Maintaining consistency across numerous processes can be difficult in the world of distributed systems and microservices architecture. The Saga pattern saves the day by managing a series of distributed transactions to ensure data consistency without relying on a two-phase commit process. In this post, we'll look at how to implement the Saga pattern with Rebus, a versatile.NET messaging package, and RabbitMQ, a sophisticated message broker.

What exactly is the Saga Pattern?
The Saga pattern, at its core, maintains a chain of local transactions, with each step representing a transaction involving distinct services or components. If any step fails, compensating actions are taken to ensure overall consistency.

Sagas ensure that either all operations within the sequence succeed or, in the case of failure, the system reverts to a consistent state by executing compensating actions.
Using Rebus and RabbitMQ

Setting Up Rebus and RabbitMQ

To begin, install the necessary packages using NuGet.
Install-Package Rebus
Install-Package Rebus.RabbitMQ

Next, configure Rebus and RabbitMQ:
var configurer = Configure.With(...)
    .Transport(t => t.UseRabbitMq("amqp://localhost", "saga-example"))
    .Start();

Implementing a Saga
Let's consider a hypothetical e-commerce scenario where a customer places an order consisting of multiple steps: reserve items, charge payment, and ship items. We'll implement a saga to manage these operations.
public class OrderSagaData
{
    public Guid OrderId { get; set; }
    public bool ItemsReserved { get; set; }
    public bool PaymentCharged { get; set; }
    public bool ItemsShipped { get; set; }
}

public class OrderSaga : Saga<OrderSagaData>,
    IAmInitiatedBy<PlaceOrder>,
    IHandleMessages<ReserveItems>,
    IHandleMessages<ChargePayment>,
    IHandleMessages<ShipItems>
{
    // Saga implementation here
}

Handling Messages in the Saga
Each message represents a step in the saga. For instance, the PlaceOrder message initiates the saga.
public class PlaceOrder
{
    public Guid OrderId { get; set; }
    public List<Item> Items { get; set; }
}

public async Task Handle(PlaceOrder message)
{
    Data.OrderId = message.OrderId;
    // Reserve items logic
    Bus.Send(new ReserveItems { OrderId = message.OrderId, Items = message. Items });
}

Similarly, other messages like ReserveItems, ChargePayment, and ShipItems are handled within the saga, managing the respective operations and updating saga data accordingly.

Compensating Actions
Should any step fail, compensating actions ensure the system maintains consistency. For instance, if charging payment fails, a compensating action might be implemented as follows.
public async Task Handle(ChargePayment message)
{
    // Charge payment logic
    if (paymentFailed)
    {
        // Execute compensating action
        Bus.Send(new CancelOrder { OrderId = Data.OrderId });
    }
}

Implementing the Saga pattern using Rebus and RabbitMQ offers a powerful way to manage distributed transactions and maintain data consistency in a microservices architecture. By orchestrating a sequence of steps and incorporating compensating actions, sagas ensure system integrity despite failures within the distributed environment.

The Visitor Pattern is used in an ASP.NET Core Web API with a 3-tier design for efficient data manipulation in the C# Article model. The model, CSharpArticle, contains critical features. A Data Access Layer with a repository manages database interactions, a Business Layer with the Visitor interface and Article Service, and a Presentation Layer with the API controllers comprise the architecture. In the Business Layer, the Visitor Pattern is used to conduct operations on articles, allowing for clean separation of responsibilities and enabling reusable, structured, and scalable code. This architecture ensures that CRUD activities benefit from the flexibility of the Visitor Pattern while preserving a clear division of responsibilities across the application layers.

Overview of Three-Tier Architecture
The Presentation Layer manages the API controllers and interacts with the client.
The business logic, data validation, and any special business rules are all contained in the business layer.
Data Access Layer: Manages data retrieval and storage, as well as database interaction.

Article Model in C#
Let's start with the Article model.
public class CSharpArticle
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }
}

Data Access Layer
Repository Interface:
public interface IArticleRepository
{
    CSharpArticle GetArticleById(int id);
    void AddArticle(CSharpArticle article);
    void UpdateArticle(CSharpArticle article);
    void DeleteArticle(int id);
}

Repository Implementation:
public class ArticleRepository: IArticleRepository
{
    private readonly CSharpCornerArticleProject _context;

    public ArticleRepository(YourDbContext context)
    {
        _context = context;
    }

    public CSharpArticle GetArticleById(int id)
    {
        return _context.Articles.FirstOrDefault(a => a.Id == id);
    }

    public void AddArticle(CSharpArticle article)
    {
        _context.Articles.Add(article);
        _context.SaveChanges();
    }

    public void UpdateArticle(CSharpArticle article)
    {
        _context.Articles.Update(article);
        _context.SaveChanges();
    }

    public void DeleteArticle(int id)
    {
        var article = _context.Articles.FirstOrDefault(a => a.Id == id);
        if (article != null)
        {
            _context.Articles.Remove(article);
            _context.SaveChanges();
        }
    }

    public void Accept(IArticleVisitor visitor, int articleId)
    {
        var article = GetArticleById(articleId);
        visitor.Visit(article);
        UpdateArticle(article);
    }
}

Business Layer
Visitor Interface
public interface IArticleVisitor
{
    void Visit(CSharpArticle article);
}

public class ContentAnalyzerVisitor: IArticleVisitor
{
    public void Visit(CSharpArticle article)
    {
        if (article != null)
        {
            int wordCount = CountWords(article.Content);
            bool hasKeywords = CheckForKeywords(article.Content);

            article.WordCount = wordCount;
            article.HasKeywords = hasKeywords;
        }
    }

    private int CountWords(string content)
    {
        if (string.IsNullOrWhiteSpace(content))
            return 0;

        string[] words = content.Split(new char[] { ' ', '.', ',', ';', '!', '?' }, StringSplitOptions.RemoveEmptyEntries);
        return words.Length;
    }

    private bool CheckForKeywords(string content)
    {
        string[] keywordsToCheck = { "C#", "ASP.NET", "Entity Framework" }; if needed
        foreach (string keyword in keywordsToCheck)
        {
            if (content.Contains(keyword, StringComparison.OrdinalIgnoreCase))
            {
                return true;
            }
        }
        return false;
    }
}

Article Service:
public class ArticleService
{
    private readonly IArticleRepository _repository;

    public ArticleService(IArticleRepository repository)
    {
        _repository = repository;
    }

    public void Accept(IArticleVisitor visitor, int articleId)
    {
        CSharpArticle article = _repository.GetArticleById(articleId);
        visitor.Visit(article);
        _repository.UpdateArticle(article);
    }

    public void Publish(int articleId)
    {
        CSharpArticle article = _repository.GetArticleById(articleId);
        article.Publish();
        _repository.UpdateArticle(article);
    }

    public void Archive(int articleId)
    {
        CSharpArticle article = _repository.GetArticleById(articleId);
        article.Archive();
        _repository.UpdateArticle(article);
    }
}

Presentation Layer (Controller)
Controller:
[Route("api/articles")]
[ApiController]
public class CSharpArticleController : ControllerBase
{
    private readonly ArticleService _articleService;

    public CSharpArticleController(ArticleService articleService)
    {
        _articleService = articleService;
    }

    [HttpGet("{id}")]
    public IActionResult Get(int id)
    {
        var article = _articleService.GetArticle(id);
        if (article == null)
        {
            return NotFound();
        }
        return Ok(article);
    }

    [HttpPost]
    public IActionResult Post([FromBody] CSharpArticle article)
    {
        if (article == null)
        {
            return BadRequest();
        }
        _articleService.CreateArticle(article);
        return CreatedAtAction("Get", new { id = article.Id }, article);
    }

    [HttpPut("{id}")]
    public IActionResult Put(int id, [FromBody] CSharpArticle article)
    {
        if (id != article.Id)
        {
            return BadRequest();
        }
        _articleService.UpdateArticle(article);
        return NoContent();
    }

    [HttpDelete("{id}")]
    public IActionResult Delete(int id)
    {
        var existingArticle = _articleService.GetArticle(id);
        if (existingArticle == null)
        {
            return NotFound();
        }
        _articleService.DeleteArticle(id);
        return NoContent();
    }
}

Conclusion
This structure separates concerns and enables the Visitor Pattern to conduct actions on the Article model across levels, maintaining logical separation and reusability. The repository, service, and controller implementations may alter depending on the database, ORM, or particular requirements of your application. While the Visitor Pattern can be useful in some situations, it may not be required for every CRUD action. Always evaluate the pattern's true need in the context of your application's complexity and requirements.

The implementation of the Visitor Pattern for C# Article management in an ASP.NET Core Web API following a 3-tier design provides a strong structure for managing CRUD activities. The CSharpArticle model is at the heart of data operations, which are governed by the Data Access Layer via the ArticleRepository. This repository communicates with the database and supports CRUD operations. The Business Layer, represented by the ArticleService, orchestrates operations on articles by utilizing the Visitor Pattern to perform specified tasks via visitors such as content analysis, publishing, archiving, and other appropriate actions.The Presentation Layer's CSharpArticleController serves as the interface for external interactions. It interfaces with the ArticleService to handle HTTP requests, allowing it to get, create, update, and delete articles. Each method correlates to an HTTP verb, allowing for smooth communication with the underlying layers and, ultimately, efficient and controlled article administration.

This hierarchical architecture enables code that is modular, scalable, and maintainable. It allows the program to handle additional features or changes without interfering with core functionality. The application of the Visitor Pattern within the three-tier architecture increases the system's flexibility by fostering a clear separation of responsibilities and improving the API's overall performance and maintainability.

Many applications demand the ability to generate PDF documents programmatically. GrapeCity's GcPdf is a comprehensive library in the.NET ecosystem that allows developers to easily generate, change, and manipulate PDF documents. This blog post will show you how to utilize GcPdf to generate PDF documents programmatically in.NET C#, with actual examples to back it up.

What exactly is GcPdf?
GcPdf is a.NET package that offers extensive PDF document production and manipulation features. It has a variety of features, including:

• Creating PDF documents from the ground up.
• Text, photos, and shapes can be added to PDF pages.
• Changing fonts and styles.
• Making tables and graphs.
• Inserting links and bookmarks.
• Exporting PDFs to various formats.
• Password protection and encryption are being added as security measures.

Let's get started with GcPdf by creating a simple PDF document.

How to Begin with GcPdf?
Make sure you have Visual Studio or your favourite C# development environment installed before we begin. In addition, you must include the GrapeCity Documents for PDF NuGet package (GcPdf) in your project.

Making a Basic PDF Document
In this example, we'll make a simple PDF file with text and a rectangle shape.

using System;
using GrapeCity.Documents.Pdf;
using GrapeCity.Documents.Text;

class Program
{
    static void Main(string[] args)
    {
        // Create a new PDF document
        var doc = new GcPdfDocument();

        // Add a page to the document
        var page = doc.NewPage();

        // Create a graphics object for drawing on the page
        var g = page.Graphics;

        // Add content to the page
        var text = "Hello, World!";
        var font = StandardFonts.Helvetica;
        var fontSize = 24;
        var textFormat = new TextFormat()
        {
            Font = font,
            FontSize = fontSize,
        };

        g.DrawString(text, textFormat, new PointF(100, 100));

        // Create a rectangle
        var rect = new RectangleF(100, 200, 200, 150);
        g.DrawRectangle(rect, Color.Red);

        // Specify the file path where you want to save the PDF
        var filePath = "example.pdf";

        // Save the document to a PDF file
        doc.Save(filePath);

        Console.WriteLine($"PDF created at {filePath}");
    }
}

Explanation of the code

• To represent the PDF document, we construct a new GcPdfDocument object.
• Using doc, add a page to the document.NewPage().
• Make a graphics object (g) to doodle on the page.
• Using g, add text and a rectangle to the page.DrawString() and g.DrawRectangle() are two functions.
• Enter the location to the file where you wish to save the PDF.
• doc Save the document as a PDF file.Save().

After running this code, a PDF file named "example.pdf" will be created in your project directory.

GcPdf Advanced Features
GcPdf has a wide range of tools for creating advanced PDF documents. Here are a few advanced features to look into:

Including Images
Using the g.DrawImage() method, you can add images to your PDF document. This enables you to insert logos, images, or photographs in your documents.

var image = Image.FromFile("logo.png");
g.DrawImage(image, new RectangleF(50, 50, 100, 100));

Making Tables
Tables are widely used to present tabular data in PDF documents. GcPdf includes a Table class that may be used to create tables with a variety of formatting choices.

var table = new Table();
table.DataSource = GetTableData(); // Replace with your data source
page.Elements.Add(table);

Adding Hyperlinks
You can include hyperlinks in your PDFs using the g.DrawString() method with a link destination.
var hyperlinkText = "Visit our website";
var linkDestination = new LinkDestinationURI("https://example.com");
g.DrawString(hyperlinkText, textFormat, new PointF(100, 300), linkDestination);

PDF Security
GcPdf allows you to secure your PDFs by adding passwords or encrypting them. You can set document permissions and control who can view or edit the document.
var options = new PdfSaveOptions
{
    Security = new PdfSecuritySettings
    {
        OwnerPassword = "owner_password",
        UserPassword = "user_password",
        Permissions = PdfPermissions.Print | PdfPermissions.Copy,
    },
};
doc.Save("secure.pdf", options);

Creating customized PDFs for various applications in .NET C# by using GcPdf programmatically is a potent and versatile method. GcPdf offers all the necessary features and flexibility to generate reports, invoices, or other types of documents quickly and efficiently. To enhance your PDF generation capabilities with more in-depth information and examples, please refer to the GcPdf documentation. We wish you happy coding!

After submitting the download link, follow these steps to import the ADCaptcha.dll into an ASP.NET project:

Provide a download link to the ADCaptcha.dll file on your website or any other platform where users can access it.
Include ADCaptcha.dll in the project: After downloading the ADCaptcha.dll, you must include it in the references section of your ASP.NET project.

• In the Solution Explorer of your project, right-click on the "References" node.
• Select "Add Reference."
• Locate the downloaded ADCaptcha.dll file by clicking the "Browse" option.
• Click "Add" to add the ADCaptcha.dll file to the project's references.

Import ADCaptcha Namespace: Import the necessary namespaces into the files where you want to use the ADCaptcha library. For example, if your ADCaptcha.dll has the namespace ADCaptcha, import it in the code files where you use the CAPTCHA functionalities:

using ADCaptcha; // Import the ADCaptcha namespace.

Utilize the ADCaptcha Library: Now that you have imported the ADCaptcha namespace, you can use the CAPTCHA functionalities provided by the ADCaptcha.dll in your code. For example:
using ADCaptcha;

// ... (other code)

// Generate a new CAPTCHA text and image.

string captchaText = CaptchaGenerator.GenerateRandomText(6, DifficultyMode.Medium);

byte[] captchaImageBytes = CaptchaGenerator.GenerateCaptchaImage(captchaText, 200, 60, 30, Color.White, Color.DarkBlue, DistortionTechnique.Warp, DistortionTechnique.NoiseLines);

// ... (other code)

By following these steps, you can successfully import the ADCaptcha.dll into your ASP.NET project and leverage its CAPTCHA generation and verification capabilities to secure your website from automated bots and spam.

How to generate a CAPTCHA image and verify user input
Below are example usages and sample code for the ADCAPTCHA DLL. We will demonstrate how to generate a CAPTCHA image in an ASP.NET web form and how to verify user input against the CAPTCHA text.

Generating and Displaying a CAPTCHA Image (ASP.NET Web Form)
In your ASP.NET web form (e.g., CaptchaPage.aspx), add an Image control to display the CAPTCHA image:

<asp:Image ID="CaptchaImage" runat="server" />
<asp:TextBox ID="UserInputTextBox" runat="server" CssClass="form-control mt-2"></asp:TextBox>
<asp:Button ID="SubmitButton" runat="server" Text="Submit" OnClick="SubmitButton_Click" CssClass="btn btn-info mt-2" />
<%--For Testing Purpose Only DLL By ASHOK DUDI--%>
<asp:Label Text="" ID="lblMsg" runat="server" />

In the code-behind file (CaptchaPage.aspx.cs), add the following code:
using ADCaptcha;

Add the below code to Page_Load event
if (!IsPostBack)
{
    // Generate a new CAPTCHA text (You can also store this in session for verification later).
    string captchaText = CaptchaGenerator.GenerateRandomText(6, DifficultyMode.Medium);

    // Generate the CAPTCHA image and convert it to a base64 string.
    byte[] captchaImageBytes = CaptchaGenerator.GenerateCaptchaImage(captchaText, 200, 60, 24, System.Drawing.Color.White, System.Drawing.Color.DarkBlue,DistortionTechnique.NoiseLines,DistortionTechnique.Swirl, DistortionTechnique.Warp);
    // You can use anyone as required. Generate the CAPTCHA image and convert it to a base64 string.
    //byte[] captchaImageBytes = CaptchaGenerator.GenerateCaptchaImage(captchaText, 200, 60);
    string captchaImageBase64 = Convert.ToBase64String(captchaImageBytes);

    // Set the CAPTCHA image source to the base64 string.
    CaptchaImage.ImageUrl = "data:image/png;base64," + captchaImageBase64;
    CaptchaImage.BorderColor = System.Drawing.Color.DarkBlue;
    CaptchaImage.BorderWidth = 1;

    // Store the CAPTCHA text in a session for verification during form submission.
    Session["CaptchaText"] = captchaText;
}

To verify Captcha, use the below code on SubmitButton_Click event
protected void SubmitButton_Click(object sender, EventArgs e)
{
    lblMsg.Text = "";
    // Retrieve the stored CAPTCHA text from the session.
    string captchaText = Session["CaptchaText"] as string;

    // Retrieve the user's input from the TextBox.
    string userInput = UserInputTextBox.Text;

    // Verify the user's input against the CAPTCHA text (case-insensitive comparison by default).
    bool isCaptchaValid = CaptchaVerifier.VerifyCaptcha(captchaText, userInput,false);

    if (isCaptchaValid)
    {
        // CAPTCHA verification successful.
        // Proceed with the form submission or any other action.
        // ...
        lblMsg.Text = "Success";
        // Optionally, you can remove the CAPTCHA text from the session to prevent reuse of the same CAPTCHA.
       Session.Remove("CaptchaText");
    }
    else
    {
        lblMsg.Text = "Failed";
        // CAPTCHA verification failed.
        // Show an error message to the user and ask them to try again.
        // ...
    }
}

Remember to modify the code and styling to match the structure and design of your unique ASP.NET project. Additionally, ensure that the session state in your ASP.NET application is appropriately configured to save and retrieve the CAPTC. Remember to alter the code and styling to reflect your individual ASP.NET project structure and design. Additionally, check that the session state in your ASP.NET application is appropriately configured to save and retrieve the CAPTCHA text for verification.Text from HA for verification.

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