In Domain-Driven Design (DDD), services are categorized into three main types: Domain Services, Application Services, and Infrastructure Services. Each type of service has a distinct role and purpose within the architecture of a software system. Here is a detailed explanation of the differences between them:
Domain Services
Domain Services encapsulate business logic that does not naturally fit within a single domain entity or value object. They are part of the domain layer and are responsible for implementing core business rules and operations that span multiple entities. Domain Services are stateless and focus solely on the business logic without any dependencies on external systems or infrastructure.
Key Characteristics:
Encapsulate Business Logic: They handle business operations that involve multiple entities or complex business rules.
Stateless: They do not maintain any state between method calls.
Independent of Infrastructure: They do not interact directly with external systems or infrastructure components.
Reusable: They can be reused across different parts of the application where the same business logic is needed.
Example:
A service that calculates the total price of an order, including discounts and taxes, based on the items in the order and the customer's status.
Application Services
Application Services are part of the application layer and are responsible for orchestrating the use cases of the application. They act as a bridge between the presentation layer (e.g., user interfaces, APIs) and the domain layer. Application Services coordinate the flow of data between the user interface and the domain model, invoking domain services and repositories as needed.
Key Characteristics:
Orchestrate Use Cases: They implement the application's use cases by coordinating domain services, repositories, and other application services.
Handle Data Transfer: They often work with Data Transfer Objects (DTOs) to transfer data between the presentation layer and the domain layer.
Interact with External Systems: They may call external services or APIs to fulfill a use case.
Stateless: Like domain services, they are typically stateless.
Example:
A service that handles the process of placing an order, which involves validating the order, calculating the total price using a domain service, and saving the order to the database.
Infrastructure Services
Infrastructure Services are part of the infrastructure layer and are responsible for handling technical concerns and external system interactions. They provide implementations for interfaces defined in the domain layer, such as repositories, messaging systems, and external APIs. Infrastructure Services abstract away the details of interacting with external syste...
