Hibernate的学习总结(复合主键)

当表存在复合主键时，Hibernate对其的处理稍微复杂一些。

1.POJO类得实现Serializable接口

2.POJO类得重写equals()方法和hashCode()方法

3.hbm文件中用<composite-id>节点配置复合主键信息

其中重写equals()方法和hashCode()方法可以使用commons-lang包来简化处理

以下是一个小例子：

import java.io.Serializable;

import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;

public class Person implements Serializable {
private String name;

private String phone;

private int age;

public boolean equals(Object obj) {
// TODO 自动生成方法存根
if (this == obj) {
return true;
}
if (!(obj instanceof Person)) {
return false;
}
Person p = (Person) obj;
return new EqualsBuilder().append(this.name, p.name).append(this.phone,
p.phone).append(this.age, p.age).isEquals();
}

public int hashCode() {
// TODO 自动生成方法存根
return new HashCodeBuilder().append(this.name).append(this.age).append(
this.phone).toHashCode();
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public String getPhone() {
return phone;
}

public void setPhone(String phone) {
this.phone = phone;
}

public String getName() {
return name;
}

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

}

其hbm配置文件代码为：

<?xml version="1.0" encoding='UTF-8'?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >

<!-- DO NOT EDIT: This is a generated file that is synchronized -->
<!-- by MyEclipse Hibernate tool integration.                   -->
<!-- Created Sat Nov 11 21:30:08 CST 2006                         -->
<hibernate-mapping package="org.lxh.hibernate02">

<class name="Person" table="PERSON">
<composite-id>
<key-property name="name" column="NAME" type="string"/>
<key-property name="phone" column="PHONE" type="string"/>
</composite-id>
<property name="age" column="AGE" type="int" />
</class>

</hibernate-mapping>

还有一种更好的方式是，将复合主键部分单独提出一个POJO类

person类

import java.io.Serializable;

import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;

public class Person implements Serializable {

private PersonKey id ;
private int age;
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public PersonKey getId() {
return id;
}
public void setId(PersonKey id) {
this.id = id;
}

}

PersonKey类

/*
* WARNING: DO NOT EDIT THIS FILE. This is a generated file that is synchronized
* by MyEclipse Hibernate tool integration.
*
* Created Sat Nov 11 21:36:22 CST 2006 by MyEclipse Hibernate Tool.
*/
package org.lxh.hibernate03;

import java.io.Serializable;

import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;

/**
* A class representing a composite primary key id for the PERSON
* table.  This object should only be instantiated for use with instances
* of the Person class.
* WARNING: DO NOT EDIT THIS FILE. This is a generated file that is synchronized
* by MyEclipse Hibernate tool integration.
*/
public class PersonKey
implements Serializable
{
/** The cached hash code value for this instance.  Settting to 0 triggers re-calculation. */
private volatile int hashValue = 0;

/** The value of the NAME component of this composite id. */
private java.lang.String name;

/** The value of the PHONE component of this composite id. */
private java.lang.String phone;

/**
* Simple constructor of PersonKey instances.
*/
public PersonKey()
{
}

/**
* Returns the value of the name property.
* @return java.lang.String
*/
public java.lang.String getName()
{
return name;
}

/**
* Sets the value of the name property.
* @param name
*/
public void setName(java.lang.String name)
{
hashValue = 0;
this.name = name;
}

/**
* Returns the value of the phone property.
* @return java.lang.String
*/
public java.lang.String getPhone()
{
return phone;
}

/**
* Sets the value of the phone property.
* @param phone
*/
public void setPhone(java.lang.String phone)
{
hashValue = 0;
this.phone = phone;
}

/**
* Implementation of the equals comparison on the basis of equality of the id components.
* @param rhs
* @return boolean
*/
public boolean equals(Object obj)
{
if (this == obj) {
return true;
}
if (!(obj instanceof Person)) {
return false;
}
PersonKey p = (PersonKey) obj;
return new EqualsBuilder().append(this.name, p.getName()).append(this.phone,
p.getPhone()).isEquals();
}

/**
* Implementation of the hashCode method conforming to the Bloch pattern with
* the exception of array properties (these are very unlikely primary key types).
* @return int
*/
public int hashCode()
{
return new HashCodeBuilder().append(this.name).append(
this.phone).toHashCode();
}
}

hbm文件

<?xml version="1.0" encoding='UTF-8'?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >

<!-- DO NOT EDIT: This is a generated file that is synchronized -->
<!-- by MyEclipse Hibernate tool integration.                   -->
<!-- Created Sat Nov 11 21:36:21 CST 2006                         -->
<hibernate-mapping package="org.lxh.hibernate03">

<class name="Person" table="PERSON">
<composite-id name="id" class="PersonKey"> <!-- 加上复合主键类的类名 -->
<key-property name="name" column="NAME" type="string"/>
<key-property name="phone" column="PHONE" type="string"/>
</composite-id>

<property name="age" column="AGE" type="int" />
</class>

</hibernate-mapping>