the website and easily navigate back to previous pages.

A Web Service is a software component that allows applications to communicate and exchange data over a network.

An ASMX Web Service is a classic ASP.NET Web Service that uses the .asmx file extension. Its public methods are exposed to clients using the [WebMethod] attribute.

The [WebMethod] attribute is applied to a public method in an ASMX Web Service to make that method available as a Web Service operation, so that client applications can invoke it.

Example

[WebMethod]
public int Add(int a, int b)
{
    return a + b;
}

Here, Add() can be called by a client application as a Web Service method.

A Proxy Class is a client-side class generated from the Web Service description (WSDL). It acts as a local representative of the remote Web Service, allowing the client application to call its methods as if they were local methods.

Flow

Web Service → WSDL → Proxy Class → Client Application

The proxy is generated when the client adds a Web Reference/Service Reference to the Web Service.

Consuming a Web Service means using a Web Service from a client application by connecting to the service and calling its available methods.

Basic Process

Web Service
     ↓
   WSDL
     ↓
Proxy Class
     ↓
Client Application
     ↓
Call Web Service Method

In ASP.NET, the client adds a Web Reference/Service Reference, obtains the WSDL, generates a proxy class, and then uses the proxy to call the required Web Service methods.

Example

StudentWS.StudentService svc = new StudentWS.StudentService();
int result = svc.Add(10, 20);

Here, the client is consuming the StudentService Web Service by calling its Add() method.

ADO.NET (ActiveX Data Objects .NET) is a data-access technology in the .NET Framework. It provides classes for connecting to databases, executing commands, and retrieving/manipulating data using both connected and disconnected modes.

Components of ADO.NET

Connected vs Disconnected Data Model

Query String

A Query String is data appended to a URL after the ? (query delimiter). It is used to pass information between pages through the URL. Multiple parameters are separated using &.

https://iqra.ac.in/Profile.aspx?id=5&name=Riya

In ASP.NET, the values can be retrieved using the Request.QueryString collection:

string id = Request.QueryString["id"];
string name = Request.QueryString["name"];

// Passing Query String
Response.Redirect("Profile.aspx?id=" + txtID.Text + "&name=" + txtName.Text);

URL Encoding

Used to encode special characters in data so they can be safely transmitted through a URL. ASP.NET provides Server.UrlEncode().

Response.Redirect("Profile.aspx?id=" + txtID.Text + 
                  "&name=" + Server.UrlEncode(txtName.Text));

If txtName = Riya Sharma, the URL becomes ...name=Riya%20Sharma.

Advantages & Limitations

Session State is a server-side state management technique used to store user-specific data on the server and maintain it between different pages during a user's visit. Since HTTP is stateless, Session helps ASP.NET remember information between requests.

Each user gets a unique Session ID, and the default Session timeout is 20 minutes of inactivity.

Example

// Storing a value
Session["UserName"] = txtName.Text;

// Retrieving
if (Session["UserName"] != null) {
    lblUser.Text = Session["UserName"].ToString();
}

// Removing
Session.Remove("UserName");   // Remove one value
Session.Clear();              // Clear all values
Session.Abandon();            // End the session

Session Modes

Difference between Session, Application and Cookies

State Management is the technique of maintaining data between different requests and pages in an ASP.NET application. This is necessary because HTTP is stateless.

1. Client-Side State Management

Data is maintained on the client/browser.

2. Server-Side State Management

Data is maintained on the web server.

Comparison

A Web Service is a software component accessible over a network that allows different applications to communicate and exchange information using standard protocols. In classic ASP.NET, they use the .asmx extension and expose methods via the [WebMethod] attribute.

Features and Advantages

• 01Platform Independent: Applications on different platforms can communicate.
• 02Language Independent: Client and Service can be in different languages.
• 03Interoperability: Uses standard technologies like HTTP, XML, SOAP.
• 04Reusable: Single service used by multiple applications.
• 05Loosely Coupled: Client only needs to know the service operation/parameters, not internal implementations.

SOAP and WSDL

An ASMX Web Service is a classic ASP.NET Web Service that uses the .asmx extension.

A. Steps to Create an ASMX Web Service

[WebMethod]
public int Add(int a, int b)
{
    return a + b;
}

B. Steps to Consume the ASMX Web Service

Consuming means using the Web Service from a client application.

StudentWS.StudentService svc = new StudentWS.StudentService();
int result = svc.Add(10, 20);
lblResult.Text = result.ToString();

C. Overall Communication Flow

Create ASMX Service
        ↓
Write [WebMethod]
        ↓
Run & Test Service
        ↓
Get WSDL
        ↓
Add Web Reference
        ↓
Proxy Class Generated
        ↓
Client Calls Method
        ↓
SOAP Request
        ↓
Web Service Executes
        ↓
SOAP Response
        ↓
Client Receives Result