hibernate 注解

import java.util.Date;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.OneToOne;
import javax.persistence.Table;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.annotations.GenericGenerator;
import org.hibernate.annotations.LazyCollection;
import org.hibernate.annotations.LazyCollectionOption;
import org.springframework.orm.hibernate3.HibernateTemplate;

//在hibernate中，通常配置对象关系映射关系有两种，一种是基于xml的方式，另一种是基于annotation的注解方式，熟话说，萝卜青菜，
//可有所爱，每个人都有自己喜欢的配置方式，我在试了这两种方式以后，发现使用annotation的方式可以更简介，所以这里就简单记录下通过
//annotation来配置各种映射关系，在hibernate4以后已经将annotation的jar包集成进来了，如果使用hibernate3的版本就需要引入annotation的jar包。

//一、单对象操作
@Entity
//如果我们当前这个bean要设置成实体对象，就需要加上Entity这个注解
@Table(name=”t_user”)//设置数据库的表名
public class User{
private int id;
private String username;
private String password;
private Date born;
private Date registerDate;

@Column(name=”register_date”)

// Column中的name属性对应了数据库的该字段名字，里面还有其他属性，例如length，nullable等等
public Date getRegisterDate() {
return registerDate;
}
public void setRegisterDate(Date registerDate){
this.registerDate = registerDate;
}

@Id//定义为数据库的主键ID(建议不要在属性上引入注解，因为属性是private的，如果引入注解会破坏其封装特性，所以建议在getter方法上加入注解)
@GeneratedValue//ID的生成策略为自动生成　　
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public Date getBorn() {
return born;
}
public void setBorn(Date born) {
this.born = born;
}

}

//最后只需要在hibernate.cfg.xml文件里面将该实体类加进去即可：

//

1234

//二、一对多的映射(one-to-many)
//这里我们定义了两个实体类，一个是ClassRoom，一个是Student，这两者是一对多的关联关系。

//ClassRoom类：
@Entity
@Table(name=”t_classroom”)
class ClassRoom{
private int id;
private String className;
private Set students;

public ClassRoom(){
students = new HashSet();
}

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

@Id
@Column(name = “PID”, length = 32)
@GeneratedValue(generator = “generator”)
@GenericGenerator(name = “generator”, strategy = “uuid”)
public int getId(){
return id;
}

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

public String getClassName(){
return className;
}

public void setClassName(String className){
this.className = className;
}

@OneToMany(mappedBy=”room”)

// OneToMany指定了一对多的关系，mappedBy=”room”指定了由多的那一方来维护关联关系，mappedBy指的是多的一方对1的这一方的依赖的属性，
// (注意：如果没有指定由谁来维护关联关系，则系统会给我们创建一张中间表)
@LazyCollection(LazyCollectionOption.EXTRA)
// LazyCollection属性设置成EXTRA指定了当如果查询数据的个数时候，只会发出一条 count(*)的语句，提高性能
public Set getStudents(){
return students;
}

public void setStudents(Set students){
this.students = students;
}

}

@Entity
@Table(name=”t_student”)
class Student{
private int id;
private String name;
private int age;
private ClassRoom room;

@ManyToOne(fetch=FetchType.LAZY)
//ManyToOne指定了多对一的关系，fetch=FetchType.LAZY属性表示在多的那一方通过延迟加载的方式加载对象(默认不是延迟加载)
@JoinColumn(name=”rid”)

// 通过 JoinColumn 的name属性指定了外键的名称 rid　(注意：如果我们不通过JoinColum来指定外键的名称，系统会给我们声明一个名称)
public ClassRoom getRoom(){
return room;
}
public void setRoom(ClassRoom room) {
this.room = room;
}
@Id
@Column(name = “PID”, length = 32)
@GeneratedValue(generator = “generator”)
@GenericGenerator(name = “generator”, strategy = “uuid”)
public int getId() {
return id;
}
public void setId(int id){
this.id = id;
}
public String getName(){
return name;
}
public void setName(String name){
this.name = name;
}
public int getAge(){
return age;
}
public void setAge(int age){
this.age = age;
}

}
//三、一对一映射(One-to-One)
//一对一关系这里定义了一个Person对象以及一个IDCard对象
//Person类：
@Entity
@Table(name=”t_person”)
class Person{
private int id;
private String name;
private IDCard card;

@OneToOne(mappedBy=”person”)

// 指定了OneToOne的关联关系，mappedBy同样指定由对方来进行维护关联关系
public IDCard getCard() {
return card;
}
public void setCard(IDCard card) {
this.card = card;
}
@Id
@Column(name = “PID”, length = 32)
@GeneratedValue(generator = “generator”)
@GenericGenerator(name = “generator”, strategy = “uuid”)
public int getId(){
return id;
}
public void setId(int id){
this.id = id;
}
public String getName(){
return name;
}
public void setName(String name){
this.name = name;
}

}

//IDCard类：
@Entity
@Table(name=”t_id_card”)
class IDCard{
private int id;
private String no;
private Person person;

@Id
@Column(name = “PID”, length = 32)
@GeneratedValue(generator = “generator”)
@GenericGenerator(name = “generator”, strategy = “uuid”)
public int getId(){
return id;
}
public void setId(int id){
this.id = id;
}
public String getNo(){
return no;
}
public void setNo(String no){
this.no = no;
}
@OneToOne

// OnetoOne指定了一对一的关联关系，一对一中随便指定一方来维护映射关系，这里选择IDCard来进行维护
@JoinColumn(name=”pid”)
// 指定外键的名字 pid
public Person getPerson(){
return person;
}
public void setPerson(Person person){
this.person = person;
}
}
//注意:在判断到底是谁维护关联关系时，可以通过查看外键，哪个实体类定义了外键，哪个类就负责维护关联关系。
//四、Many-to-Many映射(多对多映射关系)
//多对多这里通常有两种处理方式，一种是通过建立一张中间表，然后由任一一个多的一方来维护关联关系，另一种就是将多对多拆分成两个一对多的关联关系
//1.通过中间表由任一一个多的一方来维护关联关系
//Teacher类：
@Entity
@Table(name=”t_teacher”)
class Teacher{
private int id;
private String name;
private Set courses;

public Teacher(){
courses = new HashSet();
}
public void addCourse(Course course){
courses.add(course);
}

@Id
@Column(name = “PID”, length = 32)
@GeneratedValue(generator = “generator”)
@GenericGenerator(name = “generator”, strategy = “uuid”)
public int getId(){
return id;
}
public void setId(int id){
this.id = id;
}
public String getName(){
return name;
}
public void setName(String name){
this.name = name;
}
@ManyToMany(mappedBy=”teachers”)

// 表示由Course那一方来进行维护
public Set getCourses(){
return courses;
}
public void setCourses(Set courses){
this.courses = courses;
}

}

//Course类：
@Entity
@Table(name=”t_course”)
class Course{
private int id;
private String name;
private Set teachers;

public Course(){
teachers = new HashSet();
}
public void addTeacher(Teacher teacher){
teachers.add(teacher);
}
@ManyToMany

// ManyToMany指定多对多的关联关系
@JoinTable(name=”t_teacher_course”, joinColumns={ @JoinColumn(name=”cid”)},
inverseJoinColumns={ @JoinColumn(name = “tid”) })
// 因为多对多之间会通过一张中间表来维护两表直接的关系，所以通过 JoinTable 这个注解来声明，name就是指定了中间表的名字，
// JoinColumns是一个 @JoinColumn类型的数组，表示的是我这方在对方中的外键名称，我方是Course，所以在对方外键的名称就是 rid，
// inverseJoinColumns也是一个 @JoinColumn类型的数组，表示的是对方在我这放中的外键名称，对方是Teacher，所以在我方外键的名称就是 tid
public Set getTeachers() {
return teachers;
}

public void setTeachers(Set teachers){
this.teachers = teachers;
}

@Id
@Column(name = “PID”, length = 32)
@GeneratedValue(generator = “generator”)
@GenericGenerator(name = “generator”, strategy = “uuid”)
public int getId(){
return id;
}

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

public String getName(){
return name;
}

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

}
//2.将Many-to-Many拆分成两个One-to-Many的映射(Admin、Role、AdminRole)
//Admin类：
@Entity
@Table(name=”t_admin”)
class Admin{
private int id;
private String name;
private Set ars;
public Admin(){
ars = new HashSet();
}
public void add(AdminRole ar){
ars.add(ar);
}
@Id
@GeneratedValue
public int getId(){
return id;
}
public void setId(int id){
this.id = id;
}
public String getName(){
return name;
}
public void setName(String name){
this.name = name;
}
@OneToMany(mappedBy=”admin”)
// OneToMany关联到了AdminRole这个类，由AdminRole这个类来维护多对一的关系，mappedBy=”admin”
@LazyCollection(LazyCollectionOption.EXTRA)
public Set getArs(){
return ars;
}
public void setArs(Set ars){
this.ars = ars;
}
}
//Role类：
@Entity
@Table(name=”t_role”)
class Role{
private int id;
private String name;
private Set ars;
public Role(){
ars = new HashSet();
}
public void add(AdminRole ar){
ars.add(ar);
}
@Id
@Column(name = “PID”, length = 32)
@GeneratedValue(generator = “generator”)
@GenericGenerator(name = “generator”, strategy = “uuid”)
public int getId(){
return id;
}
public void setId(int id){
this.id = id;
}
public String getName(){
return name;
}
public void setName(String name){
this.name = name;
}
@OneToMany(mappedBy=”role”)
// OneToMany指定了由AdminRole这个类来维护多对一的关联关系，mappedBy=”role”
@LazyCollection(LazyCollectionOption.EXTRA)
public Set getArs(){
return ars;
}
public void setArs(Set ars){
this.ars = ars;
}
}
//AdminRole类：
@Entity
@Table(name=”t_admin_role”)
class AdminRole{
private int id;
private String name;
private Admin admin;
private Role role;
@Id
@Column(name = “PID”, length = 32)
@GeneratedValue(generator = “generator”)
@GenericGenerator(name = “generator”, strategy = “uuid”)
public int getId(){
return id;
}
public void setId(int id){
this.id = id;
}
public String getName(){
return name;
}
public void setName(String name){
this.name = name;
}
@ManyToOne
// ManyToOne关联到Admin
@JoinColumn(name=”aid”)
public Admin getAdmin(){
return admin;
}
public void setAdmin(Admin admin){
this.admin = admin;
}
@ManyToOne
@JoinColumn(name=”rid”)
public Role getRole(){
return role;
}
public void setRole(Role role){
this.role = role;
}
/*通过hibernate来进行插入操作的时候，不管是一对多、一对一还是多对多，都只需要记住一点，在哪个实体类声明了外键，就由哪个类来维护关系，
在保存数据时，总是先保存的是没有维护关联关系的那一方的数据，后保存维护了关联关系的那一方的数据
*/
public void test(){
Session session = new HibernateTemplate().getSessionFactory().openSession();
Transaction transaction=session.beginTransaction();
Person p = new Person();
p.setName(“xiaoluo”);
session.save(p);

IDCard card = new IDCard();card.setNo("1111111111");card.setPerson(p);session.save(card);transaction.commit();session.close();

}

}