hibernate 注解配置一对多关系简单实例

hibernate 注解配置一对多关系

     从Hibernate 2.5开始就可以使用annotation实现实体关系的映射了，减少了配置hbm文件的繁琐，而且annotation也是一种趋势，现在的SSH2的整合都是完全可以用annotation来实现。在以前实现一对多关联的关联式都是使用hbm文件，今天我们来使用annotation试试，同样也能实现其功能。

1.数据库：oracle数据库，有person和address二张表，一对多的关系。

数据库：

create table person        (                id number(4) not null,                uname varchar (20)        );        create table address                (                        id number(4) not null,                address varchar(20) not null,                personId number(4) not null        )        alter table person        add constraint primary_id parmary key(id)        deferrable initially deferred;

2.Person实体类：

package com.zengguo.po;import java.io.Serializable;import java.util.HashSet;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.OneToMany;import javax.persistence.Table;import org.hibernate.annotations.Fetch;import org.hibernate.annotations.FetchMode;import org.hibernate.annotations.GenericGenerator;import org.hibernate.annotations.Parameter;@SuppressWarnings(“serial”)@Entity@Table(name = “person”)public class Person implements Serializable {//oracle 序列@Id@GenericGenerator(name = “personGenericGenerator”, strategy = “sequence”,parameters = { @Parameter(value = “hibernate_seq”, name = “sequence”) })@GeneratedValue(generator=”personGenericGenerator”)private long id;@Column(name=”uname”)private String uname;@OneToMany(targetEntity=Address.class,cascade=CascadeType.ALL)@Fetch(FetchMode.JOIN)//updatable=false很关键，如果没有它，在级联删除的时候就会报错(反转的问题)@JoinColumn(name=”personId”,updatable=false)private Set<Address> sets = new HashSet<Address>();public Set<Address> getSets() {return sets;}public void setSets(Set<Address> sets) {this.sets = sets;}public Person() {super();}public long getId() {return id;}public void setId(long id) {this.id = id;}public String getUname() {return uname;}public void setUname(String uname) {this.uname = uname;}}

3.Address实体类

package com.zengguo.po;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.ManyToOne;import javax.persistence.Table;import org.hibernate.annotations.GenericGenerator;import org.hibernate.annotations.Parameter;@SuppressWarnings(“serial”)@Entity@Table(name = “address”)public class Address implements java.io.Serializable {//使用序列生成主键@Id@GenericGenerator(name = “addressGenericGenerator”, strategy = “sequence”,parameters = { @Parameter(value = “hibernate_seq”, name = “sequence”) })@GeneratedValue(generator = “addressGenericGenerator”)private long id;@Column(name = “address”)private String address;//多对一，@JoinColumn与@column类似，指定映射的数据库字段@ManyToOne(targetEntity = Person.class)@JoinColumn(name=”personId”,updatable=false)private Person person;public Address() {super();}public long getId() {return id;}public void setId(long id) {this.id = id;}public String getAddress() {return address;}public void setAddress(String address) {this.address = address;}public Person getPerson() {return person;}public void setPerson(Person person) {this.person = person;}}

hibernate一对多mappedBy的用法：（班级classes和学生student，一对多的关系）

package oneToMany; import java.util.Set; import javax.persistence.*; /* 注意导入时，是导入：import javax.persistence.*;    非导入org.hibernate的相关类：import org.hibernate.annotations.Entity; */ @Entity @Table(name="classes") public class Classes implements Serializable {   @Id   @GeneratedValue(strategy=GenerationType.AUTO)   private int id;   private String name;       @OneToMany(cascade=CascadeType.ALL,mappedBy="classes")      private Set<Student> students; //getter,setter省略 } package oneToMany; import javax.persistence.*; @Entity @Table(name="student") public class Student implements Serializable  {   @Id   @GeneratedValue(strategy=GenerationType.AUTO)   private int sid;       private String sname;       //若有多个cascade，可以是：{CascadeType.PERSIST,CascadeType.MERGE}   @ManyToOne(cascade={CascadeType.ALL})           @JoinColumn(name="classid")     //student类中对应外键的属性：classid   private Classes classes; //getter,setter省略 } public class TestOneToMany { /* CREATE TABLE    student (    --要定义外键!!!!!!!     `sid` double NOT NULL auto_increment,     `classid` double NULL,     `sname` varchar(255) NOT NULL,     PRIMARY KEY    (sid),     INDEX par_ind (classid),     FOREIGN KEY (classid) REFERENCES classes(id) ON DELETE CASCADE ON UPDATE CASCADE ) ENGINE=InnoDB */      public static void main(String[] args) throws SQLException      {     try     {       SessionFactory sf = new AnnotationConfiguration().configure().buildSessionFactory();       Session session=sf.openSession();       Transaction tx=session.beginTransaction();         /*因为mappedBy是定义在classes中,即classes类不负责维护级联关系.即维护者是student.所以,1.要将clsses的数据,赋给student,即用student的setClasses()方法去捆定class数据;2.在进行数据插入/更新session.save()/session.update()时,最后操作的是student.*/      Classes classes=new Classes();       classes.setName("access");               Student st1=new Student();       st1.setSname("jason");       st1.setClasses(classes);       session.save(st1);               Student st2=new Student();       st2.setSname("hwj");       st2.setClasses(classes);       session.save(st2);       tx.commit();/* 输出如下:Hibernate: insert into classes (name) values (?)Hibernate: insert into student (classid, sname) values (?, ?)Hibernate: insert into student (classid, sname) values (?, ?)*//*因为一端维护关系另一端不维护关系的原因，我们必须注意避免在应用中用不维护关系的类(class)建立关系，因为这样建立的关系是不会在数据库中存储的。如上的代码倒过来,则插入时,student的外键值为空.如下:*///      Student st1=new Student(); //      st1.setSname("jason"); //      session.save(st1); //        //      Student st2=new Student(); //      st2.setSname("hwj"); //      session.save(st2); //        //      Set<Student> students=new HashSet<Student>(); //      students.add(st1); //      students.add(st2); //        //      Classes classes=new Classes(); //      classes.setName("access"); //      classes.setStudents(students); //      session.save(classes); /*输出如下:Hibernate: insert into student (classid, sname) values (?, ?)Hibernate: insert into student (classid, sname) values (?, ?)Hibernate: insert into classes (name) values (?)*/    }     catch(HibernateException e)     {       e.printStackTrace();            }   } }