I will try to answer the question of "why". Imagine a situation where you have a huge database with a lot of columns in a table, and your project/system uses tools to generate entities from database. (Hibernate has those, etc...) Now, suppose that by your business logic you need a particular field NOT to be persisted. You have to "configure" your entity in a particular way. While Transient keyword works on an object - as it behaves within a java language, the @Transient only designed to answer the tasks that pertains only to persistence tasks.

I will try to answer the question of "why". Imagine a situation where you have a huge database with a lot of columns in a table, and your project/system uses tools to generate entities from database. (Hibernate has those, etc...) Now, suppose that by your business logic you need a particular field NOT to be persisted. You have to "configure" your entity in a particular way. While Transient keyword works on an object - as it behaves within a java language, the @Transient only designed to answer the tasks that pertains only to persistence tasks.

通俗地说，如果在实体的属性上使用@Transient注释:该属性将被单独挑选出来，不会保存到数据库中。实体内对象的其余属性仍将被保存。

我保存对象到数据库使用jpa存储库内置的保存方法，这样:

userRoleJoinRepository.save(user2);

对于Kotlin开发人员，请记住Java transient关键字将成为内置的Kotlin @Transient注释。因此，如果您在实体中使用JPA @Transient，请确保您有JPA导入:

import javax.persistence.Transient

Java的transient关键字用于表示字段不被序列化，而JPA的@Transient注释用于表示字段不被持久化到数据库中，也就是说，它们的语义是不同的。

因为它们有不同的含义。@Transient注释告诉JPA提供者不要持久化任何(非瞬态的)属性。另一个告诉序列化框架不要序列化某个属性。您可能希望有一个@Transient属性并仍然序列化它。