In Clean Architecture, data flow is a critical concept that ensures the separation of concerns and maintains the integrity of the system's structure. The data flow in Clean Architecture can be understood through its layered approach, where each layer has distinct responsibilities and dependencies are directed inward, towards the core business logic. Here’s a detailed explanation of the data flow in Clean Architecture:
Layers in Clean Architecture
Entities (Domain Layer):
This innermost layer contains the core business logic and entities. These entities are the fundamental business objects of the application and are independent of any external systems or frameworks.
Data Flow: Entities receive data from the Use Cases layer and provide business logic operations.
Use Cases (Application Layer):
This layer contains the application-specific business rules. It orchestrates the flow of data to and from the entities and ensures that the business rules are applied correctly.
Data Flow: Use Cases interact with the Entities to perform business operations and then pass the results to the Interface Adapters layer.
Interface Adapters (Adapters Layer):
This layer is responsible for converting data from the format most convenient for the use cases and entities to the format required by the external systems (e.g., databases, web services, user interfaces).
Data Flow: Interface Adapters receive data from the Use Cases, adapt it as necessary, and then pass it to the Frameworks and Drivers layer. Conversely, they also receive data from external systems, adapt it, and pass it to the Use Cases.
Frameworks and Drivers (Infrastructure Layer):
This outermost layer contains the implementation details such as databases, web frameworks, and other external systems.
Data Flow: This layer interacts with the Interface Adapters to send and receive data from external systems. It does not contain any business logic.
Dependency Rule
A key principle in Clean Architecture is the Dependency Rule, which states that source code dependencies can only point inward. This means that:
The Frameworks and Drivers layer depends on the Interface Adapters layer.
The Interface Adapters layer depends on the Use Cases layer.
The Use Cases layer depends on the Entities layer.
No inner layer should know anything about the outer layers.
Example of Data Flow
Consider a scenario where a user requests data through a web interface:
User Interface (Frameworks and Drivers): The user initiates a request through the UI.
Controller (Interface Adapters): The request is handled by a controller, which converts the request into a format suitable for the Use Cases.
Use Case (Application Layer): The controller calls a use case, passing the necessary data. The us...
