Where Should Complex Query Conditions Live: Data Mapper or Service Layer?

Should the Data Mapper or Service Layer Handle Complex Query Conditions?

This question arises in the context of complex queries involving multiple conditions. The Data Mapper pattern, designed to facilitate database interactions, typically provides a generic get() method for retrieving data based on specified conditions. However, in scenarios where more intricate queries are required, concerns arise regarding the appropriate handling of these conditions.

One approach involves extending the get() method of the Data Mapper to accept multiple conditions. This allows the service layer to call the extended method directly, reducing its role to a mere intermediary. Conversely, the alternative approach empowers the service layer to parse the conditions before invoking the generic get() method with multiple conditions passed. This shifts the conditional logic to the service layer, leaving the Data Mapper with a simpler implementation.

While the service layer approach ensures containment of domain logic within the model layer, it arguably compromises the primary purpose of the Data Mapper pattern, which is to handle database interactions. Some argue that the mapper should be kept simple, focusing on data retrieval and storage, while the service layer assumes responsibility for managing complex queries and ensuring adherence to business rules.

Alternatively, the Data Mapper approach maintains the separation of concerns, with the mapper handling data manipulation and the service layer responsible for higher-level tasks. The mapper can be extended to include methods tailored to handle specific combinations of conditions, such as getByAuthorAndPublisher(). This approach reduces the service layer's role to a coordinator, delegating much of the conditional logic to the domain objects themselves.

Ultimately, the choice between these approaches depends on factors such as the complexity of the application, the desired level of granularity in data retrieval, and the team's preferences. There is no universally accepted solution, but understanding the trade-offs and considering the context of the application will help developers determine the most appropriate approach for their specific use case.

The above is the detailed content of Where Should Complex Query Conditions Live: Data Mapper or Service Layer?. For more information, please follow other related articles on the PHP Chinese website!