Question

我刚刚开始学习Hibernate，我只是通过书中的示例，并且有一些奇怪的与ManyToMany关系的例子，这里是代码：

关系的左侧

package com.examscm.mappings;

import com.examscm.HibernateUtil;
import org.hibernate.Session;

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

/**
* Created by me on 20.06.15.
*/

@Entity
@Table(schema = "HibernateBook")
public class LeftManyStudents {

private long id;
private String studentName;
List<RightManyCourses> courses = new ArrayList<>();

@Id
@GeneratedValue
public long getId() {
    return id;
}

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

public String getStudentName() {
    return studentName;
}

public void setStudentName(String studentName) {
    this.studentName = studentName;
}

@ManyToMany(targetEntity = RightManyCourses.class, cascade = CascadeType.ALL)
@JoinTable(name = "join_table", schema = "HibernateBook",
        joinColumns = { @JoinColumn(name = "lmstudent_id")},
        inverseJoinColumns = {@JoinColumn(name = "rmcourse_id")})
public List<RightManyCourses> getCourses(){
    return courses;
}

public void setCourses(List<RightManyCourses> courses){
    this.courses = courses;
}

public static void main(String[] args){
    HibernateUtil.recreateDatabase();
    /*Creating and saving instances of left and right side
      side of relationship*/
}
}

关系的右侧：

package com.examscm.mappings;

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

/**
* Created by me on 20.06.15.
*/

@Entity
@Table(schema = "HibernateBook")
public class RightManyCourses {

private long id;
private String courseCode;
List<LeftManyStudents> students = new ArrayList<>();

@Id
@GeneratedValue
public long getId() {
    return id;
}

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

public String getCourseCode() {
    return courseCode;
}

public void setCourseCode(String courseCode) {
    this.courseCode = courseCode;
}

@ManyToMany(targetEntity = LeftManyStudents.class,
cascade = CascadeType.ALL)
@JoinTable(name = "join_table", schema = "HibernateBook",
joinColumns = { @JoinColumn(name = "rmcourse_id")},
inverseJoinColumns = {@JoinColumn(name = "lmstudent_id")}
)
public List<LeftManyStudents> getStudents() {
    return students;
}

public void setStudents(List<LeftManyStudents> students){
    this.students = students;
}
}

重新创建数据库代码：

public static void recreateDatabase(){
    Configuration configuration = getInitializedConfiguration();
    new SchemaExport(configuration).create(true, true);
}

问题是，当存在默认的Class to Column name映射时，everythink工作正常，但当我更改它时，例如：

@Table(name = "left_many_students", schema = "HibernateBook")
@Table(name = "right_many_courses", schema = "HibernateBook")

我收到了以下错误

cze 20, 2015 10:21:59 PM org.hibernate.tool.hbm2ddl.SchemaExport perform
ERROR: Table 'HibernateBook.join_table' doesn't exist

所以我手动创建它然后下一个错误：

cze 20, 2015 10:23:50 PM org.hibernate.tool.hbm2ddl.SchemaExport perform
ERROR: HHH000389: Unsuccessful: alter table HibernateBook.join_table drop foreign key FK_22m6gyyey9mu21mlfbge6uguj
cze 20, 2015 10:23:50 PM org.hibernate.tool.hbm2ddl.SchemaExport perform
ERROR: Can't DROP 'FK_22m6gyyey9mu21mlfbge6uguj'; check that column/key exists
cze 20, 2015 10:23:50 PM org.hibernate.tool.hbm2ddl.SchemaExport perform
ERROR: HHH000389: Unsuccessful: alter table HibernateBook.player drop foreign key FK_5q11flfd61t4n9eepixi8ltup
cze 20, 2015 10:23:50 PM org.hibernate.tool.hbm2ddl.SchemaExport perform
ERROR: Can't DROP 'FK_5q11flfd61t4n9eepixi8ltup'; check that column/key exists

但这真的很奇怪，因为如果我只是从这两个段落中移除@Entity并重新创建数据库，那么每个方面都可以正常工作，没有外键错误。

我不知道问题是什么，有人能告诉我吗？

Hibernate ManyToMany通过连接表

0 个答案: