What is the difference between VO and DTO?

VO (Value Object) and DTO (Data Transfer Object) are two common design patterns used to transfer data between different layers of an application.

Value Object (VO) is an object used to encapsulate a set of related data, typically immutable. VOs are commonly used to represent values in a domain model, such as the attributes of an entity. They are mainly used to encapsulate the structure of data without containing business logic. VOs make it easy to pass data between different layers, like transferring data between controllers and views. The properties of a VO are typically read-only, as their values should not be altered.

DTO, or Data Transfer Object, is an object used to transfer data between different layers of an application. It is typically used to encapsulate data from a database or external service, as well as to transfer data to other layers. The properties in a DTO can be read and written, as their values may need to be updated and passed between different layers. The purpose of a DTO is to pass data from one layer to another in order to decouple the details of data transfer between different layers.

Therefore, VOs are mainly used to encapsulate values in domain models, while DTOs are mainly used to transfer data between different layers. VOs are immutable, while DTOs can be mutable. VOs typically encompass the data structure of domain models, while DTOs can contain any data from databases or external services.