Save Your Backend: Separating Business Logic and Data Access in Your API

If you’re maintaining a backend API in your software application, your black box goal is simple: provide efficient access and processing of data per your client’s requests. Maintaining that goal as your application grows, however, becomes increasingly difficult. More endpoints need to be exposed. Business logic grows in complexity, data needs to be wrangled into different formats, and more entities/models come into the picture. What can we do now to alleviate our future backend aches and pains?

I may not have all the answers, but there’s one design pattern with the potential to save you some ibuprofen: maintaining the separation of concerns between business logic and data access functions. Adhering to this principle not only keeps your code cleaner and more organized as your API grows but also offers other benefits crucial for long-term success.

(Now would be a great time to play “Gotta Keep ‘Em Separated,” Alexa.)

The Great Divide: Critical Business Logic vs. Simple CRUD Operations

As you’re building your API, you’ll write sets of functions to handle data per entity (aka model or domain type, represented by database tables). The key to this design pattern is distinguishing between core data processing functions and the handling of data access and storage. You’re separating the business logic (aka “service” functions), which happen to be more complex and sensitive, from CRUD operations (aka “repository” functions), which tend to be pretty dumb. (It says nothing about your character CRUD. You’re still so important!)

By keeping these two types of functions distinct, you can separate these entity functions into different modules or classes, and effectively create separate layers in your API with specific responsibilities. This clean layer separation ensures that data access code doesn’t clutter up your critical business logic. It also can allow you to assert that only “repository” classes or modules can maintain a connection to the database. It also makes your code more readable, maintainable, and adaptable in the process. 

Unit Testing

Unit testing is a fundamental practice for maintaining bug-free code (and your peace of mind). When you separate your business logic from data access, you can write unit tests specifically aimed at the business logic, focusing on the functions critical for your application’s success. This leaves your CRUD operations to be easily mocked or stubbed out. That way, you can thoroughly test your service functions without the distraction of the intricacies of database access.

Reducing the Need for Future Refactors

Starting your project with a well-structured separation of business logic and data access layers pays off in the long run. It prevents your codebase from turning into a rat’s nest of intertwined logic and data access. A single-module hot mess express is not only challenging to work with but can also be a breeding ground for bugs. By adhering to this separation early on, you reduce the need for time-consuming and error-prone refactoring in the future.

Generic Classes for Data Access

Separating data access into its own layer allows for the potential to create reusable and generic classes for your CRUD operations. You can leverage these generic classes or repositories as you need to create new entities, promoting code reusability. This not only saves a ton of development time but also ensures consistency and confidence in your data access functions across the board.

Lower Probability of Cyclical Dependencies

One of the most challenging problems in a growing API can be managing cyclical dependencies. In that case, modules or classes depend on each other in a never-ending loop of horror and create an impossible request context state. Introducing one of these dependency cycles can suddenly turn an error-free back-end dream into an API nightmare.

You need to unnest the dependencies, refactor, and re-test to break the cycle. By separating business logic and data access functions into separate modules, you reduce the likelihood of creating these dependency loops, and enhance the flexibility of your API in handling new context situations.

So, maybe you did start your project by throwing each entity’s related functions into a single class and calling it a day. There’s still hope: adopting this separation pattern now for each new entity you introduce is still better than nothing, and you can always go back and refactor the old stuff as time goes on. You’ll foster clean code, enable more focused unit testing, prevent future refactoring headaches, promote code reusability, and minimize the risk of cyclical dependencies. Sow the seeds of API layer separation in your project. Then, you’ll reap the sweet fruits of less backend stress in the future.


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