Single Responsibility Principle (SRP)

h2>Definition

A class should have only one responsibility or one reason to change.
👉 One class = One job.

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Purpose

• Keep classes focused
• Reduce complexity
• Improve maintainability
• Make code easier to test
• Avoid tightly coupled logic

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Bad Example ❌

public class InvoiceService
{
    public void CreateInvoice()
    {
        Console.WriteLine("Invoice Created");
    }

    public void SaveToDatabase()
    {
        Console.WriteLine("Saved to DB");
    }

    public void SendEmail()
    {
        Console.WriteLine("Email Sent");
    }
}

Problem

This class handles:

• Invoice creation
• Database operations
• Email sending

👉 Multiple responsibilities.

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Good Example ✅

Invoice Logic

public class InvoiceService
{
    public void CreateInvoice()
    {
        Console.WriteLine("Invoice Created");
    }
}

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Database Logic

public class InvoiceRepository
{
    public void Save()
    {
        Console.WriteLine("Saved to DB");
    }
}

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Email Logic

public class EmailService
{
    public void Send()
    {
        Console.WriteLine("Email Sent");
    }
}

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Key Concept

Instead of:

One class doing everything

We do:

Separate focused classes

👉 Easier to manage and extend.

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Real-Time Scenario

Invoice System:

• InvoiceService → invoice logic
• InvoiceRepository → database logic
• EmailService → notifications

👉 Each class has single responsibility.

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Advantages

• ✔ Easier maintenance
• ✔ Better readability
• ✔ Easier unit testing
• ✔ Reduced side effects
• ✔ Better scalability

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Disadvantages

• ✖ More classes/files
• ✖ Slightly increased structure complexity

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When to Use

Use SRP when:

• Class has multiple responsibilities
• Business logic becomes large
• Different changes happen frequently
• Code becomes difficult to maintain

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Real Project Mapping (.NET + Angular)

Layer	Responsibility
Controller	Handle HTTP requests
Service	Business logic
Repository	Database operations
EmailService	Notifications
LoggerService	Logging

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ASP.NET Core Real Example

Controller → Request Handling
Service → Business Logic
Repository → Data Access

👉 SRP everywhere in Clean Architecture.

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SRP vs Separation of Concerns

SRP	Separation of Concerns
Class-level principle	System-level principle
One class = one job	Divide application into sections

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Pro Tip

SRP works best with:

• Clean Architecture
• Repository Pattern
• Dependency Injection
• Microservices

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Summary

SRP helps you:

• Keep classes focused
• Reduce complexity
• Improve maintainability

👉 Perfect for:

• Enterprise applications
• APIs
• Microservices
• Large-scale projects