SQL Injection (SQLI) is a common attack vector that uses malicious SQL code for backend database manipulation to access information that was not intended to be displayed. It usually occurs when a user provides an SQL statement as input i...

Short Notes (Any Two)

a. Lambda Expression

Definition

A lambda expression is an anonymous function that can be used to create delegates or expression tree types. Lambda expressions are a concise way to write inline functions and are heavily used in LINQ (Language Integrated Query) in C#.

Syntax

(parameters) => expression

or for a block body:

(parameters) => { statements; }

Key Characteristics

• The => operator is called the lambda operator and is read as "goes to".
• Lambda expressions can have zero, one, or multiple parameters.
• They can be used wherever a delegate type is expected.
• They are a core part of LINQ support in C#, alongside query expressions, object initializers, and collections.

Example

// Simple lambda expression
Func<int, int> square = x => x * x;
Console.WriteLine(square(5)); // Output: 25

// Lambda with LINQ
int[] scores = new int[] { 97, 92, 83, 60 };
var highScores = scores.Where(score => score > 80);
foreach (int s in highScores)
    Console.WriteLine(s);
// Output: 97 92 83

Why Use Lambda Expressions?

• Makes code shorter and more readable.
• Eliminates the need to define a separate named method for simple operations.
• Integrates seamlessly with LINQ to query collections, databases, XML, and more.
• Supports functional programming style in C#.

b. Cross Site Request Forgery (CSRF)

Definition

Cross-Site Request Forgery (CSRF) is a web security attack where an attacker tricks an authenticated user into unknowingly submitting a malicious request to a web application on which the user is currently authenticated.

How CSRF Works

1. The user logs into a trusted website (e.g., a banking site) and a session cookie is stored in the browser.
2. Without logging out, the user visits a malicious website.
3. The malicious site contains a hidden request (e.g., a form or image tag) that sends a request to the trusted website.
4. Since the browser automatically includes the session cookie, the trusted website processes the request as if it came from the legitimate user.

Example Attack Scenario

<!-- Malicious page sends a hidden request to the bank -->
<img src="http://bank.com/transfer?amount=10000&to=attacker" />

The browser automatically sends the authenticated cookie along with this request.

Difference from XSS

Prevention Techniques

• Anti-CSRF Tokens: Include a unique, secret token in every form that the server validates.
• SameSite Cookie Attribute: Restricts cookies from being sent with cross-site requests.
• Re-authentication: Require password confirmation for sensitive actions.
• Checking Referer/Origin headers: Validate that requests originate from the expected domain.

c. Single Page Application (SPA)

Definition

A Single Page Application (SPA) is a web application that loads a single HTML page and dynamically updates the content as the user interacts with the app, without requiring a full page reload from the server.

How SPA Works

• On the first request, the server sends a single HTML page along with all necessary JavaScript and CSS.
• Subsequent interactions (navigation, data loading) are handled via AJAX calls to the server, which returns only data (typically JSON), not full HTML pages.
• The browser's JavaScript framework (e.g., Angular, React, Vue.js) updates the DOM dynamically.

Architecture Diagram

User Action --> JavaScript (Client Side) --> AJAX Request --> Server API
                        |                                         |
                   DOM Updated <-------------- JSON Response -----+

Key Characteristics

• Only one full page load occurs (at the start).
• Uses client-side routing to simulate navigation between pages.
• Heavy use of JavaScript frameworks like Angular, React, or Vue.js.
• Communicates with the backend via REST APIs or GraphQL.

Advantages

Disadvantages

• SEO challenges: Search engines may struggle to index dynamically loaded content.
• Initial load time can be slow as all JavaScript is loaded upfront.
• Browser history management requires extra handling.
• Security: Requires careful handling of authentication tokens (e.g., JWT).

Example Technologies

• Frameworks: Angular, React, Vue.js
• Communication: AJAX, Fetch API, Axios
• Routing: React Router, Angular Router

Deploying a .NET Core Application

Introduction

.NET Core is a cross-platform framework, and its Command-Line Interface (CLI) provides tools to build, run, test, and publish .NET Core applications. The .NET Core CLI is installed with the .NET Core SDK and does not need to be installed separately.

Step-by-Step Deployment Procedure

Step 1: Verify .NET Core CLI Installation

Before deploying, confirm that the CLI is properly installed by opening the command prompt and typing:

dotnet

If it displays usage information, the CLI is installed correctly.

Step 2: Create the Application

Create a new project directory and initialize the application using CLI commands:

mkdir myapp
cd myapp
dotnet new console

This creates the necessary project files:

• Program.cs (main source file)
• myapp.csproj (project configuration file)

Step 3: Restore Packages

Restore all required NuGet packages and dependencies:

dotnet restore

This ensures all dependencies defined in the .csproj file are downloaded and available.

Step 4: Build the Application

Compile the application to check for errors and generate the build output:

dotnet build

Note: When using .NET Core SDK, the application is built automatically when needed, so there is no need to worry about executing outdated code.

Step 5: Run the Application (Testing)

Test the application locally before deployment:

dotnet run

This compiles (if needed) and executes the application directly.

Step 6: Publish the Application

Publish the application to prepare it for deployment on a target server:

dotnet publish -c Release -o ./publish

• -c Release specifies the Release configuration (optimized build)
• -o ./publish specifies the output directory where published files are placed

This generates all necessary files (DLLs, configuration files, runtime files) in the output folder.

Step 7: Deploy to the Server

Copy the published output to the target server. For a web application, the deployment typically involves:

• Placing the published files on the server
• Configuring a reverse proxy (such as IIS, Nginx, or Apache)
• The reverse proxy receives requests from the browser and passes them to the ASP.NET Core application, which runs a self-hosted web server (Kestrel)

Browser --> Reverse Proxy (IIS/Nginx) --> ASP.NET Core App (Kestrel)

Summary Table

Conclusion

The .NET Core CLI provides a simple and consistent cross-platform procedure for deploying applications. Higher-level IDEs like Visual Studio internally use the same CLI commands to restore, build, and publish .NET Core applications.

Entity Framework vs ADO.NET and ADO.NET Database Operations

Part 1: Advantages of Entity Framework over ADO.NET

Entity Framework (EF) is an Object/Relational Mapping (O/RM) framework that is an enhancement to ADO.NET giving developers an automated mechanism for accessing and storing data in the database.

Part 2: ADO.NET - Insert Records and Retrieve Fee for CSIT

Database Setup Assumption

• Database Name: IOST
• Table: FACULTY(Course_Name, CourseID, No_of_Semester, fee)

Step 1: Create the Table in SQL Server (for reference)

CREATE DATABASE IOST;

USE IOST;

CREATE TABLE FACULTY (
    Course_Name    VARCHAR(100),
    CourseID       INT PRIMARY KEY,
    No_of_Semester INT,
    fee            DECIMAL(10, 2)
);

Step 2: Full ADO.NET C# Code - Insert Records and Retrieve Fee for CSIT

using System;
using System.Data;
using System.Data.SqlClient;

namespace IOSTFacultyApp
{
    class Program
    {
        // Connection string pointing to IOST database
        static string connectionString = 
            "Data Source=.;Initial Catalog=IOST;Integrated Security=True";

        static void Main(string[] args)
        {
            // Step 1: Insert records into FACULTY table
            InsertFaculty("CSIT",   1, 8, 75000.00m);
            InsertFaculty("BCA",    2, 6, 55000.00m);
            InsertFaculty("CSIT",   3, 8, 80000.00m);
            InsertFaculty("BIT",    4, 8, 60000.00m);

            Console.WriteLine("Records inserted successfully.\n");

            // Step 2: Retrieve fee of records where Course_Name = 'CSIT'
            RetrieveCSITFee();

            Console.ReadLine();
        }

        // -------------------------------------------------------
        // Method to INSERT a record into FACULTY table
        // -------------------------------------------------------
        static void InsertFaculty(string courseName, int courseID, 
                                   int noOfSemester, decimal fee)
        {
            // SQL INSERT query using parameterized query to prevent SQL injection
            string insertQuery = @"INSERT INTO FACULTY 
                                   (Course_Name, CourseID, No_of_Semester, fee) 
                                   VALUES 
                                   (@CourseName, @CourseID, @NoOfSemester, @Fee)";

            // Using block ensures connection is closed automatically
            using (SqlConnection con = new SqlConnection(connectionString))
            {
                using (SqlCommand cmd = new SqlCommand(insertQuery, con))
                {
                    // Add parameters to avoid SQL injection
                    cmd.Parameters.AddWithValue("@CourseName",    courseName);
                    cmd.Parameters.AddWithValue("@CourseID",      courseID);
                    cmd.Parameters.AddWithValue("@NoOfSemester",  noOfSemester);
                    cmd.Parameters.AddWithValue("@Fee",           fee);

                    // Open connection
                    con.Open();

                    // Execute the INSERT command
                    int rowsAffected = cmd.ExecuteNonQuery();

                    Console.WriteLine($"Inserted: {courseName} | Rows Affected: {rowsAffected}");
                }
                // Connection is closed automatically at end of using block
            }
        }

        // -------------------------------------------------------
        // Method to RETRIEVE fee of FACULTY records where 
        // Course_Name = 'CSIT'
        // -------------------------------------------------------
        static void RetrieveCSITFee()
        {
            // SQL SELECT query with WHERE clause to filter CSIT records
            string selectQuery = @"SELECT Course_Name, CourseID, 
                                          No_of_Semester, fee 
                                   FROM FACULTY 
                                   WHERE Course_Name = @CourseName";

            using (SqlConnection con = new SqlConnection(connectionString))
            {
                using (SqlCommand cmd = new SqlCommand(selectQuery, con))
                {
                    // Parameterized filter for Course_Name
                    cmd.Parameters.AddWithValue("@CourseName, "CSIT");

                    con.Open();

                    // Execute the query and read results row by row
                    SqlDataReader reader = cmd.ExecuteReader();

                    Console.WriteLine("Fee details for CSIT:");
                    Console.WriteLine("Course_Name | CourseID | No_of_Semester | Fee");

                    while (reader.Read())
                    {
                        Console.WriteLine(
                            $"{reader["Course_Name"]} | {reader["CourseID"]} | " +
                            $"{reader["No_of_Semester"]} | {reader["fee"]}"
                        );
                    }

                    reader.Close();
                }
                // Connection is closed automatically at end of using block
            }
        }
    }
}

The InsertFaculty method uses a parameterized INSERT with AddWithValue for every field, guarding against SQL injection while adding the four faculty records (two of which are CSIT). The RetrieveCSITFee method then runs a parameterized SELECT ... WHERE Course_Name = @CourseName filtered to "CSIT", opens a SqlDataReader, and loops over reader.Read() to print each matching row's course name, course ID, number of semesters, and fee, giving exactly the fee details for the CSIT records that were inserted.

Session State is an ASP.NET Core mechanism to store user data while the user browses the application. It uses a store maintained by the application to carry on data across requests from a client. ASP.NET Core maintains the session state ...

SQL Injection (SQLI) is a common attack vector that uses malicious SQL code for backend database manipulation to access information that was not intended to be displayed. It usually occurs when a user provides an SQL statement as input i...

Deploying a .NET Core Application

Introduction

.NET Core is a cross-platform framework, and its Command-Line Interface (CLI) provides tools to build, run, test, and publish .NET Core applications. The .NET Core CLI is installed with the .NET Core SDK and does not need to be installed separately.

Step-by-Step Deployment Procedure

Step 1: Verify .NET Core CLI Installation

Before deploying, confirm that the CLI is properly installed by opening the command prompt and typing:

dotnet

If it displays usage information, the CLI is installed correctly.

Step 2: Create the Application

Create a new project directory and initialize the application using CLI commands:

mkdir myapp
cd myapp
dotnet new console

This creates the necessary project files:

• Program.cs (main source file)
• myapp.csproj (project configuration file)

Step 3: Restore Packages

Restore all required NuGet packages and dependencies:

dotnet restore

This ensures all dependencies defined in the .csproj file are downloaded and available.

Step 4: Build the Application

Compile the application to check for errors and generate the build output:

dotnet build

Note: When using .NET Core SDK, the application is built automatically when needed, so there is no need to worry about executing outdated code.

Step 5: Run the Application (Testing)

Test the application locally before deployment:

dotnet run

This compiles (if needed) and executes the application directly.

Step 6: Publish the Application

Publish the application to prepare it for deployment on a target server:

dotnet publish -c Release -o ./publish

• -c Release specifies the Release configuration (optimized build)
• -o ./publish specifies the output directory where published files are placed

This generates all necessary files (DLLs, configuration files, runtime files) in the output folder.

Step 7: Deploy to the Server

Copy the published output to the target server. For a web application, the deployment typically involves:

• Placing the published files on the server
• Configuring a reverse proxy (such as IIS, Nginx, or Apache)
• The reverse proxy receives requests from the browser and passes them to the ASP.NET Core application, which runs a self-hosted web server (Kestrel)

Browser --> Reverse Proxy (IIS/Nginx) --> ASP.NET Core App (Kestrel)

Summary Table

Conclusion

The .NET Core CLI provides a simple and consistent cross-platform procedure for deploying applications. Higher-level IDEs like Visual Studio internally use the same CLI commands to restore, build, and publish .NET Core applications.

Entity Framework vs ADO.NET and ADO.NET Database Operations

Part 1: Advantages of Entity Framework over ADO.NET

Entity Framework (EF) is an Object/Relational Mapping (O/RM) framework that is an enhancement to ADO.NET giving developers an automated mechanism for accessing and storing data in the database.

Part 2: ADO.NET - Insert Records and Retrieve Fee for CSIT

Database Setup Assumption

• Database Name: IOST
• Table: FACULTY(Course_Name, CourseID, No_of_Semester, fee)

Step 1: Create the Table in SQL Server (for reference)

CREATE DATABASE IOST;

USE IOST;

CREATE TABLE FACULTY (
    Course_Name    VARCHAR(100),
    CourseID       INT PRIMARY KEY,
    No_of_Semester INT,
    fee            DECIMAL(10, 2)
);

Step 2: Full ADO.NET C# Code - Insert Records and Retrieve Fee for CSIT

using System;
using System.Data;
using System.Data.SqlClient;

namespace IOSTFacultyApp
{
    class Program
    {
        // Connection string pointing to IOST database
        static string connectionString = 
            "Data Source=.;Initial Catalog=IOST;Integrated Security=True";

        static void Main(string[] args)
        {
            // Step 1: Insert records into FACULTY table
            InsertFaculty("CSIT",   1, 8, 75000.00m);
            InsertFaculty("BCA",    2, 6, 55000.00m);
            InsertFaculty("CSIT",   3, 8, 80000.00m);
            InsertFaculty("BIT",    4, 8, 60000.00m);

            Console.WriteLine("Records inserted successfully.\n");

            // Step 2: Retrieve fee of records where Course_Name = 'CSIT'
            RetrieveCSITFee();

            Console.ReadLine();
        }

        // -------------------------------------------------------
        // Method to INSERT a record into FACULTY table
        // -------------------------------------------------------
        static void InsertFaculty(string courseName, int courseID, 
                                   int noOfSemester, decimal fee)
        {
            // SQL INSERT query using parameterized query to prevent SQL injection
            string insertQuery = @"INSERT INTO FACULTY 
                                   (Course_Name, CourseID, No_of_Semester, fee) 
                                   VALUES 
                                   (@CourseName, @CourseID, @NoOfSemester, @Fee)";

            // Using block ensures connection is closed automatically
            using (SqlConnection con = new SqlConnection(connectionString))
            {
                using (SqlCommand cmd = new SqlCommand(insertQuery, con))
                {
                    // Add parameters to avoid SQL injection
                    cmd.Parameters.AddWithValue("@CourseName",    courseName);
                    cmd.Parameters.AddWithValue("@CourseID",      courseID);
                    cmd.Parameters.AddWithValue("@NoOfSemester",  noOfSemester);
                    cmd.Parameters.AddWithValue("@Fee",           fee);

                    // Open connection
                    con.Open();

                    // Execute the INSERT command
                    int rowsAffected = cmd.ExecuteNonQuery();

                    Console.WriteLine($"Inserted: {courseName} | Rows Affected: {rowsAffected}");
                }
                // Connection is closed automatically at end of using block
            }
        }

        // -------------------------------------------------------
        // Method to RETRIEVE fee of FACULTY records where 
        // Course_Name = 'CSIT'
        // -------------------------------------------------------
        static void RetrieveCSITFee()
        {
            // SQL SELECT query with WHERE clause to filter CSIT records
            string selectQuery = @"SELECT Course_Name, CourseID, 
                                          No_of_Semester, fee 
                                   FROM FACULTY 
                                   WHERE Course_Name = @CourseName";

            using (SqlConnection con = new SqlConnection(connectionString))
            {
                using (SqlCommand cmd = new SqlCommand(selectQuery, con))
                {
                    // Parameterized filter for Course_Name
                    cmd.Parameters.AddWithValue("@CourseName, "CSIT");

                    con.Open();

                    // Execute the query and read results row by row
                    SqlDataReader reader = cmd.ExecuteReader();

                    Console.WriteLine("Fee details for CSIT:");
                    Console.WriteLine("Course_Name | CourseID | No_of_Semester | Fee");

                    while (reader.Read())
                    {
                        Console.WriteLine(
                            $"{reader["Course_Name"]} | {reader["CourseID"]} | " +
                            $"{reader["No_of_Semester"]} | {reader["fee"]}"
                        );
                    }

                    reader.Close();
                }
                // Connection is closed automatically at end of using block
            }
        }
    }
}

The InsertFaculty method uses a parameterized INSERT with AddWithValue for every field, guarding against SQL injection while adding the four faculty records (two of which are CSIT). The RetrieveCSITFee method then runs a parameterized SELECT ... WHERE Course_Name = @CourseName filtered to "CSIT", opens a SqlDataReader, and loops over reader.Read() to print each matching row's course name, course ID, number of semesters, and fee, giving exactly the fee details for the CSIT records that were inserted.

Short Notes (Any Two)

a. Lambda Expression

Definition

A lambda expression is an anonymous function that can be used to create delegates or expression tree types. Lambda expressions are a concise way to write inline functions and are heavily used in LINQ (Language Integrated Query) in C#.

Syntax

(parameters) => expression

or for a block body:

(parameters) => { statements; }

Key Characteristics

• The => operator is called the lambda operator and is read as "goes to".
• Lambda expressions can have zero, one, or multiple parameters.
• They can be used wherever a delegate type is expected.
• They are a core part of LINQ support in C#, alongside query expressions, object initializers, and collections.

Example

// Simple lambda expression
Func<int, int> square = x => x * x;
Console.WriteLine(square(5)); // Output: 25

// Lambda with LINQ
int[] scores = new int[] { 97, 92, 83, 60 };
var highScores = scores.Where(score => score > 80);
foreach (int s in highScores)
    Console.WriteLine(s);
// Output: 97 92 83

Why Use Lambda Expressions?

• Makes code shorter and more readable.
• Eliminates the need to define a separate named method for simple operations.
• Integrates seamlessly with LINQ to query collections, databases, XML, and more.
• Supports functional programming style in C#.

b. Cross Site Request Forgery (CSRF)

Definition

Cross-Site Request Forgery (CSRF) is a web security attack where an attacker tricks an authenticated user into unknowingly submitting a malicious request to a web application on which the user is currently authenticated.

How CSRF Works

1. The user logs into a trusted website (e.g., a banking site) and a session cookie is stored in the browser.
2. Without logging out, the user visits a malicious website.
3. The malicious site contains a hidden request (e.g., a form or image tag) that sends a request to the trusted website.
4. Since the browser automatically includes the session cookie, the trusted website processes the request as if it came from the legitimate user.

Example Attack Scenario

<!-- Malicious page sends a hidden request to the bank -->
<img src="http://bank.com/transfer?amount=10000&to=attacker" />

The browser automatically sends the authenticated cookie along with this request.

Difference from XSS

Prevention Techniques

• Anti-CSRF Tokens: Include a unique, secret token in every form that the server validates.
• SameSite Cookie Attribute: Restricts cookies from being sent with cross-site requests.
• Re-authentication: Require password confirmation for sensitive actions.
• Checking Referer/Origin headers: Validate that requests originate from the expected domain.

c. Single Page Application (SPA)

Definition

A Single Page Application (SPA) is a web application that loads a single HTML page and dynamically updates the content as the user interacts with the app, without requiring a full page reload from the server.

How SPA Works

• On the first request, the server sends a single HTML page along with all necessary JavaScript and CSS.
• Subsequent interactions (navigation, data loading) are handled via AJAX calls to the server, which returns only data (typically JSON), not full HTML pages.
• The browser's JavaScript framework (e.g., Angular, React, Vue.js) updates the DOM dynamically.

Architecture Diagram

User Action --> JavaScript (Client Side) --> AJAX Request --> Server API
                        |                                         |
                   DOM Updated <-------------- JSON Response -----+

Key Characteristics

• Only one full page load occurs (at the start).
• Uses client-side routing to simulate navigation between pages.
• Heavy use of JavaScript frameworks like Angular, React, or Vue.js.
• Communicates with the backend via REST APIs or GraphQL.

Advantages

Disadvantages

• SEO challenges: Search engines may struggle to index dynamically loaded content.
• Initial load time can be slow as all JavaScript is loaded upfront.
• Browser history management requires extra handling.
• Security: Requires careful handling of authentication tokens (e.g., JWT).

Example Technologies

• Frameworks: Angular, React, Vue.js
• Communication: AJAX, Fetch API, Axios
• Routing: React Router, Angular Router

Session State is an ASP.NET Core mechanism to store user data while the user browses the application. It uses a store maintained by the application to carry on data across requests from a client. ASP.NET Core maintains the session state ...

Roles vs Policies and Kestrel Web Server in ASP.NET Core

Part 1: Distinguish Between Roles and Policies

Part 2: Kestrel Web Server in ASP.NET Core

Definition

Kestrel is a cross-platform, lightweight web server for ASP.NET Core. It is the web server that is included by default in ASP.NET Core project templates and is built into the ASP.NET Core framework.

Key Features of Kestrel

• Cross-platform: Kestrel runs on Windows, Linux, and macOS, making ASP.NET Core applications truly cross-platform.
• Default web server: It is automatically included when an ASP.NET Core project is created using the default templates.
• High performance: Kestrel is designed to be fast and efficient for handling HTTP requests.
• Self-hosted: It can run independently without requiring an external web server.

Hosting Models Using Kestrel

There are two ways Kestrel is used in the Out-of-Process Hosting Model:

1. Using Kestrel Directly (Edge Server)

• Kestrel itself acts as an edge server, which directly serves user requests from the internet.
• No additional web server (like IIS or NGINX) is needed.
• Suitable for simpler applications or internal services.

Browser Request --> Kestrel Server --> ASP.NET Core Application

2. Using Kestrel with a Reverse Proxy Server

• Due to limitations of Kestrel, it cannot be used in all scenarios (e.g., sharing a port, advanced security features).
• In such cases, powerful servers like IIS, NGINX, or Apache act as a reverse proxy server.
• The reverse proxy receives the request from the browser and redirects/forwards it to the internal Kestrel server.
• Kestrel then processes the request and returns the response.

Browser Request --> Reverse Proxy (IIS/NGINX/Apache) --> Kestrel Server --> ASP.NET Core App

In-Process Hosting (IIS)

• In this model, the ASP.NET Core app is hosted inside the IIS worker process (w3wp.exe).
• IIS forwards web requests to the backend ASP.NET Core app running the Kestrel server (out-of-process hosting model).

Summary

Kestrel is the heart of ASP.NET Core's web serving capability. It provides a fast, cross-platform, and lightweight server that can either work standalone as an edge server or work behind a powerful reverse proxy like IIS or NGINX for production-grade deployments.

Life Cycle of Dependency Injection (DI) Container

In ASP.NET Core, the built-in IoC (Inversion of Control) container manages the creation and lifetime of service instances. The lifetime of a service defines how long an instance lives and when a new instance is created. There are three main service lifetimes:

1. Transient

• The IoC container creates a new instance every time the service is requested.
• Each call to resolve the service produces a fresh object.
• Best suited for lightweight, stateless services.

Registration Example:

services.Add(new ServiceDescriptor(
    typeof(ILog),
    typeof(MyConsoleLogger),
    ServiceLifetime.Transient));

Use case: A simple utility/helper service that holds no shared state.

2. Scoped

• The IoC container creates one instance per HTTP request and shares that same instance throughout the entire request.
• Different requests get different instances.
• Best suited for services that need to maintain state within a single request (e.g., database context).

Registration Example:

services.Add(new ServiceDescriptor(
    typeof(ILog),
    typeof(MyConsoleLogger),
    ServiceLifetime.Scoped));

Use case: A database context or unit-of-work that should be consistent within one request.

3. Singleton

• The IoC container creates only one instance for the entire application lifetime.
• The same instance is reused for every request and every user.
• Best suited for services that are stateless and expensive to create, or that hold shared application-wide state.

Registration Example:

services.Add(new ServiceDescriptor(
    typeof(ILog),
    new MyConsoleLogger())); // single instance passed directly

Use case: A logging service or configuration service shared across the whole application.

Summary Table

How Registration Works

Services are registered inside the ConfigureServices() method in Startup.cs:

public void ConfigureServices(IServiceCollection services)
{
    // Singleton
    services.Add(new ServiceDescriptor(typeof(ILog), new MyConsoleLogger()));

    // Transient
    services.Add(new ServiceDescriptor(typeof(ILog),
        typeof(MyConsoleLogger), ServiceLifetime.Transient));

    // Scoped
    services.Add(new ServiceDescriptor(typeof(ILog),
        typeof(MyConsoleLogger), ServiceLifetime.Scoped));
}

Once registered, the IoC container automatically injects the service via constructor injection wherever the service type is used as a constructor parameter, without the developer needing to manually instantiate it.

Managing State on Stateless HTTP and Form Validation Using jQuery

Part 1: Managing State on Stateless HTTP (5 marks)

What is the Problem?

HTTP is a stateless protocol, meaning each request from a client to the server is independent. The server does not remember any previous request. However, real-world web applications (like shopping carts, login sessions, etc.) need to remember user data across multiple requests. This is called state management.

State Management Approaches in ASP.NET

The following storage approaches are used to manage state on stateless HTTP:

Detailed Explanation of Each Approach

1. Cookies

• Small pieces of data stored on the client's browser.
• Sent automatically with every HTTP request to the server.
• Used to remember user preferences, login tokens, etc.

// Setting a cookie in ASP.NET MVC
Response.Cookies.Append("Username", "JohnDoe");

// Reading a cookie
string username = Request.Cookies["Username"];

Limitation: Cookies can be tampered with by the client, so sensitive data should not be stored directly.

2. Session State

• Data is stored on the server side.
• A unique session ID is stored in a cookie on the client side.
• The server uses this ID to retrieve the corresponding session data.

// Storing data in session
HttpContext.Session.SetString("UserName", "JohnDoe");

// Retrieving data from session
string name = HttpContext.Session.GetString("UserName");

Advantage: More secure than cookies since actual data stays on the server.

3. TempData

• Used to pass data between two consecutive requests (e.g., from one action to another after a redirect).
• Internally uses cookies or session state.

// Storing in TempData
TempData["Message"] = "Record saved successfully!";

// Reading in the next request
string msg = TempData["Message"].ToString();

4. Query Strings

• Data is passed as part of the URL.

https://example.com/products?category=electronics&page=2

string category = Request.Query["category"];

Limitation: Visible in the URL, not suitable for sensitive data.

5. Hidden Fields

• Data is stored in HTML form fields that are not visible to the user but are submitted with the form.

<input type="hidden" name="UserId" value="101" />

Limitation: Can be viewed and modified by inspecting the page source.

6. Cache

• Data is stored server-side in memory for fast access.
• Suitable for data that is expensive to compute and shared across users.

// Using IMemoryCache
_cache.Set("ProductList", products, TimeSpan.FromMinutes(10));

Summary Diagram

Client (Browser)                    Server
     |                                 |
     |--- HTTP Request (stateless) --->|
     |                                 |
     |  State managed via:             |
     |  - Cookies (client-side)        |
     |  - Session (server-side)        |
     |  - TempData (redirect)          |
     |  - Query Strings (URL)          |
     |  - Hidden Fields (form)         |
     |  - Cache (server memory)        |
     |<-- HTTP Response ---------------|

Part 2: Form Validation Using jQuery (5 marks)

What is jQuery Form Validation?

jQuery provides a simple and powerful way to validate HTML forms on the client side before the data is submitted to the server. This improves user experience by giving instant feedback without a page reload.

The most commonly used plugin is the jQuery Validation Plugin.

Assumptions

• We have a Student Registration Form with fields: Name, Email, Age, and Password.
• jQuery and jQuery Validation plugin are included via CDN.
• Validation is done client-side before form submission.

Step 1: HTML Form Structure

<!DOCTYPE html>
<html>
<head>
    <title>Student Registration</title>
    <!-- Include jQuery -->
    <script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
    <!-- Include jQuery Validation Plugin -->
    <script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/jquery.validate.min.js"></script>
    <style>
        .error { color: red; font-size: 12px; }
        input { display: block; margin: 8px 0; padding: 5px; }
    </style>
</head>
<body>

<h2>Student Registration Form</h2>

<form id="registrationForm">
    <label>Full Name:</label>
    <input type="text" id="name" name="name" placeholder="Enter your name" />

    <label>Email:</label>
    <input type="email" id="email" name="email" placeholder="Enter your email" />

    <label>Age:</label>
    <input type="number" id="age" name="age" placeholder="Enter your age" />

    <label>Password:</label>
    <input type="password" id="password" name="password" placeholder="Enter password" />

    <label>Confirm Password:</label>
    <input type="password" id="confirmPassword" name="confirmPassword"
           placeholder="Confirm password" />

    <button type="submit">Register</button>
</form>

</body>
</html>

Step 2: jQuery Validation Script

<script>
$(document).ready(function () {
    $("#registrationForm").validate({
        rules: {
            name: {
                required: true,
                minlength: 3
            },
            email: {
                required: true,
                email: true
            },
            age: {
                required: true,
                number: true,
                min: 16,
                max: 100
            },
            password: {
                required: true,
                minlength: 6
            },
            confirmPassword: {
                required: true,
                equalTo: "#password"
            }
        },
        messages: {
            name: "Please enter your full name (at least 3 characters).",
            email: "Please enter a valid email address.",
            age: "Age must be between 16 and 100.",
            password: "Password must be at least 6 characters long.",
            confirmPassword: "Passwords do not match."
        },
        submitHandler: function (form) {
            alert("Registration form is valid! Submitting...");
            form.submit();
        }
    });
});
</script>

The jQuery Validation Plugin's .validate() call attaches a rules object (what each field must satisfy) and a matching messages object (what to show when a rule fails) directly to the form, and it re-checks every field automatically on blur and on keyup, so the student sees an inline error the moment a field becomes invalid, without any page reload. The submitHandler only fires once every rule passes, at which point the form is genuinely submitted to the server, giving the registration page instant client-side feedback backed by the plugin's built-in required, email, number, minlength, and equalTo validators.

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jQuery Form Validation - Username, Password, and Phone Number

Complete Solution

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Form Validation using jQuery</title>

    <!-- jQuery CDN -->
    <script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>

    <style>
        body {
            font-family: Arial, sans-serif;
            margin: 50px;
        }
        .error {
            color: red;
            font-size: 13px;
        }
        .success {
            color: green;
            font-size: 14px;
        }
        input {
            display: block;
            margin: 5px 0 2px 0;
            padding: 6px;
            width: 250px;
        }
        label {
            font-weight: bold;
            margin-top: 10px;
            display: block;
        }
        button {
            margin-top: 15px;
            padding: 8px 20px;
        }
    </style>
</head>
<body>

<h2>User Registration Form</h2>

<form id="registrationForm">

    <label for="username">Username:</label>
    <input type="text" id="username" placeholder="Enter username" />
    <span class="error" id="usernameError"></span>

    <label for="password">Password:</label>
    <input type="password" id="password" placeholder="Enter password" />
    <span class="error" id="passwordError"></span>

    <label for="phone">Phone Number:</label>
    <input type="text" id="phone" placeholder="Enter 10-digit phone number" />
    <span class="error" id="phoneError"></span>

    <button type="submit">Submit</button>

    <p id="successMsg" class="success"></p>

</form>

<script>
    $(document).ready(function () {

        // Handle form submission
        $("#registrationForm").submit(function (event) {

            // Prevent default form submission
            event.preventDefault();

            // Clear previous error messages
            $(".error").text("");
            $("#successMsg").text("");

            // Get field values and trim whitespace
            var username = $("#username").val().trim();
            var password = $("#password").val().trim();
            var phone    = $("#phone").val().trim();

            var isValid = true;

            // Validate Username - must be non-empty
            if (username === "") {
                $("#usernameError").text("Username is required.");
                isValid = false;
            }

            // Validate Password - must be non-empty
            if (password === "") {
                $("#passwordError").text("Password is required.");
                isValid = false;
            }

            // Validate Phone - must be non-empty AND exactly 10 digits
            if (phone === "") {
                $("#phoneError").text("Phone number is required.");
                isValid = false;
            } else if (!/^\d{10}$/.test(phone)) {
                $("#phoneError").text("Phone number must contain exactly 10 digits.");
                isValid = false;
            }

            // If all validations pass
            if (isValid) {
                $("#successMsg").text("Form submitted successfully!");
            }
        });
    });
</script>

</body>
</html>

Explanation of Key Parts

Validation Rules Applied

1. Username - must not be empty
2. Password - must not be empty
3. Phone Number - must not be empty AND must contain exactly 10 digits (no letters or special characters allowed)