学步园

 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。

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;

数据库 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;

}

}