Java LazyInitializationException，即使使用@Transactional
当我去获取一个用户的评论时，很难让一个简单的由多个实体映射的OneToMany工作。其他答案建议您必须使用entityManager自己创建查询，但这似乎太可怕了。如果你甚至不能在没有硬编码内联sql的情况下做这样简单的事情，那么ORM有什么意义呢？似乎更可能是我做错了什么 似乎这可能与我正在使用该模型从jsp访问user.getComments（）方法有关。不知道最好的方法是什么 模式：Java LazyInitializationException，即使使用@Transactional,java,sql,spring,kotlin,jpql,Java,Sql,Spring,Kotlin,Jpql,当我去获取一个用户的评论时，很难让一个简单的由多个实体映射的OneToMany工作。其他答案建议您必须使用entityManager自己创建查询，但这似乎太可怕了。如果你甚至不能在没有硬编码内联sql的情况下做这样简单的事情，那么ORM有什么意义呢？似乎更可能是我做错了什么 似乎这可能与我正在使用该模型从jsp访问user.getComments（）方法有关。不知道最好的方法是什么 模式： CREATE TABLE users ( id INTEGER AUTO_INCREMENT PR
CREATE TABLE users (
id INTEGER AUTO_INCREMENT PRIMARY KEY,
username VARCHAR(255) UNIQUE NOT NULL,
created_at TIMESTAMP DEFAULT NOW()
);
CREATE TABLE comments (
id INTEGER AUTO_INCREMENT PRIMARY KEY,
comment_text VARCHAR(255) NOT NULL,
photo_id INTEGER NOT NULL,
user_id INTEGER NOT NULL,
created_at TIMESTAMP DEFAULT NOW(),
FOREIGN KEY(user_id) REFERENCES users(id)
);
@RequestMapping("/user")
public ModelAndView getUser(@RequestParam int id) {
return new ModelAndView("user", "message", userService.getUser(id));
}
@Service
public class UserService {
private UserDAO userDAO;
@Autowired
public UserService(UserDAO userDAO) {
this.userDAO = userDAO;
}
@Transactional
public User getUser(int id) {
return userDAO.getUser(id);
}
}
@Repository
public class UserDAO {
@PersistenceContext
EntityManager entityManager;
@Nullable
public User getUser(int id)
{
return entityManager.find(User.class, id);
}
}
@Entity
@Table(name="users")
public class User {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(name="id")
private int id;
@Column(name="username")
private String userName;
@Temporal(TemporalType.TIMESTAMP)
@Column(name="created_at")
private Date createdAt;
@OneToMany(mappedBy="user")
private List<Comment> comments;
public int getId() {
return id;
}
public String getUserName() {
return userName;
}
public Date getCreatedAt() {
return createdAt;
}
@Transactional
public List<Comment> getComments() {
return comments;
}
}
@Entity
@Table(name="comments")
public class Comment {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(name="id")
private int id;
@Column(name="comment_text")
private String commentText;
@Column(name="photo_id")
private int photoId;
@ManyToOne
@JoinColumn(name="user_id")
private User user;
@Temporal(TemporalType.TIMESTAMP)
@Column(name = "created_at")
private Date createdAt;
@Override
public String toString() {
return "Comment [id=" + id + ", commentText=" + commentText + ", photoId=" + photoId + ", userId=" + user.getId()
+ ", createdAt=" + createdAt + "]";
}
public int getId() {
return id;
}
public String getCommentText() {
return commentText;
}
public int getPhotoId() {
return photoId;
}
public User getUser() {
return user;
}
public Date getCreatedAt() {
return createdAt;
}
}
@Transactional
public User getUser(int id) {
User user = userDAO.getUser(id);
user.getComments().size(); //initializing
return user;
}
public List<User> getAllUsers()
{
TypedQuery<User> query = entityManager.createQuery("SELECT e from User e left join fetch e.comments", User.class);
return (List<User>) query.getResultList();
}
@Nullable
public User getUser(int id)
{
TypedQuery<User> query = entityManager.createQuery("SELECT e from User e left join fetch e.comments c where e.id = :id", User.class);
query.setParameter("id", id);
return query.getSingleResult();
}
@Configuration
@EnableTransactionManagement
public class AppConfig {
@Bean
public LocalContainerEntityManagerFactoryBean factoryBean() {
LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean();
factory.setPersistenceProviderClass(HibernatePersistenceProvider.class);
return factory;
}
@Bean
public PlatformTransactionManager transactionManager(){
JpaTransactionManager transactionManager = new JpaTransactionManager();
transactionManager.setEntityManagerFactory(factoryBean().getObject() );
return transactionManager;
}
}
@Transactional
public User getUser(int id) {
User user = userDAO.getUser(id);
Hibernate.initialize(user.getComments());
return user;
}