Describe a scenario where you would choose to handle error conditions in the Data Layer versus the Domain Layer in Clean Architecture. Justify your reasoning for each scenario.
Android interview question for Advanced practice.
Answer
The choice of where to handle error conditions depends on the type of error. Data Layer Error Handling: The Data layer is the appropriate place to handle errors that are specific to the data source and can be resolved within that layer. The goal is to shield the rest of the app from data-source-specific problems. Scenario: A network request fails due to a SocketTimeoutException. The repository in the Data layer could catch this exception and automatically retry the request a few times. If all retries fail, it could then decide to load data from a local cache instead. Justification: The Domain layer doesn't need to know about network timeouts or retry logic. It just needs the data. By handling this in the Data layer, the logic is encapsulated where it belongs, and the Domain layer remains clean. Domain Layer Error Handling: The Domain layer should handle errors that represent a failure of a business rule or use case, which the UI needs to be aware of. Scenario: A user tries to register with a username that is already taken. The RegisterUserUseCase in the Domain layer would call the repository to save the new user. The repository's implementation attempts to insert into the database and gets a UniqueConstraintException. The repository should map this low-level exception to a more domain-specific error, like UsernameAlreadyExistsException. Justification: The RegisterUserUseCase catches this specific exception. This is not a data source issue to be hidden, but a business rule violation. The use case then returns a Result.Failure(UsernameAlreadyExists) to the ViewModel, which can then display an appropriate error message to the user.
Explanation
Proper error handling is critical for a robust and user-friendly application.