Spring Hibernate：尽管被配置，@Transactional在Spring Data JPA中不起作用 [英] Spring Hibernate: @Transactional is not working in Spring Data JPA despite being configured

问题描述

LazyInitializationException：未能懒惰地初始化一个关系收集角色，无法初始化代理 - 无会话

我知道使用Eager获取类型可以正常工作，但这将是一个头痛和性能滞后于应用程序，所以，我必须继续考虑Lazy fetch类型。

我读到使用Spring Data JPA时， @Transactional 会初始化惰性关系，但它似乎对我没有影响。

这是我的应用程序的外观：

实体

课程实体
$ b

  @Entity 
 @Table（name =course）
 @Transactional  
 public class Course {
 
 
 @Id 
 @GeneratedValue（strategy = GenerationType.AUTO）
 private Intege r id; 
 
 @Column（name =course_name）
 private String courseName; 
 
 @Column（name =course_description）
 private String courseDescription; 
 
 @ManyToMany（cascade = {CascadeType.MERGE，CascadeType.DETACH，CascadeType.REFRESH，CascadeType.PERSIST}）
 @JoinTable（
 name =course_student，
 joinColumns = @JoinColumn（name =course_id），
 inverseJoinColumns = @JoinColumn（name =student_id））
 private List< Student>学生们; 
  

学生实体

  @Entity 
 @Table（name =students）
 public class Student {
 
 @I $ 
 @GeneratedValue（strategy = GenerationType.AUTO）
私人整数ID; 
 
私人字符串名称; 
 
私人字符串等级; 
 
 @ManyToMany（cascade = {CascadeType.MERGE，CascadeType.DETACH，CascadeType.REFRESH，CascadeType.PERSIST}，fetch = FetchType.EAGER）
 @JoinTable（
 name = course_student，
 joinColumns = @JoinColumn（name =student_id），
 inverseJoinColumns = @JoinColumn（name =course_id））
 List< Course>培训班; 
  

控制器

  @Controller 
 @RequestMapping（/ courses）
 @Transactional 
 public class CourseController {
 
 ... 。
 
 @GetMapping（get-joined-students）
 ModelAndView getJoined（）{
 
课程course = courseRepo.findById（6）.get（） ; （学生学生：
 course.getStudents（））{
 
 System.out.println（Student：+ student）; 
 
 
} 
 
 
 ModelAndView modelAndView = new ModelAndView（redirect：list）; 
 
返回modelAndView; 
} 
  

}

存储库

课程库

  @Repository 
 public interface CourseRepo扩展JpaRepository< Course，Integer> {} 
  

学生资源库

  @Repository 
 public interface StudentRepo扩展JpaRepository< Student，Integer> {} 
  

Servlet配置文件

 <？xml version =1.0encoding =UTF-8？> 
< beans xmlns =http://www.springframework.org/schema/beans....> 
 
< context：annotation-config /> 
 
< context：component-scan base-package =com.company.springdemo/> 
 
< mvc：annotation-driven /> 
 
 ... 
 
  
< bean id =transactionManagerJPAclass =org.springframework.orm.jpa.JpaTransactionManager> 
< property name =dataSourceref =myDataSource/> 
< / bean> 
 
< tx：annotation-driven transaction-manager =transactionManagerJPA/> 
 
 
< bean id =EMF
 class =org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean> 
< property name =packagesToScanvalue =com.company.springdemo.entity/> 
< property name =dataSourceref =myDataSource/> 
 
< property name =jpaProperties> 
<道具> 
< prop key =hibernate.show_sql> true< / prop> 
< prop key =hibernate.hbm2ddl.auto> update< / prop> 
< prop key =hibernate.dialect> org.hibernate.dialect.MySQL57Dialect< / prop> 
< prop key =hibernate.show_sql> false< / prop> 
< prop key =hibernate.format_sql> true< / prop> 
< /道具> 
< / property> 
 
< property name =persistenceProvider> 
< bean class =org.hibernate.jpa.HibernatePersistenceProvider/> 
< / property> 
< / bean> 
  

我可能会做什么错误？

解决方案

我认为你在这里混淆了一些东西。

您有多个选择：
$ b

1. 访问交易中的关系


2. 使用EAGER提取


3. 对 FETCH JOIN使用自定义查询


4. 使用投影

另请阅读我的文章以了解更多详情： https://blog.arnoldgalovics.com/2017/02/27/lazyinitializationexception-demystified/
https://blog.arnoldgalovics.com/2017/03/14/using-projections-in-your-data-access-层/

I have been receiving this error all the time when using Lazy evaluation in a ManyToMany relationship:

LazyInitializationException: failed to lazily initialize a collection of roles, could not initialize proxy - no Session

I know that using Eager fetch type will work fine, but this will be a headache and a performance lag to the application, so, I have to continue considering the Lazy fetch type.

I read that when using Spring Data JPA, @Transactional will initialize the lazy relations, but it doesn't seem to take effect with me.

Here is how my app look like:

Entities

Course Entity

@Entity
@Table(name = "course")
@Transactional
public class Course {


@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;

@Column(name = "course_name")
private String courseName;

@Column(name = "course_description")
private String courseDescription;

@ManyToMany(cascade = {CascadeType.MERGE,CascadeType.DETACH,CascadeType.REFRESH,CascadeType.PERSIST})
@JoinTable(
        name = "course_student",
        joinColumns = @JoinColumn(name = "course_id"),
        inverseJoinColumns = @JoinColumn(name = "student_id") )
private List<Student> students;

Student Entity

@Entity
@Table(name = "students")
public class Student {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;

private String name;

private String grade;

@ManyToMany(cascade = {CascadeType.MERGE,CascadeType.DETACH,CascadeType.REFRESH,CascadeType.PERSIST},fetch = FetchType.EAGER)
@JoinTable(
        name = "course_student",
        joinColumns = @JoinColumn(name = "student_id"),
        inverseJoinColumns = @JoinColumn(name = "course_id") )
List<Course> courses;

Controller

@Controller
@RequestMapping("/courses")
@Transactional
public class CourseController {

....

@GetMapping("get-joined-students")
ModelAndView getJoined() {

    Course course = courseRepo.findById(6).get();

    for (Student student :
            course.getStudents()) {

        System.out.println("Student: " + student);
    }


    ModelAndView modelAndView = new ModelAndView("redirect:list");

    return modelAndView;
}

}

Repositories

Course Repository

@Repository
public interface CourseRepo extends JpaRepository<Course,Integer> {}

Student Repository

@Repository
public interface StudentRepo extends JpaRepository<Student,Integer> { }

Servlet Configuration File

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"  ....    >

<context:annotation-config/>

<context:component-scan base-package="com.company.springdemo"/>

<mvc:annotation-driven/>

....

<jpa:repositories transaction-manager-ref="transactionManagerJPA" base-package="com.company.springdemo" entity-manager-factory-ref="EMF" />

<bean id="transactionManagerJPA" class="org.springframework.orm.jpa.JpaTransactionManager" >
    <property name="dataSource" ref="myDataSource" />
</bean>

<tx:annotation-driven transaction-manager="transactionManagerJPA" />


<bean id="EMF"
      class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="packagesToScan" value="com.company.springdemo.entity" />
    <property name="dataSource" ref="myDataSource" />

    <property name="jpaProperties">
        <props>
            <prop key="hibernate.show_sql">true</prop>
            <prop key="hibernate.hbm2ddl.auto">update</prop>
            <prop key="hibernate.dialect">org.hibernate.dialect.MySQL57Dialect</prop>
            <prop key="hibernate.show_sql">false</prop>
            <prop key="hibernate.format_sql">true</prop>
        </props>
    </property>

    <property name="persistenceProvider">
        <bean class="org.hibernate.jpa.HibernatePersistenceProvider" />
    </property>
</bean>

What potentially could I be doing wrong?

解决方案

I think you are mixing up things here. LazyInitializationException is popping up as you are trying to fetch the relation when the transaction is already over.

You have multiple choices:

1. Access the relation within the transaction
2. Use EAGER fetching
3. Use custom queries with FETCH JOIN
4. Use Projections

Also read my article for more details: https://blog.arnoldgalovics.com/2017/02/27/lazyinitializationexception-demystified/ https://blog.arnoldgalovics.com/2017/03/14/using-projections-in-your-data-access-layer/

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