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hibernate之关于关联映射的综合应用
@Entity
@Table(name="c_course")
public class Course {
private Integer id;
private String coursename;
private Set<Student> students=new HashSet<Student>();
private Set<Score> scores=new HashSet<Score>();
@OneToMany(mappedBy="course")//必须指定关系由多的一方维护
public Set<Score> getScores() {
return scores;
}
public void setScores(Set<Score> scores) {
this.scores = scores;
}
@ManyToMany//指定中间表是s_score
@JoinTable(name="s_score",joinColumns={@JoinColumn(name="course_id")},
inverseJoinColumns={@JoinColumn(name="student_id")})
public Set<Student> getStudents() {
return students;
}
public void setStudents(Set<Student> students) {
this.students = students;
}
@Id
@GeneratedValue
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
@Column(name="c_coursename")
public String getCoursename() {
return coursename;
}
public void setCoursename(String coursename) {
this.coursename = coursename;
}
}(课程表Course)@Entity
@Table(name="t_student")
public class Student {
private Integer id;
private String name;
private Set<Course> courses=new HashSet<Course>();
private Set<Score> scores=new HashSet<Score>();
@OneToMany(mappedBy="student")
public Set<Score> getScores() {
return scores;
}
public void setScores(Set<Score> scores) {
this.scores = scores;
}
@ManyToMany
@JoinTable(name="s_score",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;
}
@Id
@GeneratedValue
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
@Column(name="s_name")
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}(Student学生表)@Entity
@Table(name="s_score")
public class Score {
private Integer id;
private String score;
private Student student;
private Course course;
@ManyToOne(cascade={CascadeType.ALL})//配置级联操作
@JoinColumn(name="student_id")
public Student getStudent() {
return student;
}
public void setStudent(Student student) {
this.student = student;
}
@ManyToOne(cascade={CascadeType.ALL})
@JoinColumn(name="course_id")
public Course getCourse() {
return course;
}
public void setCourse(Course course) {
this.course = course;
}
@Id
@GeneratedValue
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
@Column(name="s_score")
public String getScore() {
return score;
}
public void setScore(String score) {
this.score = score;
}
}(分数表，也是中间关联表，Score)那么问题来了，采用Hibernate自动建表，我们看一下建表语句
12:11:08,169 DEBUG SchemaExport:415 -
create table c_course (
id integer not null auto_increment,
c_coursename varchar(255),
primary key (id)
)
12:11:08,333 DEBUG SchemaExport:415 -
create table s_score (
id integer not null,
s_score varchar(255),
course_id integer,
student_id integer not null auto_increment,
primary key (student_id, course_id)
)
12:11:08,455 DEBUG SchemaExport:415 -
create table t_student (
id integer not null auto_increment,
s_name varchar(255),
primary key (id)
) @Test
public void add(){
try {
Configuration cfg=new Configuration();
cfg.configure();
SessionFactory sessionFactory=cfg.buildSessionFactory();
Session session=sessionFactory.openSession();
session.beginTransaction();
Student student1=new Student();
student1.setName("张三1");
// Student student2=new Student();
// student2.setName("李四");
Course c1=new Course();
c1.setCoursename("数学1");
Course c2=new Course();
c2.setCoursename("语文1");
// session.save(student1);
// session.save(c1);
// session.save(student2);
// session.save(c2);
Score score=new Score();
score.setScore("901");
score.setCourse(c1);
score.setStudent(student1);
//张三数学90分
session.save(score);
Score score2=new Score();
score2.setCourse(c2);
score2.setScore("100");
score2.setStudent(student1);
session.save(score2);
session.getTransaction().commit();
session.close();
sessionFactory.close();
} catch (HibernateException e) {
e.printStackTrace();
}
}ok，大家可以看出，为什么我们最后只需要保存score就行呢？没有session.save()student和course,为什么也能直接保存数据库中？这就是
cascade={CascadeType.ALL}public void findTest(){
Configuration cfg=new Configuration();
cfg.configure();
SessionFactory sessionFactory=cfg.buildSessionFactory();
Session s=sessionFactory.openSession();
s.beginTransaction();
Student student=(Student)s.load(Student.class, 2);
System.out.println("学生姓名"+student.getName());
for(Course course:student.getCourses()){
System.out.print("--------"+"课程名称"+course.getCoursename());
for(Score score:course.getScores()){
System.out.println("--------"+"课程分数"+score.getScore());
}
}
s.getTransaction().commit();
s.close();
sessionFactory.close();
}public void update(){
Configuration cfg=new Configuration();
cfg.configure();
SessionFactory sessionFactory=cfg.buildSessionFactory();
Session s=sessionFactory.openSession();
s.beginTransaction();
Student student=(Student)s.load(Student.class,1);
//我们现在把查询出来语文成绩改为0分
for(Course course:student.getCourses()){
System.out.println(course.getCoursename());
if("语文".equals(course.getCoursename())){
for(Score score:course.getScores()){
if(score.getStudent().getId().equals(student.getId())){
score.setScore("0");
s.update(score);
}
}
}
}
s.getTransaction().commit();
s.close();
sessionFactory.close();
}@Test
public void deleteObj(){
Configuration cfg=new Configuration();
cfg.configure();
SessionFactory sessionFactory=cfg.buildSessionFactory();
Session s=sessionFactory.openSession();
s.beginTransaction();
Student student=(Student)s.load(Student.class,3);
s.delete(student);
s.getTransaction().commit();
s.close();
sessionFactory.close();
}hibernate之关于关联映射的综合应用
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