hibernate 一对多注解开发

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： "font-size:14px;">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 sets = new HashSet(); public Set getSets() { return sets; } public void setSets(Set 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 "font-size:14px;">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） "font-size:14px;">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 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 students=new HashSet(); // 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(); } } }