java - hibernate 中的多对多

Question

我是 hibernate 的新手。我有三张 table (类(class)-学生-类(class)学生)。以下是我的代码，但没有用。我也写了 cfg.xml。我认为我的问题是我的 hbm 文件，但我无法解决。

public class Student {
private int student_id;
private String student_name;
public Student()
{

}
public Student(int id,String name)
{
this.student_id=id;
this.student_name=name;
}
private Set<Course> courses = new HashSet<Course>();
public int getstudentid()
{
    return student_id;
}
public void setstudentid(int id)

{
    this.student_id=id;
}
public String getstudentname()
{
    return student_name;
}
public void setstudentname(String name)
{
    this.student_name=name;
}
public Set<Course> getcourse()
{
    return courses;
}
public void setcourse(Set<Course> courses)
{
    this.courses=courses;
}
}

public class Course {
    private int course_id;
    private String course_name;
    private Set<Student> students= new HashSet<Student>();
public Course()
{

}
public Course(int id, String name)
{
    this.course_id=id;
    this.course_name=name;
}
public int getcourseid()
{
    return course_id;
}
public void setcourseid(int id)
{
    this.course_id=id;
}
public String getcoursename()
{
    return course_name;
}
public void setcoursename(String name)
{
    this.course_name=name;
}
public Set<Student> getstudents()
{
    return students;
}
public void setstudents(Set<Student> students)
{
    this.students=students;
}
}

hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated May 29, 2012 3:19:54 PM by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping package="first">
    <class name="Course" table="COURSE">
        <id name="course_id" type="int" access="field">
            <column name="COURSE_ID" />
            <generator class="assigned" />
        </id>
        <property name="course_name" type="java.lang.String" access="field">
            <column name="COURSE_NAME" />
        </property>
        <set name="students" table="student_course"
inverse="false" lazy="true" fetch="join" cascade="all">
<key column="student_id" />
<many-to-many column="course_id" class="Course" />
</set>
    </class>
</hibernate-mapping>

和

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated May 29, 2012 3:19:54 PM by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping package="first">
    <class name="Student" table="STUDENT">
        <id name="student_id" type="int" access="field">
            <column name="STUDENT_ID" />
            <generator class="assigned" />
        </id>
        <property name="student_name" type="java.lang.String" access="field">
            <column name="STUDENT_NAME" />
        </property>
        <set name="courses" table="student_course"
inverse="false" lazy="true" fetch="join" cascade="all">
<key column="student_id" />
<many-to-many column="course_id" class="Course" />
</set>
    </class>
</hibernate-mapping>

我的托管代码:

public class ManageStudent {
    private static SessionFactory sf;
    private static ServiceRegistry serviceRegistry;

    public static void main(String[] args) {
    try {
    Configuration configuration = new Configuration().addResource("first/Student.hbm.xml").addResource("first/Course.hbm.xml");
    configuration.configure();
    serviceRegistry = new ServiceRegistryBuilder().applySettings(
    configuration.getProperties()).buildServiceRegistry();
    sf = configuration.buildSessionFactory(serviceRegistry);
    } catch (Throwable ex) {
    System.err.println("Failed to create sessionFactory object." + ex);
    throw new ExceptionInInitializerError(ex);
    }


    System.out.println("Hibernate Many to Many Mapping Example Using Xml ");

    Session session = sf.openSession();
    session.beginTransaction();

    Student s1=new Student(1,"mina");
    Student s2=new Student(2,"samira");

    Course c1=new Course(10,"math");
    Course c2=new Course(11,"sport");

    s1.getcourse().add(c2);
    s2.getcourse().add(c1);
    s2.getcourse().add(c2);

    session.save(s1);
    session.save(s2);

    session.getTransaction().commit();
    session.close();
    }
}

我的错误是:

Failed to create sessionFactory object.org.hibernate.MappingException: Could not get constructor for org.hibernate.persister.entity.SingleTableEntityPersister

Exception in thread "main" java.lang.ExceptionInInitializerError
    at first.ManageStudent.main(ManageStudent.java:21)
Caused by: org.hibernate.MappingException: Could not get constructor for org.hibernate.persister.entity.SingleTableEntityPersister
    at org.hibernate.persister.internal.PersisterFactoryImpl.create(PersisterFactoryImpl.java:180)
    at org.hibernate.persister.internal.PersisterFactoryImpl.createEntityPersister(PersisterFactoryImpl.java:131)
    at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:346)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1737)
    at first.ManageStudent.main(ManageStudent.java:18)
Caused by: org.hibernate.HibernateException: Unable to instantiate default tuplizer [org.hibernate.tuple.entity.PojoEntityTuplizer]
    at org.hibernate.tuple.entity.EntityTuplizerFactory.constructTuplizer(EntityTuplizerFactory.java:138)
    at org.hibernate.tuple.entity.EntityTuplizerFactory.constructDefaultTuplizer(EntityTuplizerFactory.java:188)
    at org.hibernate.tuple.entity.EntityMetamodel.<init>(EntityMetamodel.java:336)
    at org.hibernate.persister.entity.AbstractEntityPersister.<init>(AbstractEntityPersister.java:498)
    at org.hibernate.persister.entity.SingleTableEntityPersister.<init>(SingleTableEntityPersister.java:142)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at org.hibernate.persister.internal.PersisterFactoryImpl.create(PersisterFactoryImpl.java:158)
    ... 4 more
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at org.hibernate.tuple.entity.EntityTuplizerFactory.constructTuplizer(EntityTuplizerFactory.java:135)
    ... 13 more
Caused by: org.hibernate.PropertyNotFoundException: Could not find a getter for courses in class first.Student
    at org.hibernate.property.BasicPropertyAccessor.createGetter(BasicPropertyAccessor.java:316)
    at org.hibernate.property.BasicPropertyAccessor.getGetter(BasicPropertyAccessor.java:310)
    at org.hibernate.mapping.Property.getGetter(Property.java:298)
    at org.hibernate.tuple.entity.PojoEntityTuplizer.buildPropertyGetter(PojoEntityTuplizer.java:436)
    at org.hibernate.tuple.entity.AbstractEntityTuplizer.<init>(AbstractEntityTuplizer.java:200)
    at org.hibernate.tuple.entity.PojoEntityTuplizer.<init>(PojoEntityTuplizer.java:82)
    ... 18 more

请帮我。
我的新错误:

Failed to create sessionFactory object.org.hibernate.HibernateException: Wrong column type in SYSTEM.COURSE for column COURSE_NAME. Found: number, expected: varchar2(255 char)
Exception in thread "main" java.lang.ExceptionInInitializerError
    at first.ManageStudent.main(ManageStudent.java:21)
Caused by: org.hibernate.HibernateException: Wrong column type in SYSTEM.COURSE for column COURSE_NAME. Found: number, expected: varchar2(255 char)
    at org.hibernate.mapping.Table.validateColumns(Table.java:282)
    at org.hibernate.cfg.Configuration.validateSchema(Configuration.java:1268)
    at org.hibernate.tool.hbm2ddl.SchemaValidator.validate(SchemaValidator.java:155)
    at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:453)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1737)
    at first.ManageStudent.main(ManageStudent.java:18)

Answer 1

从代码片段中，我可以看到一件事是错误的:

<class name="rStudent" table="STUDENT">当类(class)名称为 Student 时，更改此设置并重新运行。

当 hibernate 没有找到 No Arg Constructor 或者你有循环依赖时，通常会抛出这个异常，因为在你的代码中我看到 No Arg 构造函数可用，并且对于初始化不存在循环依赖，更正名称应该有助于解决这个问题。

根据编辑:

您的类(class)的 getter、setter 不正确

代替

public Set<Course> getcourse() // this should be getCourses
{
    return courses;
}
public void setcourse(Set<Course> courses) // this should be setCourses
{
    this.courses=courses;
}

在类似的行上，请在您的 Courses.java 中更改以下内容

public Set<Student> getstudents() // Make it getStudents
{
    return students;
}
public void setstudents(Set<Student> students) // Make it setStudents
{
    this.students=students;
}

您的 getter、setter 不遵循 hibernate 所需的正确命名约定。

使用以下代码检查学生的 getter、setter:

import java.util.HashSet;
import java.util.Set;

public class Student {

    private int    student_id;
    private String  student_name;
    private Set<Course> courses = new HashSet<Course>();
    public Student() {

    }
    public Student(int id, String name) {
        this.student_id = id;
        this.student_name = name;
    }

    /**
     * @return the student_id
     */
    public int getStudent_id() {
        return student_id;
    }

    /**
     * @param student_id the student_id to set
     */
    public void setStudent_id(int student_id) {
        this.student_id = student_id;
    }

    /**
     * @return the student_name
     */
    public String getStudent_name() {
        return student_name;
    }

    /**
     * @param student_name the student_name to set
     */
    public void setStudent_name(String student_name) {
        this.student_name = student_name;
    }

    /**
     * @return the courses
     */
    public Set<Course> getCourses() {
        return courses;
    }

    /**
     * @param courses the courses to set
     */
    public void setCourses(Set<Course> courses) {
        this.courses = courses;
    }
}

类(class)类似

import java.util.HashSet;
import java.util.Set;

public class Course {
    private int          course_id;
    private String       course_name;
    private Set<Student>    students    = new HashSet<Student>();
    public Course() {

    }
    public Course(int id, String name) {
        this.course_id = id;
        this.course_name = name;
    }

    /**
     * @return the course_id
     */
    public int getCourse_id() {
        return course_id;
    }

    /**
     * @param course_id the course_id to set
     */
    public void setCourse_id(int course_id) {
        this.course_id = course_id;
    }

    /**
     * @return the course_name
     */
    public String getCourse_name() {
        return course_name;
    }

    /**
     * @param course_name the course_name to set
     */
    public void setCourse_name(String course_name) {
        this.course_name = course_name;
    }

    /**
     * @return the students
     */
    public Set<Student> getStudents() {
        return students;
    }

    /**
     * @param students the students to set
     */
    public void setStudents(Set<Student> students) {
        this.students = students;
    }
}