How should a model be structured in MVC?

In MVC, the model represents the business logic and data of the application. It encapsulates domain-specific logic and rules, enabling the application to perform tasks and make decisions without relying on the UI or controller.

Concept of Model:

• A model is not a class or object. It's a layer composed of three main elements:

  • Domain Objects: Represent business entities and contain logic specific to the problem domain.
  • Data Mappers: Handle data persistence and interaction with external storage, such as databases.
  • Services: Orchestrate interactions between domain objects and data mappers, providing a higher-level interface for interacting with the business logic.

Separation of Concerns:

• The model layer is separate from the UI layer (view and controller).
• Communication with the model occurs solely through services, ensuring a clear separation of concerns and preventing domain logic leakage into UI or controller code.
• This separation promotes the Single Responsibility Principle (SRP), flexibility, and easier testability.

Accessing the Model:

• In views and controllers, you can access model services through dependency injection using frameworks like Symfony's DI container or Auryn.
• Services can be injected into constructors or accessed through a factory.
• This approach ensures that all necessary services are available to these components.

Modifying Model State:

• Controllers are responsible for handling user input and modifying the model state.
• They call service methods, which in turn interact with domain objects and data mappers to perform necessary logical operations.

Data Persistence:

• Domain Objects represent business entities but are not aware of storage.
• Data Mappers handle data persistence and retrieval from external storage.
• This separation allows business logic to remain independent of the specific storage technology used.

Benefits of Separation:

• Enforces SRP by assigning clear responsibilities to each layer.
• Improves code readability and testability by isolating business logic.
• Provides flexibility in modifying business logic or data storage without impacting other components.
• Simplifies development of external APIs by providing a consistent interface for accessing model services.

Additional Comments:

• Database tables do not always map directly to domain objects and data mappers.
• Views are not templates but handle presentational logic and template selection.
• There should be a 1:1 relationship between views and controllers for each page or screen.