The identity of an entity should be unique and immutable, meaning it should not change over the course of the entity’s lifespan. Changing an entity’s identity can have serious consequences, such as causing data inconsistencies or breaking relationships with other entities or value objects. For example, if a customer’s ID is changed, it could lead to confusion when tracking their purchase history or other interactions with the system.

It’s important to note that an entity’s attributes, such as name or address, can be mutable without affecting its identity. These changes should be managed through proper encapsulation of the entity’s behavior and business logic.

In summary, the identity of an entity should be unique and immutable, and changes to an entity’s attributes should not affect its identity. By adhering to this principle, developers can create a more consistent and maintainable domain model that accurately represents the business domain.

How to choose a good entity identity

Choosing the right identity for an entity is an important part of designing a domain model in Domain-Driven Design (DDD). Here are some good practices for choosing the identity of an entity:

1. Choose a unique identity: An entity’s identity should be unique within the domain model, and it should not change during the entity’s lifespan. An entity’s identity should be determined by the business requirements, such as a unique identifier like a serial number, a customer ID, or a social security number.
2. Choose a stable identity: An entity’s identity should be stable, meaning it should not change over time. A stable identity allows for consistency and accuracy in the domain model, and it can prevent errors in the system. For example, if a customer’s ID changes, it can be confusing to track their purchase history or other interactions with the system.
3. Choose an identity that is easily identifiable: An entity’s identity should be easily identifiable, preferably by a human reader. For example, using a UUID or GUID may not be as easily recognizable as a customer’s name or ID number.
4. Choose an identity that can be used consistently throughout the domain model: An entity’s identity should be consistent throughout the domain model, and it should be used consistently in all contexts where the entity is referenced.
5. Consider scalability and performance: Choosing an identity that can scale well and perform well is also important, especially for systems with high volumes of data or high throughput.

By following these practices, developers can choose an appropriate identity for entities that accurately represents the domain model and provides a flexible and maintainable software solution.