What is the difference between Domain Objects, POCO, Services, Repositories and Entities?

To answer the interview question "What is the difference between Domain Objects, POCO, Services, Repositories, and Entities?" in the context of Domain-Driven Design (DDD), it's important to understand the distinct roles and characteristics of each concept. Here is a detailed explanation:

Domain Objects

Domain Objects are central to Domain-Driven Design. They encapsulate the business logic and rules of the domain. These objects represent concepts from the business domain and are responsible for maintaining the integrity of the business rules.

• Characteristics:
  • Encapsulate business logic.
  • Represent real-world concepts.
  • Ensure the integrity of business rules.
  • Can include entities, value objects, and aggregates.

POCO (Plain Old CLR Object)

POCOs are simple objects that do not depend on any framework-specific base class. They are used to represent data without any persistence logic or business logic.

• Characteristics:
  • Simple data containers.
  • No dependency on any framework.
  • No persistence logic (Persistence Ignorance).
  • Often used in conjunction with ORMs like Entity Framework.

Services

Services in DDD are used to encapsulate domain logic that does not naturally fit within a domain object or entity. There are two main types of services:

• Domain Services:

  • Contain domain logic that spans multiple entities or value objects.
  • Stateless and operate on domain objects.
  • Example: A service that calculates discounts based on various business rules.

• Application Services:

  • Orchestrate the use of domain objects and domain services.
  • Handle tasks like transaction management, authorization, and coordination of domain operations.
  • Example: A service that handles user registration by coordinating various domain services and entities.

Repositories

Repositories are used to abstract the data access layer. They provide a collection-like interface for accessing domain objects and ensure that the domain model remains decoupled from the data access logic.

• Characteristics:
  • Abstract data access logic.
  • Provide methods for CRUD operations.
  • Ensure t...