大佬教程收集整理的这篇文章主要介绍了如何在Spring Data JPA中解决LazyInitializationException?,大佬教程大佬觉得挺不错的,现在分享给大家,也给大家做个参考。
基本上,你需要在事务内部时获取惰性数据。如果你的服务类别为@transactional
,那么你在其中时一切都应该没问题。退出服务类后,如果尝试get延迟集合,你将获得该异常,该异常位于@H_190_3@main()方法line中System.out.println(random.getCreatedJobs())
;。
现在,归结为你需要返回的服务方法。如果userservice.getRandomUser()
期望返回一个初始化了作业的用户,以便你可以对其进行操作,则该方法的责任是取回它。使用Hibernate最简单的方法是调用Hibernate.initialize(user.getCreatedJobs()
)。
我必须参加具有一对多关系的课程。当我尝试访问延迟加载的集合时,出现·。我在网上搜索了一段时间,现在我知道我得到了异常,因为用于加载保存集合的类的会话已关闭。但是我没有找到解决方案(或者至少我不理解它们)。基本上我有那些课:
User
@Entity
@Table(name = "user")
public class User {
@Id
@GeneratedValue
@column(name = "id")
private long id;
@OneToMany(mappedBy = "creator")
private Set<Job> createdJobs = new HashSet<>();
public long getId() {
return id;
}
public void setId(final long id) {
this.id = id;
}
public Set<Job> getCreatedJobs() {
return createdJobs;
}
public void setCreatedJobs(final Set<Job> createdJobs) {
this.createdJobs = createdJobs;
}
}
UserRepository
public interface UserRepository extends JpaRepository<User,Long> {}
Userservice
@service
@transactional
public class Userservice {
@Autowired
private UserRepository repository;
Boolean usersAvailable = false;
public void addSomeUsers() {
for (int i = 1; i < 101; i++) {
final User user = new User();
repository.save(user);
}
usersAvailable = true;
}
public User getRandomUser() {
final Random rand = new Random();
if (!usersAvailablE) {
addSomeUsers();
}
return repository.findOne(rand.nexTint(100) + 1L);
}
public List<User> getAllUsers() {
return repository.findAll();
}
}
Job
@Entity
@Table(name = "job")
@Inheritance
@Discriminatorcolumn(name = "job_type",discriminatorType = DiscriminatorType.StriNG)
public abstract class Job {
@Id
@GeneratedValue
@column(name = "id")
private long id;
@manyToOne
@Joincolumn(name = "user_id",nullable = falsE)
private User creator;
public long getId() {
return id;
}
public void setId(final long id) {
this.id = id;
}
public User getCreator() {
return creator;
}
public void setCreator(final User creator) {
this.creator = creator;
}
}
JobRepository
public interface JobRepository extends JpaRepository<Job,Long> {}
Jobservice
@service
@transactional
public class Jobservice {
@Autowired
private JobRepository repository;
public void addJob(final Job job) {
repository.save(job);
}
public List<Job> getJobs() {
return repository.findAll();
}
public void addJobsForUsers(final List<User> users) {
final Random rand = new Random();
for (final User user : users) {
for (int i = 0; i < 20; i++) {
switch (rand.nexTint(2)) {
case 0:
addJob(new HelloWorldJob(user));
break;
default:
addJob(new GoodbyeWorldJob(user));
break;
}
}
}
}
}
App
@Configuration
@EnableAutoConfiguration
@ComponentScan
public class App {
public static void main(final String[] args) {
final ConfigurableApplicationContext context = SpringApplication.run(App.class);
final Userservice userservice = context.getBean(Userservice.class);
final Jobservice jobservice = context.getBean(Jobservice.class);
userservice.addSomeUsers(); // Generates some users and stores them in the db
jobservice.addJobsForUsers(userservice.getAllUsers()); // Generates some jobs for the users
final User random = userservice.getRandomUser(); // Picks a random user
System.out.println(random.getCreatedJobs());
}
}
我经常读到会话必须绑定到当前线程,但是我不知道如何使用Spring的基于注释的配置来做到这一点。有人可以指出我该怎么做吗?
PS我想使用延迟加载,因此急于加载是没有选择的。
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