Structural Design Patterns (C# / .NET)

What are Structural Patterns?

Structural patterns focus on how classes and objects are organized and connected. They help simplify relationships between objects and create flexible system structures.

Purpose of Structural Patterns

  • Simplify complex structures
  • Improve code organization
  • Reduce tight coupling
  • Increase flexibility and reusability
  • Help integrate incompatible systems

Types of Structural Patterns

Pattern Purpose Real-Time Example
Adapter Convert one interface into another Third-party payment API
Decorator Add behavior dynamically Logging, Discount
Facade Simplify complex system Order workflow
Composite Handle tree-like structures Invoice items, Folder
Proxy Control access to object Lazy loading, Security
Bridge Separate abstraction from implementation Notification systems
Flyweight Reduce memory usage Shared object caching

1. Adapter Pattern

Idea

Convert incompatible interfaces into compatible ones.

Real Scenario

Integrating third-party APIs.

Example Use Cases

  • Payment gateway integration
  • Legacy system support
  • External service adapters

2. Decorator Pattern

Idea

Add extra functionality without modifying original class.

Real Scenario

Adding:

  • Logging
  • Discount
  • Validation

Example Use Cases

  • Middleware pipeline
  • Pricing systems
  • Feature extensions

3. Facade Pattern

Idea

Provide one simple interface to a complex system.

Real Scenario

Single method:

PlaceOrder()

Internally:

  • Create order
  • Process payment
  • Send notification

Example Use Cases

  • Service orchestration
  • API gateways
  • Workflow handling

4. Composite Pattern

Idea

Treat individual and grouped objects the same.

Real Scenario

  • Invoice with multiple items
  • Folder with files/subfolders

Example Use Cases

  • Tree structures
  • Menu systems
  • Shopping carts

5. Proxy Pattern

Idea

Control access to another object.

Real Scenario

  • Lazy loading images
  • Authentication check before access

Simple Example

public interface IImage
{
    void Display();
}

public class RealImage : IImage
{
    public void Display()
    {
        Console.WriteLine("Displaying image");
    }
}

public class ProxyImage : IImage
{
    private RealImage _realImage;

    public void Display()
    {
        if (_realImage == null)
            _realImage = new RealImage();

        _realImage.Display();
    }
}

6. Bridge Pattern

Idea

Separate abstraction from implementation.

Real Scenario

Notification system:

  • SMS
  • Email
  • Push notification

Example Use Cases

  • Multi-platform systems
  • Device abstraction
  • Notification providers

7. Flyweight Pattern

Idea

Reuse shared objects to reduce memory usage.

Real Scenario

Thousands of repeated icons/images.

Example Use Cases

  • Caching systems
  • Game development
  • UI rendering systems

Advantages of Structural Patterns

  • ✔ Better architecture
  • ✔ Reusable components
  • ✔ Easier maintenance
  • ✔ Flexible relationships
  • ✔ Reduced complexity

Disadvantages

  • ✖ More abstraction layers
  • ✖ Increased number of classes
  • ✖ Learning complexity
  • ✖ Over-engineering risk

When to Use Structural Patterns

  • When system structure becomes complex
  • When integrating external systems
  • When adding features dynamically
  • When managing hierarchical data
  • When simplifying multiple services

Real Project Mapping (.NET + Angular)

Feature Structural Pattern
Payment Gateway Adapter
Middleware Decorator
Order Processing Facade
Invoice Items Composite
Authentication Proxy Proxy
Notification Providers Bridge
Cache / Shared Resources Flyweight

Summary

Structural patterns help:

  • Organize classes effectively
  • Simplify object relationships
  • Build scalable architectures

👉 Perfect for enterprise-level .NET Core + Angular applications.

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