Data Mapper vs. Service Layer: Who Should Handle Conditions in Complex Queries?

Handling Conditions in Complex Queries: Data Mapper vs. Service Layer

When constructing complex queries, the question arises as to whether the data mapper or the service layer should manage the conditions. This conundrum stems from the desire to strike a balance between simplicity and maintainability.

Data Mapper Approach

The data mapper pattern advocates for a minimalist interface, with methods like fetch(), save(), and remove() handling basic operations. Conditions are encapsulated within the domain object itself, ensuring a clean data mapper interface.

$user = new User;
$user->setName('Jedediah');

$mapper = new UserMapper;
$mapper->fetch($user);

if ($user->getFlags() > 5) {
    $user->setStatus(User::STATUS_LOCKED);
}

$mapper->save($user);

This approach ensures that the data mapper remains focused on its core functionality, while also facilitating complex query conditions through the domain object. However, it requires a public method for retrieving data from the domain object for fetching purposes.

Service Layer Approach

In this approach, the service layer assumes responsibility for parsing conditions. This simplifies the data mapper, leaving it with a generic get() method that accepts multiple conditions. However, this may result in domain logic leaking out of the data mapper, as the service layer would handle complex queries.

$bookService->getByAuthorAndPublisher($authorName, $publisherName);

Considerations

The choice between these approaches is subjective, reflecting the developer's preferences. However, a few key factors to consider include:

• Simplicity: The data mapper approach favors a minimalistic interface, reducing complexity.
• Maintainability: The service layer approach may lead to duplicated logic, potentially impacting maintainability.
• Domain Logic Leakage: The service layer approach may compromise the encapsulation of domain logic within the domain object.

Ultimately, the optimal approach depends on the specific context and the priorities of the development team.

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