Design Patterns vs SOLID Principles:

What Software Engineers Should Actually Learn First

A lot of software engineers have heard about design patterns — Factory, Strategy, Observer, Singleton, etc. Some have even used them in production code.

But here’s the thing:

Many developers jump into design patterns too early, and end up writing code that looks “advanced” but is harder to maintain.

On the other hand, some engineers focus only on SOLID principles and think design patterns are optional or outdated.

In reality, SOLID principles and design patterns are not competing ideas.

They solve different problems:

• SOLID principles help you design code correctly.
• Design patterns give you reusable structures for common design problems.

This post breaks down the difference in a practical way and answers the real question:

What should software engineers actually learn first — SOLID or design patterns?

 

Table of Contents

What Are SOLID Principles?

What Are Design Patterns?

SOLID vs Design Patterns (The Real Difference)

What Should You Learn First?

Practical Examples: SOLID → Pattern

• Example: Strategy Pattern from Open/Closed Principle

When Design Patterns Become a Problem

How SOLID + Patterns Improve AI Code Prompts

Conclusion

References

What Are SOLID Principles?

SOLID is a set of five principles that help engineers write code that is:

• Clean
• Scalable
• Testable
• Easy to maintain

SOLID is not about writing more code. It’s about writing code that can survive growth.

SOLID stands for:

1) S — Single Responsibility Principle (SRP)

A class/module should have one reason to change.

Meaning:

Don’t put 10 different responsibilities inside one class just because it “works”.

 

2) O — Open/Closed Principle (OCP)

Software entities should be:

• Open for extension
• Closed for modification
  

Meaning:

You should be able to add new behaviour without rewriting old code.

3) L — Liskov Substitution Principle (LSP)

Subclasses should be substitutable for their base classes without breaking the system.

Meaning:

If B extends A, you should be able to use B anywhere A is expected without surprises.

4) I — Interface Segregation Principle (ISP)

Clients should not be forced to depend on interfaces they don’t use.

Meaning:

Don’t build one massive interface and force everyone to implement unnecessary methods.

5) D — Dependency Inversion Principle (DIP)

High-level modules should not depend on low-level modules. Both should depend on abstractions.

Meaning:

Your core business logic shouldn’t be tightly coupled to external services like payment gateways, SMS providers, database engines, etc.

What Are Design Patterns?

Design patterns are typical solutions to commonly repeated software design problems.

They are like pre-made blueprints that you can customize to solve recurring design problems in your codebase.

They are usually categorized into:

• Creational patterns (object creation)
• Structural patterns (object composition)
• Behavioural patterns (communication/behaviour)

SOLID vs Design Patterns (The Real Difference)

This is the simplest way to understand it:

SOLID = principles (how to think)
Design patterns = patterns (how to structure)

Another way:

• SOLID teaches you good design habits
  
• Design patterns are ready-to-use tools that appear when applying SOLID

Key difference

Feature	SOLID Principles	Design Patterns
Type	Guidelines	Reusable solutions
Focus	Code quality, maintainability	Structure and common architecture
Goal	Prevent bad design	Solve recurring design problems
Output	Clean architecture decisions	Implementable template
Usage	Always	Only when needed

What Should You Learn First?

If you’re asking what to learn first, my honest answer is:

Learn SOLID first. Then learn design patterns.

Here’s why:

• SOLID helps you know when a pattern is necessary
  
• SOLID helps you avoid overengineering
  
• SOLID makes patterns easier to understand and apply correctly

Design patterns without SOLID is like:

having a toolbox but no understanding of construction.

You will use tools incorrectly.

Practical Examples: SOLID → Pattern

This is where it gets interesting. In real software, patterns often appear naturally when you apply SOLID.

Example : Strategy Pattern from Open/Closed Principle

Problem

You are building a payment system:

• Card
• Transfer
• USSD
• Wallet

Beginner implementation:

async function pay(method: string, amount: number) {

    if (method === “card”) {

       return payWithCard(amount);

    }

    if (method === “transfer”) {

        return payWithTransfer(amount);

    }

    if (method === “ussd”) {

        return payWithUssd(amount);

    }

    throw new Error(“Unsupported method”);

}

This works but violates OCP.

Because every time a new payment method is added, you modify this function.

SOLID thinking

OCP says:

Extend behaviour without modifying existing logic.

Solution (Strategy Pattern)

interface PaymentStrategy {

    pay(amount: number): Promise<void>;

}

class CardPayment implements PaymentStrategy {

    async pay(amount: number) {

        // card logic

    }

}

class TransferPayment implements PaymentStrategy {

    async pay(amount: number) {

        // transfer logic

    }

}

class PaymentService {

    constructor(private strategy: PaymentStrategy) {}

    pay(amount: number) {

        return this.strategy.pay(amount);

    }

}

Now adding a new method means:

• create a new class
• no modification to core logic

That’s OCP in action — and Strategy pattern is the result.

When Design Patterns Become a Problem

This is where many engineers get it wrong.

Design patterns become a problem when:

• You force them into small projects
• You add abstraction “just in case”
• Your code becomes harder to read than it needs to be
• You end up with 20 files for a feature that needs 3 files

A simple rule:

If the pattern doesn’t reduce complexity, don’t use it.

 

How SOLID + Patterns Improve AI Code Prompts

This is one of the most practical benefits today.

Most AI prompts fail because they ask for code without specifying:

• Architecture
• Boundaries
• Extensibility
• Testability

Weak prompt ❌

“Build a payment module for card and transfer.”

You’ll likely get:

• big if/else
• tight coupling
• poor structure

Better prompt with SOLID + pattern guidance ✅

“Build a payment module following SOLID principles.
Use Strategy pattern for payment methods.
Use a Factory for selecting strategy.
Ensure PaymentService is open for extension and closed for modification.
Include unit-test friendly structure and interfaces.”

Now the AI is guided to produce:

• modular code
• better separation
• extensibility
• testability

Conclusion

SOLID principles and design patterns are not rivals.

They work together:

• SOLID teaches you how to think about clean design
  
• Design patterns give you practical templates to apply that thinking
  

If you’re choosing what to learn first:

Learn SOLID first.
Then learn patterns.

Because patterns are easier to apply correctly when you understand the principles behind them.

References

1. Gamma, E., Helm, R., Johnson, R., Vlissides, J. — Design Patterns: Elements of Reusable Object-Oriented Software (GoF), Addison-Wesley, 1994.
2. Refactoring.Guru — Design Patterns
   https://refactoring.guru/design-patterns
3. Robert C. Martin — Agile Software Development, Principles, Patterns, and Practices
4. Robert C. Martin — Clean Architecture: A Craftsman’s Guide to Software Structure and Design
5. Martin Fowler — Patterns of Enterprise Application Architecture
   https://martinfowler.com/books/eaa.html