Master Software Architecture: Module 5 – Object-Oriented Architecture | Complete Guide with C#, ASP.NET & SQL Server

 

📑 Table of Contents

1. Introduction to Object-Oriented Architecture

2. OOP Principles at the Architectural Level
   2.1 Encapsulation in Architecture
   2.2 Inheritance & Reusability
   2.3 Polymorphism in Large Systems
   2.4 Abstraction & Interfaces
   2.5 Example: ASP.NET ERP Module Design

3. Designing Reusable Components
   3.1 Componentization Concepts
   3.2 Reusable Business Services
   3.3 Example: Inventory & Billing Components in ERP
   3.4 Best Practices

4. Interfaces, Abstractions & Dependency Inversion
   4.1 Why Dependency Inversion?
   4.2 Using Interfaces in C#
   4.3 ASP.NET Dependency Injection Example
   4.4 Pros, Cons & Alternatives

5. Component Coupling & Cohesion
   5.1 Types of Coupling (Tight, Loose)
   5.2 High Cohesion Principle
   5.3 Example: Invoice & Payment Services
   5.4 Best Practices & Pitfalls

6. Design Patterns Overview
   6.1 Creational Patterns (Factory, Singleton, Builder)
   6.2 Structural Patterns (Adapter, Composite, Facade)
   6.3 Behavioral Patterns (Observer, Strategy, Command)
   6.4 Examples in C#, ASP.NET, SQL Server
   6.5 Choosing the Right Pattern

7. Real-Life ERP Case Study
   7.1 Sales Order & Invoice Workflow
   7.2 Applying OOP & Patterns in ERP
   7.3 Component Interaction with SQL Server

8. Best Practices in Object-Oriented Architecture
   8.1 Applying SOLID Principles
   8.2 Error Handling & Logging
   8.3 Security & Performance Considerations

9. Pros, Cons & Alternatives
   9.1 OOP vs Functional Programming
   9.2 OOP vs Procedural Approach
   9.3 Alternatives like Microservices, Event-Driven Design

10. Conclusion & Key Takeaways

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1. Introduction to Object-Oriented Architecture

Object-Oriented Architecture is not just coding with classes — it’s about designing enterprise-level applications using OOP principles.

Real-life Example:

• An ERP system has modules like Sales, Purchase, Inventory, and Accounts.

• If each is designed as an object-oriented component, they can evolve independently, scale, and integrate easily.

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2. OOP Principles at the Architectural Level

2.1 Encapsulation in Architecture

Encapsulation hides internal details of components.

Example: SQL Server + C# Encapsulation

public class OrderRepository
{
    private readonly string _connectionString;
    public OrderRepository(string connectionString)
    {
        _connectionString = connectionString;
    }

    public void SaveOrder(Order order)
    {
        using(SqlConnection conn = new SqlConnection(_connectionString))
        {
            conn.Open();
            SqlCommand cmd = new SqlCommand("sp_SaveOrder", conn);
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.AddWithValue("@CustomerId", order.CustomerId);
            cmd.Parameters.AddWithValue("@Amount", order.Amount);
            cmd.ExecuteNonQuery();
        }
    }
}

👉 Business logic doesn’t know SQL details — only OrderRepository handles it.

2.2 Inheritance & Reusability

public abstract class Payment
{
    public abstract void ProcessPayment(decimal amount);
}

public class CreditCardPayment : Payment
{
    public override void ProcessPayment(decimal amount)
    {
        Console.WriteLine($"Processing credit card payment of {amount}");
    }
}

public class PayPalPayment : Payment
{
    public override void ProcessPayment(decimal amount)
    {
        Console.WriteLine($"Processing PayPal payment of {amount}");
    }
}

ERP Benefit: Easily add new payment methods without modifying existing code.

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3. Designing Reusable Components

Reusable components reduce duplication and maintenance effort.

Example – ASP.NET Core Service Layer

public interface IInvoiceService
{
    void GenerateInvoice(int orderId);
}

public class InvoiceService : IInvoiceService
{
    public void GenerateInvoice(int orderId)
    {
        // Fetch order from DB and generate invoice
    }
}

This InvoiceService can be reused across Sales, Returns, or Subscription modules.

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4. Interfaces, Abstractions & Dependency Inversion

Dependency Inversion ensures high-level modules don’t depend on low-level modules, but on abstractions.

ASP.NET Core Dependency Injection Example

public void ConfigureServices(IServiceCollection services)
{
    services.AddScoped<IInvoiceService, InvoiceService>();
    services.AddScoped<IPaymentService, PaymentService>();
}

👉 Business logic depends on interfaces, not implementations.

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5. Component Coupling & Cohesion

• Loose Coupling = Easier maintenance.

• High Cohesion = Each module has a single responsibility.

Bad Example (Tight Coupling):

public class InvoiceManager
{
    private PaymentService _paymentService = new PaymentService();
}

Good Example (Loose Coupling via Interface):

public class InvoiceManager
{
    private readonly IPaymentService _paymentService;
    public InvoiceManager(IPaymentService paymentService)
    {
        _paymentService = paymentService;
    }
}

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6. Design Patterns Overview

6.1 Creational – Factory Pattern

public static class PaymentFactory
{
    public static Payment CreatePayment(string type)
    {
        return type switch
        {
            "CreditCard" => new CreditCardPayment(),
            "PayPal" => new PayPalPayment(),
            _ => throw new NotImplementedException()
        };
    }
}

6.2 Structural – Facade Pattern

public class OrderFacade
{
    private readonly IOrderService _orderService;
    private readonly IInvoiceService _invoiceService;
    public OrderFacade(IOrderService orderService, IInvoiceService invoiceService)
    {
        _orderService = orderService;
        _invoiceService = invoiceService;
    }

    public void PlaceOrder(Order order)
    {
        _orderService.Save(order);
        _invoiceService.GenerateInvoice(order.OrderId);
    }
}

6.3 Behavioral – Strategy Pattern

public interface IDiscountStrategy
{
    decimal ApplyDiscount(decimal amount);
}

public class PercentageDiscount : IDiscountStrategy
{
    public decimal ApplyDiscount(decimal amount) => amount * 0.9M;
}

ERP Benefit: Choose different discount strategies dynamically.

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7. Real-Life ERP Case Study

👉 Sales Order → Invoice → Payment

• OOP Principles keep modules separate

• Patterns allow flexible design

• SQL Server ensures reliable data

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8. Best Practices

• Apply SOLID principles

• Log exceptions (Serilog, NLog)

• Secure sensitive data (Encryption)

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9. Pros, Cons & Alternatives

• OOP Pros: Reusability, maintainability, abstraction

• Cons: Over-engineering risk, performance overhead

• Alternatives: Functional Programming, Microservices

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10. Conclusion

Object-Oriented Architecture transforms software into scalable, maintainable, enterprise-ready applications. By mastering OOP principles, reusable components, dependency inversion, coupling/cohesion, and design patterns, you can architect solutions that evolve with business needs.

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