Spring-Hibernate，多对多关系查询

Question

我有两个bean类Student和Course，它们之间有很多关系。 例如。 一个学生可以注册多个课程，反之亦然。 我已经使用HibernateTemplate将对象保存到Oracle DB中。 以下是学生，课程和StudentDao课程。

学生班

package com.springhibernate;

import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

@Entity
@Table(name="Student")

public class Student {
    private int studentId;
    private String firstName;
    private String lastName;
    private Set<Course> courses;

@Id
@Column(name="student_id")
public int getStudentId() {
    return studentId;
}
public void setStudentId(int studentId) {
    this.studentId = studentId;
}

@Column(name="first_name")
public String getFirstName() {
    return firstName;
}
public void setFirstName(String firstName) {
    this.firstName = firstName;
}

@Column(name="last_name")
public String getLastName() {
    return lastName;
}
public void setLastName(String lastName) {
    this.lastName = lastName;
}

@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name = "Student_Course", joinColumns = @JoinColumn(name = "student_id"), inverseJoinColumns = @JoinColumn(name = "course_id"))
public Set<Course> getCourses() {
    return courses;
}
public void setCourses(Set<Course> courses) {
    this.courses = courses;
}

}

学生道课

package com.springhibernate;

import java.util.List;

import org.springframework.orm.hibernate3.HibernateTemplate;

public class StudentDao {

private static Helper helper = new Helper();

HibernateTemplate template;
public void setTemplate(HibernateTemplate template) {
    this.template = template;
}

// method to save student
public void saveStudent(Student s) {
    template.save(s);
}

// method to return one employee of given id
public Student getById(int id) {
    Student s = (Student) template.get(Student.class, id);
    return s;
}

public List<Course> findCourse(){
    List<Course> list = template.find("from Course");
    return list;
}
}

课程课程

package com.springhibernate;

import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;


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

private int courseId;
private String courseName;
private Set<Student> students;

@Id
@Column(name="course_id")
public int getCourseId() {
    return courseId;
}
public void setCourseId(int courseId) {
    this.courseId = courseId;
}

@Column(name="course_name")
public String getCourseName() {
    return courseName;
}
public void setCourseName(String courseName) {
    this.courseName = courseName;
}

@ManyToMany(cascade=CascadeType.ALL,mappedBy="courses")
public Set<Student> getStudents() {
    return students;
}
public void setStudents(Set<Student> students) {
    this.students = students;
}

@Override
public int hashCode() {
    // TODO Auto-generated method stub
    return this.courseId;
}

@Override
public boolean equals(Object o) {
    // TODO Auto-generated method stub
    Course temp = (Course) o;
    return (this.courseId==temp.courseId);

}
}

我有以下两个查询

1. 我能够成功将数据保存在student_course表中。 我想知道我是否要从student_course表中检索数据，如何使用HibernateTemplate进行处理，或者还有其他方法可以这样做？ 例如，查询就像

    select course_id from student_course where student_id=1 

   请注意，我只希望课程ID列不完整。

2. 如果我要在student_course表中再增加一列，例如course_name（来自课程表），该怎么办？

Answer 1

您可以通过以下方式进行操作，但是请记住，HibernateTemplate是一个旧的API，您应该使用EntityManager（Factory）。 您可以通过Peristence类获得它。

hibernateTemplate.execute(new HibernateCallback<List>() {

    public String doInHibernate(Session s)
            throws HibernateException, SQLException {
        SQLQuery sql=s.createSQLQuery("select course_id from student_course where student_id=?");
            sql.setParameter(0, adventureId);
        sql.addScalar(studentID);
        return sql.list();
    }
});