实体与DTO之间的区别 [英] Difference between Entity and DTO
问题描述
DTO和实体之间有什么区别？详细地，这些是我的问题：
What is the difference between a DTO and an Entity? In details these are my questions:
-
DTO应该具有哪些字段？例如，我的实体类为：
What fields should the DTOs have? For example my entity classes are:
@Entity
public class MyFirstEntity implements Serializable {
@Id @GeneratedValue
private Long id;
private String stringData;
@OneToOne
private MySecondEntity mySecondEntity;
@OneToMany
private List<MySecondEntity> mySecondEntitesList;
}
@Entity
public class MySecondEntity implements Serializable {
@Id @GeneratedValue
private Long id;
private Integer integerData;
@ManyToOne
private MyFirstEntity myFirstEntity;
}
有一个单面连接（一对一）和一个两面连接（多对一），一个简单的String和Integer数据，当然还有id。在 MyFirstDTO 和 MySecondDTO 类中要从中添加什么？
There is a one-sided connection (One-to-one) and a two-sided connection (Many-to-one), a simple String and Integer data and of course the ids. What to put from them in the MyFirstDTO and MySecondDTO classes?
-
如果实体之间存在继承关系，那么我该如何在DTO中表示它？例如：
If there is an inheritance between the entities, then how should I represent it in the DTOs? For example:
@Entity
public class MyFirstEntity extends MySecondEntity {
....
}
@Entity
public class MyFirstDTO extends MySecondDTO {
....
}
我应该如何使用它们？例如，我发现了这一点：我正在开发一个Web项目。网页的用户想要注册。他/她填写表格，并将其发送到服务器。在服务器端，我首先创建一个DTO，因为其字段具有验证。从DTO中，我创建一个实体并将其持久保存到数据库中。当有实体请求时，我将所请求的实体转换为DTO，并将其提供给客户端的用户。
How should I use them? For example, I find out this: I'm working on a web project. The user of the webpage wants to register. He/She fills the forms, and sends it to the server. On the server side I create first a DTO, because its fields have the validations. From the DTO I create an Entity and persist it to the database. When there is a request for an entity, I convert the requested entity to DTO, and give it to the user on the client side. Is it a good imagination, or not?
推荐答案
简短答案：
-
实体可能是商业域的一部分。因此，它们可以实现行为并将其应用于域内的不同用例。
Entities may be part of a business domain. Thus, they can implement behavior and be applied to different use cases within the domain.
DTO仅用于将数据从一个过程或上下文传输到另一个过程或上下文。因此，它们没有行为-除了非常基本且通常是标准化的存储和检索功能。
DTOs are used only to transfer data from one process or context to another. As such, they are without behavior - except for very basic and usually standardised storage and retrieval functions.
长答案：
虽然术语数据传输对象（DTO）的定义很明确，但是对
术语实体的解释却有所不同在我看来，
While the term "Data Transfer Object" (DTO) is defined quite unambiguously, the term "Entity" is interpreted differently in various contexts.
与实体一词最相关的解释是以下三种：
The most relevant interpretations of the term "Entity", in my opinion, are the following three:
-
在企业级Java和jpa的上下文中：
表示数据库中维护的持久性数据的对象。
In the context of enterprise java and jpa:
"An object that represents persistent data maintained in a database."
在域驱动的设计（由Eric Evans撰写）中：
主要由其身份而不是其属性定义的对象。
In the context of "domain-driven-design" (by Eric Evans):
"An object defined primarily by its identity, rather than its attributes."
在干净的体系结构中（由Robert C. Martin撰写） ：
封装企业范围内关键业务规则的对象。
In the context of "clean architecture" (by Robert C. Martin):
"An object that encapsulates enterprise-wide critical business rules."
< p > Jee和Jpa社区主要将实体视为映射到数据库表
的对象。这种观点与DTO
的定义非常接近-这可能是造成混乱的原因。
The Jee- and Jpa-community sees entities primarily as objects mapped to a database table. This point of view is very close to the definition of a DTO - and that's where much of the confusion probably stems from.
在域-驱动设计以及Robert Martins的观点，
然而，实体是业务领域的一部分，因此
可以并且应该实现行为。
In the context of domain-driven-design, as well as Robert Martins point of view, however, Entities are part of a business domain and thus can and should implement behavior.
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