三、ORM(Object/Relational Mapper)---Hibernate对象映射

一. ORM(Object/Relational Mapper)

1. OR映射---Hibernate基本数据类型

Hibernate基本类型	Java类型	标准SQL字段类型
boolean	boolean, java.lang.Boolean	BIT
yes_no	boolean, java.lang.Boolean	CHAR(1) ( 'Y'/'N')
true_false	boolean, java.lang.Boolean	CHAR(1) ( 'Y'/'N')
byte	byte, java.lang.Byte	TINYINT
short	short, java.lang.Short	SMALLINT
integer	int, java.lang.Integer	INTEGER
long	long, java.lang.Long	BIGINT
float	float, java.lang.Float	FLOAT
double	double, java.lang.Double	DOUBLE
big_decimal	java.math.BigDecimal	NUMBERIC
character	java.lang.String	CHAR(1)
string	java.lang.String	VARCHAR
date	java.util.Date, java.sql.Date	DATE
time	java.util.Date, java.sql.Time	TIME
timestamp	java.util.Date, java.sql.TimeStamp	TIMESTAMP
calendar	java.util.Calendar	TIMESTAMP
calendar_date	java.util.Calendar	Date
clob	java.sql.Clob	CLOB
blob	java.sql.Blob	BLOB
binary	byte[]	VARBINARY, BLOB
text	java.lang.String	CLOB
seralizable	java.io.Serializable	VARBINARY, BLOB
class	java.lang.Class	VARCHAR
local	java.util.Locale	VARCHAR
timezone	java.util.TimeZone	VARCHAR
currency	java.util.Currency	VARCHAR

2. OR映射---实体映射示例

*.hbm.xml, 主体内容包含表/类映射, id映射, 属性字段映射三个部分.示例文件:

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

XML文件头定义了文件的编码方式, DTD与Hibernate的版本有关, 上面是使用hibernate 3.x使用的DTD.

3. OR映射---表/类映射

name: 指定了Java数据封装的POJO类类型.

table: 指定了数据库的表名

4. OR映射---id映射

name: 指定了映射POJO类的属性名,

type: POJO类中属性的数据类型;

column: 数据库表的主键字段;

generator子元素:由其class属性指定主键生成方式:

• assigned: 主键由应用程序产生, 不需要hibernate干预
• identity: 使用数据库的主键生成机制, 如MySQL, DB2、SQL Server的自增主键.
• sequence: 使用数据库的sequence机制, 如Oracle的sequence
• uuid.hex: 由Hibernate基于128位唯一值产生算法, 根据ip, 时间, jvm启动时间, 内部自增量生成十六进制的数值, 编码后成为一个32位长的字符串. 该方法提供了最好的数据库插入性能和数据库平台适应性.
• uuid.string: 与uuid.hex类似, 只是生成的主键没有进行编码, 只有16位长度. 在某些数据库可能出错.
• hilo: 通过hilo算法实现主键生成, 需要额外的数据库表保存主键生成历史状态.
• seqhilo: 与hilo类似, 只是主键历史状态保存在sequence中, 适用于支持sequence的数据库.
• increment: 主键按数值递增, 但如果多个实例同时访问同一个数据库, 各自生成主键,则容易造成主键重复.
• native: 由hibernate根据数据库适配器中的定义, 自动采用identity, hilo, sequence中的一种方式.
• foreign: 外部表的字段作主键.
• select: hibernate 3 中新增的.需要提供一个唯一的标识字段进行二次读取, 以获取触发器生成的主键值, 通过param子元素进行定义, 比如:

 

key_field

该方法主要针对遗留系统的改造工程, 一些早期的系统主键依赖于触发器生成. 当数据库insert时, 触发器捕获这一操作, 并为主键赋值, 在插入数据库后, 再次读取某一识别字段读取已经插入的数据, 获取其主键值.

5. OR映射---复合主键映射(composite-id)---实体属性组成主键

复合主键使用将取代id元素, 并具有property属性列表.

复合主键的POJO类需要实现equals和hashcode方法, 可以使用apache commons lang包中的工具类实现(commons-lang.jar), 比如:

 

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

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

import org.apache.commons.lang.builder.ToStringBuilder;

 

...

 

public String toString(){

return new ToStringBuilder(this)

.append("userid ", getUserid ())

.append("when", getWhen ())

.toString();

}

 

public boolean equals(Object other){

if(!(other instanceof MyPoJoClass)){

return false;

}

MyPoJoClass castOther=( MyPoJoClass)other;

return new EqualsBuilder()

.appendSuper(super.equals(other))

.append(this.getUserid (),castOther.getUserid() )

.append(this.getWhen (),castOther.getWhen() )

.isEquals();

}

 

public int hashCode(){

return new HashCodeBuilder()

.appendSuper(super.hashCode() )

.append(getUserid ())

.append(getWhen ())

.toHashCode();

}

装载复合主键的记录时, 考虑把类对应的对象的主键值填充好后作为load的第二个参数.

MyPoJoClass obj = new MyPoJoClass();

obj.setUserid(...);

obj.setWhen(...);

obj=(MyPoJoClass)session.load(MyPoJoClass.class, obj);

6. OR映射---复合主键映射(composite-id)---基于主键类

可以用一个独立的类来描述主键, 示例:

此时, 需要定义一个新的类KeyClass来作为主键类, KeyClass实现equals和hashcode方法, 而在POJO中, 使用属性名keyClassProperty来表示主键, 其类类型为KeyClass.

7. OR映射---composite-id其他子节点

composite-id除了key-property子节点外, 还具有可选子节点.完整的节点内容:

class="ClassName"

unsaved-value="any|none" >

 

name=" propertyName "

type="type_name" />

...

name=" propertyName " />

...

8. OR映射---属性/字段映射

name: POJO类的属性名,

type: POJO类中属性的数据类型; 如果是字符串,可以省略

column: 数据库中的字段名. 如果和属性同名, 可以省略.

9. OR映射---自定义数据类型 UserType, CompositeUserType接口

hibernate3 中的为: org.hibernate.usertype(hibernate2中为net.sf包)下面的两个接口: UserType 和 CompositeUserType . 它们提供自定义类型的规范, 这里以UserType为例.

package org.hibernate.usertype;

 

import java.io.Serializable;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

 

import org.hibernate.HibernateException;

 

public interface UserType {

 

/**

* 返回本类型所映射的SQL类型, 返回的是int[]数组. 可以取java.sql.Types中的int静态常量.

* 比如有: public final static int DOUBLE = 8;

*/

public int[] sqlTypes();

 

/**

* 定义本类型的nullSafeGet() 方法返回的数据的类型

*/

public Class returnedClass();

 

/**

* 定义两个数据的比较方法, 返回true表示相等, false表示不等.

*/

public boolean equals(Object x, Object y) throws HibernateException;

 

/**

* Get a hashcode for the instance, consistent with persistence "equality"

*/

public int hashCode(Object x) throws HibernateException;

 

/**

* 定义从ResultSet中读取数据并转换成自定义类型的方法, 对数据库null应该考虑

* 参数names 包含了当前自定义类型的映射字段名称

*/

public Object nullSafeGet(ResultSet rs, String[] names, Object owner)

throws HibernateException, SQLException;

 

/**

* Hibernate进行数据保存时被调用的方法

* @param st a JDBC prepared statement

* @param value the object to write, 类型应该是returnedClass()方法返回的Class指定的类型

* @param index statement parameter index

* @throws HibernateException

* @throws SQLException

*/

public void nullSafeSet(PreparedStatement st, Object value, int index)

throws HibernateException, SQLException;

/**

* 自定义的对象复制方法, 用作构造返回对象.

* nullSafeGet方法被调用后, Hibernate获得了自定义数据对象,

* 这个对象成为数据库读出的原始对象, 通过deepCopy方法, Hibernate

* 返回一个复本给用户. 脏数据检查时, 如果两个对象不等(equals方法返回false),

* 就会执行数据库持久化操作.

* @param value the object to be cloned, which may be null

* @return Object a copy

*/

public Object deepCopy(Object value) throws HibernateException;

 

/**

* Are objects of this type mutable?

* 本类型实例是否可变

* @return boolean

*/

public boolean isMutable();

 

/**

* 把对象转化为二级缓存中保存. 经常把当前对象对其他对象的引用, 保存为其id值.

* Transform the object into its cacheable representation. At the very least this

* method should perform a deep copy if the type is mutable. That may not be enough

* for some implementations, however; for example, associations must be cached as

* identifier values. (optional operation)

*

* @param value the object to be cached

* @return a cachable representation of the object

* @throws HibernateException

*/

public Serializable disassemble(Object value) throws HibernateException;

 

/**

* 把二级缓存中获取的数据转换为自定义的对象数据

* Reconstruct an object from the cacheable representation. At the very least this

* method should perform a deep copy if the type is mutable. (optional operation)

*

* @param cached the object to be cached

* @param owner the owner of the cached object

* @return a reconstructed object from the cachable representation

* @throws HibernateException

*/

public Object assemble(Serializable cached, Object owner) throws HibernateException;

 

/**

* During merge, replace the existing (target) value in the entity we are merging to

* with a new (original) value from the detached entity we are merging. For immutable

* objects, or null values, it is safe to simply return the first parameter. For

* mutable objects, it is safe to return a copy of the first parameter. For objects

* with component values, it might make sense to recursively replace component values.

*

* @param original the value from the detached entity being merged

* @param target the value in the managed entity

* @return the value to be merged

*/

public Object replace(Object original, Object target, Object owner)

throws HibernateException;

}

 

如果一个用户具有多个email, 可以分别定义多个字段保存, 也可以定义一个子表专门保存, 但都有点大动干戈. 可以考虑用一个字符串字段保存, 相邻的email用一个;隔开. 比如:

package cn.thinkmore.hibernate.pojo;

 

import java.io.Serializable;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.sql.Types;

import java.util.*;

 

import org.hibernate.Hibernate;

import org.hibernate.HibernateException;

import org.hibernate.usertype.UserType;

 

public class EmailList implements UserType {

 

private static final String SPLITTER = ";";

 

private static final int[] TYPES = new int[] { Types.VARCHAR };

 

public Object assemble(Serializable cached, Object owner)

throws HibernateException {

return null;

}

 

public Object deepCopy(Object value) throws HibernateException {

if (!(value instanceof List)) {

return null;

}

List src = (List) value;

List tar = new ArrayList();

tar.addAll(src);

return tar;

}

 

public Serializable disassemble(Object value) throws HibernateException {

return null;

}

 

public boolean equals(Object x, Object y) throws HibernateException {

if (x == y)

return true;

if (x != null && y != null) {

List xList = (List) x;

List yList = (List) y;

if (xList.size() != yList.size())

return false;

for (int i = 0; i < xList.size(); i++) {

String strX = xList.get(i).toString();

String strY = yList.get(i).toString();

if (!strX.equals(strY))

return false;

}

}

return false;

}

 

 

public boolean isMutable() {

return false;

}

 

public Object nullSafeGet(ResultSet rs, String[] names, Object owner)

throws HibernateException, SQLException {

String value = Hibernate.STRING.nullSafeGet(rs, names[0]).toString();

if(null!=value)

return parse(value);

return null;

}

 

private List parse(String value) {

String[] strs = org.apache.commons.lang.StringUtils.split(value,SPLITTER);

List emails = new ArrayList();

for(int i=0; i

emails.add(strs[i]);

}

return emails;

}

 

private String assemble(List list) {

StringBuilder sb = new StringBuilder();

int maxIndex = list.size()-1;

for(int i=0; i

sb.append(list.get(i)).append(SPLITTER);

}

if(0<=maxIndex){

sb.append(list.get(maxIndex));

}

return sb.toString();

}

 

public void nullSafeSet(PreparedStatement st, Object value, int index)

throws HibernateException, SQLException {

if(null!=value&&(value instanceof List)){

String str = assemble((List)value);

Hibernate.STRING.nullSafeSet(st,str,index);

}else if(null!=value){

Hibernate.STRING.nullSafeSet(st,value.toString(), index);

}else{

Hibernate.STRING.nullSafeSet(st,null, index);

}

}

 

public Object replace(Object original, Object target, Object owner)

throws HibernateException {

return null;

}

 

public Class returnedClass() {

return List.class;

}

 

public int[] sqlTypes() {

return TYPES;

}

 

public int hashCode(Object x) throws HibernateException {

return 0;

}

}

数据关联关系

数据关联关系在实体的子类里面不会被自动继承.

10. 一对一关联 ----- 主键关联 one-to-one

一对一的主键关联, 指两个表的记录是一对一的关系, 且一个表的主键取为另一个表对应的记录的主键.

name="gene" cascade="all" outer-join="true"

class="cn.thinkmore.hibernate.pojo.Gene" />

 

name: 属性名

class: java全路径类名

cascade: 是否级连操作, all , none

outer-join: 是否外链接, true/false

citizen

class="cn.thinkmore.hibernate.pojo.Citizen" />

 

Constrained: 次关联中的约束方.

.....

Session s = HibernateSession3.getSession();

Citizen one = new Citizen();

one.setIdcard("123456789012345678");

one.setName("Mike");

one.setSex("M");

Gene gene = new Gene();

gene.setBloodType("AB");

gene.setDna("Ajodjjd[[joa");

gene.setSpecial("White");

 

one.setGene(gene);

gene.setCitizen(one);

 

Transaction trans = s.beginTransaction();

s.saveOrUpdate(one);

trans.commit();

 

// 两条数据一起被保存, 查询时也会关联查出来.

Query query = s.createQuery("From Citizen");

List list = query.list();

for (int i = 0; i < list.size(); i++) {

one = (Citizen) list.get(i);

if (null == one)

continue;

gene = (Gene) one.getGene();

if (null != gene){

System.out.println(gene.getId()+":"+gene.getSpecial()+":"+gene.getDna());

}

}

11. 单向一对多关联 ----- 唯一外键关联 one-to-many

 

一个用户可以多个email:

 

 

12. 双向一对多关联

 

除了在主控方配置一对多, 还要在被控方配置对应的多对一关系:

 

User:

 

Email:

 

再有例子:一个职员(是人的子类)前后可能有多条工作(每次工作是一条记录):

Users may bid for or sell auction items.

 

cascade="all"

class="webapp.hibernate.pojo.Gene"/>

 

cascade="all"

class="webapp.hibernate.pojo.Gene"/>

 

 

public static void testOne2Many() {

Session s = HibernateSession3.getSession();

Employee e = new Employee();

e.setName("一对多");

e.setIdcard("123456789012345678");

e.setBirth(new java.sql.Date(System.currentTimeMillis()-24L*3600*1000*365*25));

 

JobList job1 = new JobList();

job1.setEmployee(e);

job1.setCompany("A gongsi");

job1.setBegin(new java.sql.Date(System.currentTimeMillis()-24L*3600*1000*365*5));

job1.setEnd(new java.sql.Date(System.currentTimeMillis()-24L*3600*1000*365*4));

 

JobList job2 = new JobList();

job2.setEmployee(e);

job2.setCompany("B gongsi");

job2.setBegin(new java.sql.Date(System.currentTimeMillis()-24L*3600*1000*365*4));

job2.setEnd(new java.sql.Date(System.currentTimeMillis()-24L*3600*1000*365*2));

 

Set jobs = new HashSet();

jobs.add(job1);

jobs.add(job2);

e.setJobs(jobs);

 

 

Transaction trans = s.beginTransaction();

// 两个表的数据一起被保存, 查询时也会关联查出来.

s.saveOrUpdate(e);

trans.commit();

 

 

Query query = s.createQuery("From Employee");

List list = query.list();

for (int i = 0; i < list.size(); i++) {

Employee one = (Employee) list.get(i);

if (null == one)

continue;

System.out.println(one.getName()+":"+one.getBirth()+":");

Set joblist = one.getJobs();

for(Object o:joblist){

JobList j = (JobList)o;

System.out.println("\t工作:"+j.getCompany()+":"+j.getBegin()+":"+j.getEnd());

}

System.out.println("---------------------------------------");

}

 

}

 

13. 双向多对多关联

一个用户可以在银行有多个帐号

User:

 

cascade="all"

class="webapp.hibernate.pojo.Gene"/>

 

Bank:

Users may bid for or sell auction items.

 

public static void testMany2Many() {

Session s = HibernateSession3.getSession();

Iterator itor =(Iterator)s.createQuery("FROM MoneyUser").iterate();

while(itor.hasNext()){

MoneyUser moneyUser = itor.next();

Set banks = moneyUser.getBanks();

Iterator bankItor = banks.iterator();

while(bankItor.hasNext()){

Bank bank = bankItor.next();

System.out.println(moneyUser.getName()+" "+bank.getBankname());

}

}

}

 

public static void testMany2Many2() {

Session s = HibernateSession3.getSession();

Iterator itor = s.createQuery("FROM Bank").iterate();

while(itor.hasNext()){

Bank bank = itor.next();

Set customers = bank.getCutomers();

Iterator customerItor = customers.iterator();

while(customerItor.hasNext()){

MoneyUser moneyUser = customerItor.next();

System.out.println(bank.getBankname()+" "+moneyUser.getName());

}

}

}