The SOLID Principles are the design principles that enable us to manage several software design problems. These principles provide us with ways to move from tightly coupled code to loosely coupled and encapsulated real business needs properly. Also readable, adaptable, and scalable code.
The SOLID Principles guide developers as they write readable, adaptable, and scalable code or design an application.
The SOLID Principles can be applied to any OOP program.
The SOLID Principles were developed by computer science instructor and author Robert C. Martin.
Now, the SOLID Principles have also been adopted in both agile development and adaptive software development.
The 5 principles of SOLID are:
1. Single Responsibility Principle (SRP)
2. Open-Closed Principle (OCP)
3. Liskov Substitution Principle (LSP)
4. Interface Segregation Principle (ISP)
5. Dependency Inversion Principle (DIP)
Single Responsibility Principle (SRP) is one of the SOLID principles that states a class, module, or function should have only one reason to change.
Implementation:
Let us look at an example of how SRP can be applied to make our EmployeeService class more readable.
// Does not follow a Single-responsibility principle (SRP)
public class EmployeeService
{
public void Register(string eployeename)
{
//Employee name restrictions
if (eployeename == "admin")
throw new InvalidOperationException();
//Insert employee into database.
SqlConnection connection = new SqlConnection();
connection.Open();
SqlCommand command = new SqlCommand("INSERT INTO [...]");
//Send a welcome email to employee.
SmtpClient client = new SmtpClient("smtp.emailhost.com");
client.Send(new MailMessage());
}
}
The program above does not follow the Single-responsibility principle (SRP) because EmployeeService does three different jobs:
1. Register an employee,
2. Connect to the database to insert the employee’s name
3. Send a welcome email to the employee
This type of class would create confusion in larger projects because all the above 3 features are in the same class. So, we need to split the class into three specific classes that will do a single job.
Now all other jobs refactored to separate classes
1. EmployeeService class
2. EmployeeRepository class
3. EmailService class
The code looks like this,
public class EmployeeService
{
public void Register (string eployeename)
{
//Employee name restrictions
if (eployeename == "admin")
throw new InvalidOperationException();
//Insert employee into database.
_userRepository.Insert(...);
//Send a welcome email to employee.
_emailService.Send(...);
}
}
This achieves the SRP because EmployeeService only registers an employee and the only reason it would change is if more eployeename restrictions were added. All other behaviors are maintained in the program but are now achieved with calls to EmployeeRepository and EmailService.
Advantages of the Single Responsibility Principle:
1. Increased Code Reusability
2. Reduce code Complexity
3. Clearer Design
4. Easier Testing
5. Enhanced Readability and Maintainability
6. Clearer Design
Disadvantages of the Single Responsibility Principle:
1. Increased the Number of Classes: SRP may lead to a larger number of smaller classes, each responsible for a specific task. This can sometimes make the codebase feel more fragmented and complex.
2. Potential Overhead: Breaking down responsibilities into small, focused classes might introduce some overhead.
When to use the Single Responsibility Principle:
Remember, the goal is to design classes that are focused on a single responsibility. When a class has multiple reasons to change, it becomes more difficult to maintain, test, and understand. Applying SRP leads to more modular, maintainable, and flexible code.
