拥有这些实体：
@Entity
@Data
@Builder
public class User {
@Id
private int id;
private String name;
}
如果我尝试设置id：
@Bean
CommandLineRunner dataLoader(UserRepository userRepo){
return new CommandLineRunner() {
@Override
public void run(String... args) throws Exception {
User u = User.builder()
.id(1)
.name("First User")
.build();
userRepo.save(u);
}
};
}
我得到了
java.lang.IllegalStateException: Failed to execute CommandLineRunner
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:794) ~[spring-boot-2.5.3.jar:2.5.3]
at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:775) ~[spring-boot-2.5.3.jar:2.5.3]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:345) ~[spring-boot-2.5.3.jar:2.5.3]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1343) ~[spring-boot-2.5.3.jar:2.5.3]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1332) ~[spring-boot-2.5.3.jar:2.5.3]
at com.example.demo.DemoApplication.main(DemoApplication.java:16) ~[classes/:na]
Caused by: org.springframework.orm.jpa.JpaSystemException: No default constructor for entity: : com.example.demo.domain.User; nested exception is org.hibernate.InstantiationException: No default constructor for entity: : com.example.demo.domain.User
...
如果我不设置id，那没问题。那么如何手动设置主？
一般来说：您不应该将@Data与实体一起使用，因为如果您有双向实体，生成的equals/hashCode和toString可能会导致StackOverflow Error。
回到你的问题JPA需要一个默认的构造函数（没有args构造函数）
所以我推荐这个：
@Entity
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class User {
@Id
private int id;
private String name;
}
