在JPA / hiberante中的多对多映射中添加（fetch = FetchType.EAGER）后出现问题

时间：2019-08-01 15:26:20

标签： java spring hibernate spring-boot jpa

我有Course.java类：

package com.ashwin.jpa.hiberante.jpaapp.entity;

import org.hibernate.annotations.CreationTimestamp;
import org.hibernate.annotations.UpdateTimestamp;

import javax.persistence.*;
import java.time.LocalDateTime;
import java.util.ArrayList;
import java.util.List;

@Entity
@Table(name="course")

public class Course {

    @Id
    @GeneratedValue
    private Long id;

    @Column(name="name",nullable = false)
    private String name;

    @UpdateTimestamp
    private LocalDateTime localDateTime;

    @CreationTimestamp
    private LocalDateTime createdDate;


    //one to many
    @OneToMany(mappedBy = "course",fetch = FetchType.EAGER)
    private List<Review> reviewList=new ArrayList<>();



    //many to many
    @ManyToMany(mappedBy = "courses")
    private List<Student> students=new ArrayList<>();

    public Course(String name) {
        this.name = name;
    }

    public Course(){

        this.name=name;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Course{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }

    public List<Review> getReviewList() {
        return reviewList;
    }

    public void setReview(Review review) {
        this.reviewList.add(review);
    }

    public void removeReview(Review review) {
        this.reviewList.remove(review);
    }

    public List<Student> getStudents() {
        return students;
    }

    public void setStudent(Student student) {
        this.students.add(student);
    }
}

我有Student.java类

package com.ashwin.jpa.hiberante.jpaapp.entity;

import org.hibernate.annotations.CreationTimestamp;
import org.hibernate.annotations.UpdateTimestamp;

import javax.persistence.*;
import java.time.LocalDateTime;
import java.util.ArrayList;
import java.util.List;

@Entity
public class Student {

    @Id
    @GeneratedValue
    private Long id;

    @Column(nullable = false)
    private String name;

    //a student can have one passport
    @OneToOne(fetch = FetchType.LAZY)
    private Passport passport;



    //many to many mapping
    @ManyToMany(fetch = FetchType.EAGER)
    @JoinTable(name="STUDENT_COURSE",joinColumns = @JoinColumn(name="STUDENT_ID"),
            inverseJoinColumns = @JoinColumn(name="COURSE_ID"))
    private List<Course> courses=new ArrayList<>();

    public Student(String name) {
        this.name = name;
    }

    public Student(){

        this.name=name;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }

    public Passport getPassport() {
        return passport;
    }

    public void setPassport(Passport passport) {
        this.passport = passport;
    }


    public List<Course> getCourses() {
        return courses;
    }

    public void setCourse(Course course) {
        this.courses.add(course);
    }
}

这两个类通过“多对多”注释进行映射。实际上，起初我在Student.java类中的代码是：

    //many to many mapping
            @ManyToMany
     @JoinTable(name = "STUDENT_COURSE", joinColumns = @JoinColumn(name = "STUDENT_ID")
  private List<Course> courses=new ArrayList<>();

在此阶段，代码已成功编译，我在StudentRepositoryTest.java中使用测试用例获得了结果，

package com.ashwin.jpa.hiberante.jpaapp;

import com.ashwin.jpa.hiberante.jpaapp.entity.Course;
import com.ashwin.jpa.hiberante.jpaapp.entity.Passport;
import com.ashwin.jpa.hiberante.jpaapp.entity.Student;
import com.ashwin.jpa.hiberante.jpaapp.repository.CourseRepository;
import com.ashwin.jpa.hiberante.jpaapp.repository.StudentRepository;
import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.annotation.DirtiesContext;
import org.springframework.test.context.junit4.SpringRunner;

import javax.persistence.EntityManager;
import javax.transaction.Transactional;

@RunWith(SpringRunner.class)
@SpringBootTest
public class StudentRepositoryTest {

 private Logger logger = LoggerFactory.getLogger(this.getClass());

 @Autowired
 private StudentRepository studentRepository;

 @Autowired
 private EntityManager entityManager;



 @Test
 @Transactional
 public void retrieveStudentAndCourses() {
  //many to many mapping
  Student student = entityManager.find(Student.class, 7 L);
  logger.info("student is ->{}", student);

  logger.info("student course is ->{}", student.getCourses());


 }


}

输出为：

 Hibernate: select student0_.id as id1_3_0_, student0_.name as name2_3_0_, student0_.passport_id as passport3_3_0_ from student student0_ where student0_.id=?
    2019-08-01 20:58:38.410 TRACE 18608 --- [           main] o.h.type.descriptor.sql.BasicBinder      : binding parameter [1] as [BIGINT] - [7]
    2019-08-01 20:58:38.464 TRACE 18608 --- [           main] o.h.type.descriptor.sql.BasicExtractor   : extracted value ([name2_3_0_] : [VARCHAR]) - [Mike]
    2019-08-01 20:58:38.466 TRACE 18608 --- [           main] o.h.type.descriptor.sql.BasicExtractor   : extracted value ([passport3_3_0_] : [BIGINT]) - [6]
    2019-08-01 20:58:38.507 TRACE 18608 --- [           main] org.hibernate.type.CollectionType        : Created collection wrapper: [com.ashwin.jpa.hiberante.jpaapp.entity.Student.courses#7]
    2019-08-01 20:58:38.560  INFO 18608 --- [           main] c.a.j.h.jpaapp.StudentRepositoryTest     : student is ->Student{id=7, name='Mike'}
    Hibernate: select courses0_.student_id as student_1_4_0_, courses0_.course_id as course_i2_4_0_, course1_.id as id1_0_1_, course1_.created_date as created_2_0_1_, course1_.local_date_time as local_da3_0_1_, course1_.name as name4_0_1_ from student_course courses0_ inner join course course1_ on courses0_.course_id=course1_.id where courses0_.student_id=?
    Hibernate: select reviewlist0_.course_id as course_i4_2_0_, reviewlist0_.id as id1_2_0_, reviewlist0_.id as id1_2_1_, reviewlist0_.course_id as course_i4_2_1_, reviewlist0_.description as descript2_2_1_, reviewlist0_.rating as rating3_2_1_ from review reviewlist0_ where reviewlist0_.course_id=?
    Hibernate: select reviewlist0_.course_id as course_i4_2_0_, reviewlist0_.id as id1_2_0_, reviewlist0_.id as id1_2_1_, reviewlist0_.course_id as course_i4_2_1_, reviewlist0_.description as descript2_2_1_, reviewlis
2019-08-01 20:58:38.561  INFO 18608 --- [           main] c.a.j.h.jpaapp.StudentRepositoryTest     : student course is ->[Course{id=10001, name='JPA in 50steps'}, Course{id=10002, name='Spring in 50steps'}]

但是当我添加（fetch = FetchType.EAGER）时，如下所示：

//many to many mapping
        @ManyToMany(fetch = FetchType.EAGER)
        @JoinTable(name="STUDENT_COURSE",joinColumns = @JoinColumn(name="STUDENT_ID"),
                inverseJoinColumns = @JoinColumn(name="COURSE_ID"))
        private List<Course> courses=new ArrayList<>();

我得到的错误是：

  
    

org.springframework.beans.factory.BeanCreationException：错误     在类路径中创建名称为“ entityManagerFactory”的bean     资源     [org / springframework / boot / autoconfigure / orm / jpa / HibernateJpaConfiguration.class]：     调用init方法失败；嵌套异常为     javax.persistence.PersistenceException：[每

  
     

原因：org.hibernate.loader.MultipleBagFetchException：无法   同时获取多个袋子：   [com.ashwin.jpa.hiberante.jpaapp.entity.Student.courses，   com.ashwin.jpa.hiberante.jpaapp.entity.Course.reviewList]

0 个答案:

没有答案
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