What is an Entity in Clean Architecture?

In Clean Architecture, an entity is a core component that encapsulates the business logic and represents the fundamental concepts of the problem domain. Entities are designed to be independent of any specific implementation details, frameworks, or external systems, ensuring that they remain pure and focused on the business rules and logic they encapsulate.

Key Characteristics of Entities in Clean Architecture:

1. Encapsulation of Business Logic:

   • Entities hold the core business logic and rules of the system. They are responsible for maintaining the integrity and consistency of the business data and operations[1].

2. Independence from Use Cases and Infrastructure:

   • Entities are not tied to any specific use cases or infrastructure components. This separation ensures that changes in the application logic or infrastructure do not directly impact the entities[1].

3. Identity and State:

   • Entities are defined by their unique identity rather than their attributes. This means that an entity is recognized by its identity, which remains consistent throughout its lifecycle, even if its attributes change[5].

4. Pure Data Structures:

   • Entities are typically implemented as pure data structures with methods that operate on their data. This design helps in keeping the business logic centralized within the entity itself[1].

Example of an Entity:

Here is an example of a Product entity in TypeScript:

class Product {
  constructor(
    public id: number,
    public name: string,
    public description: string,
    public price: number,
    public available: boolean
  ) {}

  canBePurchased(): boolean {
    return this.available && this.price > 0;
  }
}

In this example, the Product entity encapsulates the business logic related to whether a product can be purchased based on its availability and price[1].

Mapping Between Entities and Models:

In Clean Architecture, entities are often mapped to models that represent the state of the system at a particular point in time. This mapping is necessary to transform data between the format used by the entities and the format required by external systems or us...