DDD：实体可以具有原始数据类型的属性吗？

Question

The domain driven design differentiates two model types: entities and value objects. In the most examples the attributes of an entity are value objects or other entities, while the attributes of a value object are mostly simple strings, integers etc. (ie primitive data types).

That leads me to the question: Can an entity also have attributes of primitive data types? Or do you normally model each attribute of an entity as a value object or another entity?

The following might be an example to answer this question: We have an entity Comment with an attribute text . Is text simply a string variable or a value object?

Answer 1

While it is common attitude to compose an entity of another entities or value objects, it is not necessary. Please remember that you should think about an abstraction. Primitive types are ok when there is no business logic involved in using them. For example:

public class User {
    private UserId id;
    private String nickname;
    private Date joinDate;
}

As you can see, nickname is an primitive type, because we can't do anything special with nickname. On the other hand joinDate should be Value Object, because dates has some logic (as comparing dates, adding, subtracting etc.)

Even in "Implemeting Domain-Driven Design" by Vaughn Vernon are examples of entities composed of primitive types.