DTO, VO, Entity

What Is a DTO(Data Transfer Object)?

DTO means an object used to transfer or move data.
It is an object(Java Beans) for exchanging data between layers.
- It refers to an object used when data retrieved from a DB is sent to a Service, Controller, and so on.
- It is a pure data object without logic and has only Getter and Setter methods.

VO(Value Object) literally means a value object.
It guarantees object immutability, meaning the object’s information does not change.
- It may only have Getter methods.
- Values can be set through a constructor, and using the Builder pattern is convenient in this case.
Even if VO instances have different names, if all their property values are the same, the two instances can be considered the same object.
- For this, a VO must override the equals() and hashcode() methods of the Object class.
A VO is judged to be the same object only when all values of the properties(fields) declared inside the VO are equal for each VO object.
It can have additional properties beyond the columns in a table.
A BaseVO class that collects common properties for multiple tables(A, B, C) can also be inherited and used.

An Entity is an object mapped to an actual DB table.
It means a collection of data.
It is data that must be stored and managed.
It refers to concepts, places, events, and similar things.
It refers to tangible or intangible subjects.
Each Entity must be distinguished by an ID and must have a unique identifier.
- ID, member number, and so on.
It must have at least one property.
- Name, address, and so on.
It is a set of instances that exist persistently.
It must be information that is necessary and managed in the relevant business domain.

Layer separation