Make Your Object Model More Object-Oriented

Summary

This video demonstrates how to refactor an anemic domain model into a clean, object-oriented design for modeling the publication status of books. It highlights the pitfalls of the initial design, emphasizing issues like inconsistency and complexity. By introducing abstraction through interfaces and removing redundant logic, the refactored model is simplified. The video also incorporates functional design principles, such as higher-order functions for handling nullable dates, ensuring more predictable and maintainable code. The final design offers modularity, clear separation of concerns, and greater extensibility, making the system easier to manage and evolve.

Takeaways

• 😀 Start from the bottom-up when transitioning from an anemic domain model to an object-oriented model, with smaller objects evolving into larger ones.
• 😀 Avoid clever programming tricks that introduce complexity and lead to fragile code. A more straightforward and predictable design is preferable.
• 😀 When modeling complex objects, it's crucial to acknowledge the distinct states they can represent, such as a date, a month, or a year, to create proper abstractions.
• 😀 Using an abstract class can represent multiple variants of the same concept, but when there is no shared behavior, an interface is more appropriate.
• 😀 Interfaces should declare the common operations, with default implementations for shared behavior that can be overridden when needed.
• 😀 Simplicity in design is key. Every operation should have one way to function, making the code easier to understand and maintain.
• 😀 Avoid nullable references for optional properties. Instead, use a method that either maps the contained value or returns a substitute, ensuring consistency and reducing branching.
• 😀 Use functional programming principles, such as higher-order functions, to make the design more flexible while avoiding null-related branching.
• 😀 Inheritance should be used only when there is shared behavior across classes. Otherwise, interfaces provide a cleaner and more extendable solution.
• 😀 Separate concerns by delegating responsibilities to specific objects. For example, sorting operations can be handled by objects that encapsulate sorting logic, keeping the application code clean and focused.
• 😀 Proper object-oriented design focuses on behavior over state, allowing features to evolve independently without breaking the core structure of the application.

Q & A

What is the primary issue with the initial book publication status class design?

The main issue is that the class doesn't model the publication state in a meaningful, object-oriented way. It uses a combination of nullable objects and Boolean flags, which leads to confusion and lack of clarity in representing the publication state of a book.

How does the script suggest transforming an anemic domain model into an object-oriented one?

The script suggests starting from the smallest, most basic objects and gradually building them into larger ones, ensuring that each object has a clear responsibility and behaves consistently.

Why is the design of the 'Date' class considered flawed in the original implementation?

The 'Date' class is flawed because it relies on multiple Boolean flags and static factory methods to represent incomplete or unclear date information, which complicates the logic and leads to unpredictable behavior.

What is the significance of introducing abstract classes and interfaces in the redesign?

The introduction of abstract classes and interfaces helps clearly define the different variations of the publication state (e.g., full date, year-month, year) while avoiding unnecessary inheritance and enabling better extensibility and maintainability.

How does the script propose handling the nullable date scenario?

Instead of using nullable references and causing branching in the code, the script suggests using higher-order functions like 'Map' to optionally transform the date, providing a more predictable behavior and avoiding null checks.

What role do higher-order functions play in the redesign?

Higher-order functions, like the 'Map' method, are used to transform or act on the date if available, allowing the caller to supply a substitute date when necessary. This approach reduces complexity and ensures consistent behavior even when no date is assigned.

Why does the script emphasize the importance of avoiding 'clever tricks' in code?

Clever tricks can lead to complex, hard-to-maintain code that is difficult to extend or debug. The script stresses using clear, consistent design principles to ensure long-term maintainability and prevent future technical debt.

What is the 'next date' calculation, and why is it tricky in the original design?

The 'next date' calculation is problematic because it requires handling multiple date formats (e.g., full date, month, year), and the original design used multiple checks and flags to determine how to calculate the next valid date, making the code complex and error-prone.

How does the final design separate concerns for better maintainability?

The final design separates concerns by delegating date calculations and publication status handling to distinct classes or interfaces, ensuring that each component has a clear responsibility and that the code remains modular and easier to maintain.

What does the script suggest regarding database schema changes when refactoring the design?

The script points out that even though the design has changed significantly (from nullable references to interfaces), the underlying database schema remains unaffected, highlighting the benefit of keeping the database structure separate from the object model.