Separating Business Model and Logic Ensuring SRP in Car Class Design

In software architecture, adhering to the Single Responsibility Principle (SRP) is crucial to maintaining clean, modular, and maintainable code. One common mistake is merging business models with business logic, leading to unnecessary dependencies and reduced scalability. This article explores how to properly separate these concerns using an MVC-based approach for a Car class and its related components.

Issue: Business Model Breaking SRP

A Car class should represent a data model rather than handle business logic or external service interactions. However, integrating dependencies like IFileSystemService into the Car class blurs the lines between the model and the business logic, leading to tightly coupled code that is harder to maintain and extend.

Proposed Solution: Layered Architecture

To enforce SRP, we should implement a layered structure where each component has a distinct responsibility. The following diagram illustrates the appropriate separation of concerns:

flowchart TD
CarController --> CarService
CarService --> ImageService
ImageService --> Image
CarService --> CarRepository
CarRepository --> Car
CarService --- Info(Gives controller
a model that
includes an
image and 
a car)

Responsibilities of Each Component:

1. CarController: Only interacts with CarService, ensuring that it remains unaware of implementation details.
2. CarService: Puts all necessary data together (e.g., fetching a Car model and its corresponding image).
3. CarRepository: Handles Car data persistence.
4. ImageService: Manages image-related operations separately from the Car model.
5. Image: Represents an image as a distinct model, ensuring separation from Car.

Improving Method Naming for Clarity

Several method names in the current design suggest unclear responsibilities:

Incorrect Naming Conventions:

1

public Car GetPictureForCar(int carId);

• Issue: The method name implies it returns an image, but it returns a Car.
• Expected Fix: Return an Image object instead.

1

Car myCar = this.GetFileForCar(carId);

• Issue: A method that suggests retrieving a file should not return a Car.
• Expected Fix: It should return either a File object or a string representing the file name.

1

Image imgfile = _Repository.GetPhysicalFileLocation(carId);

• Issue: A method named GetPhysicalFileLocation should return a string, not an Image.
• Expected Fix: Rename or refactor to return a string file path.

Naming Conventions and Private Field Formatting

• In C#, private fields should use camelCase:

1

private readonly IRepository _repository;

• Correcting _Repository to _repository follows standard C# naming conventions.

Conclusion

By ensuring that the Car class remains a pure model and delegating responsibilities to appropriate services, we achieve a cleaner and more maintainable architecture. The CarService acts as the intermediary, orchestrating data retrieval and transformation without violating SRP. Implementing clear method names further enhances readability and predictability, making the system easier to understand and extend.