交易注释没有解决 org.hibernate.LazyInitializationException
Transactional annotation doesn't solve org.hibernate.LazyInitializationException
我正在编写一个简单的 Spring Data JPA 应用程序。我使用 MySQL 数据库。有两个简单的表格:
- 部门
- 员工
每个员工在某个部门工作 (Employee.department_id)。
我有两个实体 classes:
@Entity
public class Department {
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Id
private Long id;
@Basic(fetch = FetchType.LAZY)
@OneToMany(mappedBy = "department")
List<Employee> employees;
}
@Entity
public class Person {
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Id
private Long id;
@ManyToOne
@JoinColumn
private Department department;
}
存储库:
@Repository
public interface DepartmentRepository extends JpaRepository<Department, Long> {}
@Repository
public interface EmployeeRepository extends JpaRepository<Employee, Long> {}
有一个 DepartmentService class:
@Service
@Transactional
public class DepartmentService {
@Autowired
DepartmentRepository departmentRepository;
@Transactional
List<Department> getAll() {
departmentRepository.findAll();
}
@Transactional
void getEmployees() {
for(Department department: getAll()) {
List<Employee> employees = department.getEmployees();
for(Employee employee: employees)
System.out.println(employee);
}
}
}
和主要的class(我不需要网络,所以我使用CommandLineRunner
到运行作为控制台应用程序的应用程序):
@SpringBootApplication
public class EmployeeDB implements CommandLineRunner {
@Autowired
DepartmentService departmentService;
public static void main(String[] args) {
SpringApplication.run(EmployeeDB.class, args);
}
@Override
public void run(String... args) throws Exception {
departmentService.getEmployees();
}
}
我在 class DepartmentService
之前以及它的所有方法之前添加了 @Transactional
,但我仍然不断收到以下错误:
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: employeeDB.Department.employees, could not initialize proxy - no Session
堆栈跟踪:
Caused by: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: employeeDB.Department.employees, could not initialize proxy - no Session
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:602) ~[hibernate-core-5.4.2.Final.jar:5.4.2.Final]
at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:217) ~[hibernate-core-5.4.2.Final.jar:5.4.2.Final]
at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:581) ~[hibernate-core-5.4.2.Final.jar:5.4.2.Final]
at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:148) ~[hibernate-core-5.4.2.Final.jar:5.4.2.Final]
at org.hibernate.collection.internal.PersistentBag.iterator(PersistentBag.java:303) ~[hibernate-core-5.4.2.Final.jar:5.4.2.Final]
at employeeDB.DepartmentService.getEmployees(DepartmentService.java:25) ~[main/:na]
at employeeDB.EmployeeDB.run(EmployeeDB.java:41) [main/:na]
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:795) [spring-boot-2.3.3.RELEASE.jar:2.3.3.RELEASE]
... 5 common frames omitted
为什么会出现此错误?我该如何解决?
@Transactional
不应该用于获取延迟加载的实体,这将导致 n+1 select problem.
您需要使用适当的映射或查询,例如在 jpql 中:
select d
from Department d
left join fetch d.employees
总结以上所有答案和评论:
发生这种情况是因为方法 DepartmentService::getEmployees
不是 public。
I added public before getEmployees() and this sloved the problem.
@Transactional
注解由 AOP 提供支持,那么代理只能处理 public 个方法。
这意味着@Transactional
实际上并没有应用到这个方法,并且会话已经在读取惰性集合的时刻关闭了。
我正在编写一个简单的 Spring Data JPA 应用程序。我使用 MySQL 数据库。有两个简单的表格:
- 部门
- 员工
每个员工在某个部门工作 (Employee.department_id)。
我有两个实体 classes:
@Entity
public class Department {
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Id
private Long id;
@Basic(fetch = FetchType.LAZY)
@OneToMany(mappedBy = "department")
List<Employee> employees;
}
@Entity
public class Person {
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Id
private Long id;
@ManyToOne
@JoinColumn
private Department department;
}
存储库:
@Repository
public interface DepartmentRepository extends JpaRepository<Department, Long> {}
@Repository
public interface EmployeeRepository extends JpaRepository<Employee, Long> {}
有一个 DepartmentService class:
@Service
@Transactional
public class DepartmentService {
@Autowired
DepartmentRepository departmentRepository;
@Transactional
List<Department> getAll() {
departmentRepository.findAll();
}
@Transactional
void getEmployees() {
for(Department department: getAll()) {
List<Employee> employees = department.getEmployees();
for(Employee employee: employees)
System.out.println(employee);
}
}
}
和主要的class(我不需要网络,所以我使用CommandLineRunner
到运行作为控制台应用程序的应用程序):
@SpringBootApplication
public class EmployeeDB implements CommandLineRunner {
@Autowired
DepartmentService departmentService;
public static void main(String[] args) {
SpringApplication.run(EmployeeDB.class, args);
}
@Override
public void run(String... args) throws Exception {
departmentService.getEmployees();
}
}
我在 class DepartmentService
之前以及它的所有方法之前添加了 @Transactional
,但我仍然不断收到以下错误:
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: employeeDB.Department.employees, could not initialize proxy - no Session
堆栈跟踪:
Caused by: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: employeeDB.Department.employees, could not initialize proxy - no Session
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:602) ~[hibernate-core-5.4.2.Final.jar:5.4.2.Final]
at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:217) ~[hibernate-core-5.4.2.Final.jar:5.4.2.Final]
at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:581) ~[hibernate-core-5.4.2.Final.jar:5.4.2.Final]
at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:148) ~[hibernate-core-5.4.2.Final.jar:5.4.2.Final]
at org.hibernate.collection.internal.PersistentBag.iterator(PersistentBag.java:303) ~[hibernate-core-5.4.2.Final.jar:5.4.2.Final]
at employeeDB.DepartmentService.getEmployees(DepartmentService.java:25) ~[main/:na]
at employeeDB.EmployeeDB.run(EmployeeDB.java:41) [main/:na]
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:795) [spring-boot-2.3.3.RELEASE.jar:2.3.3.RELEASE]
... 5 common frames omitted
为什么会出现此错误?我该如何解决?
@Transactional
不应该用于获取延迟加载的实体,这将导致 n+1 select problem.
您需要使用适当的映射或查询,例如在 jpql 中:
select d
from Department d
left join fetch d.employees
总结以上所有答案和评论:
发生这种情况是因为方法 DepartmentService::getEmployees
不是 public。
I added public before getEmployees() and this sloved the problem.
@Transactional
注解由 AOP 提供支持,那么代理只能处理 public 个方法。
这意味着@Transactional
实际上并没有应用到这个方法,并且会话已经在读取惰性集合的时刻关闭了。