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:

<?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">

<hibernate-mapping>

  <class name="cn.thinkmore.hibernate.pojo.Tuser" table="T_user">

     <id column="id" name="id"  type="java.lang.Integer">

         <generator class="increment" />

     </id>

     <property column="name" name="name" type="java.lang.String"/>

  </class>

</hibernate-mapping>

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

<class name="cn.thinkmore.hibernate.pojo.Tuser" table="T_user">

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

<id name="id" type="java.lang.Integer" column="id">

     <generator class="increment" />

</id>

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:

<generator class="select">

    <param name="key">key_field</param>

</generator>

   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<composite-id>将取代id元素, 并具有property属性列表.

<composite-id>

      <key-property column="userid" name="userid" type="java.lang.String" />

      <key-property column="when" name="when" type="java.sql.Date" />

    </composite-id>

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:

<composite-id name="keyClassProperty" class="MyPoJoClass">

      <key-property column="userid" name="userid" type="java.lang.String" />

      <key-property column="when" name="when" type="java.sql.Date" />

    </composite-id>

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<key-many-to-one>子节点.完整的节点内容:

<composite-id name="propertyName"

class="ClassName"

unsaved-value="any|none" >

 

      <key-property column="colum_name"

name=" propertyName "

type="type_name" />

...

      <key-many-to-one  column=" colum_name " calss=" ClassName "

  name=" propertyName " />

...

    </composite-id>

8.   OR映射---属性/字段映射

<property name="name" type="java.lang.String" column="name" />

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<String> emails = new ArrayList<String>();

            for(int i=0; i<strs.length;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<maxIndex;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.

<hibernate-mapping>

    <class name="cn.thinkmore.hibernate.pojo.Citizen" table="citizen" lazy="true">

       <id name="id" column="id">     

           <generator class="uuid.hex" />

       </id>

       <property name="name" />

       <property name="sex"/>

       <property name="idcard" />

       <property name="address"/>

        <one-to-one name="gene"  cascade="all"  outer-join="true"

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

    </class>

</hibernate-mapping>

 

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

<hibernate-mapping>

    <class name="cn.thinkmore.hibernate.pojo.Gene" table="gene" lazy="true">

       <id name="id" column="id" >    

           <generator class="foreign">

             <param name="property">citizen</param>

           </generator>

       </id>

       <property name="dna" />

       <property name="chromosome"/>

       <property name="species"/>

       <one-to-one name="citizen"  constrained="true"

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

    </class>

</hibernate-mapping>

 

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:

 

<set name="email" table="emails" cascade="all">

    <key column="userid" />

<one-to-many calss="....Email" />

</set>

 

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:

<set name="email" table="emails" cascade="all" inverse="true">

    <key column="userid" />

<one-to-many calss="....Email" />

</set>

 

Email:

<many-to-one  name="user" class=".....User" cascade="none" column="userid" />

 

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):

<hibernate-mapping >

    <class name="webapp.hibernate.pojo.People" table="people" lazy="false">

       <comment>Users may bid for or sell auction items.</comment>

       <id name="id">    

           <generator class="uuid.hex"/>

       </id> 

       <property name="name" />

       <property name="idcard" /> 

       <property name="sex"/>            

       <property name="birth" type="date"/>

      

        <one-to-one name="gene"

                    cascade="all"

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

    </class>  

</hibernate-mapping>

 

<hibernate-mapping >

    <class name="webapp.hibernate.pojo.Employee" table="people" lazy="false">

       <id name="id">    

           <generator class="uuid.hex"/>

       </id> 

       <property name="name" />

       <property name="idcard" /> 

       <property name="sex"/>            

       <property name="birth" type="date"/>

       <one-to-one name="gene"

                    cascade="all"

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

                    

       <set name="jobs" table="joblist" cascade="all" inverse="true">

            <key column="empid" />

            <one-to-many class="webapp.hibernate.pojo.JobList" />  

       </set>                 

    </class>  

</hibernate-mapping>

 

<hibernate-mapping >

    <class name="webapp.hibernate.pojo.JobList" table="joblist" lazy="false">

       <id name="id">    

           <generator class="uuid.hex"/>

       </id> 

<!--       <property name="userid" column="empid"/> --> 

       <property name="company" />

       <property name="begin" type="date"/>            

       <property name="end" type="date"/>

       <many-to-one  name="employee" class="webapp.hibernate.pojo.Employee" cascade="none" column="empid" />       

    </class>  

</hibernate-mapping>

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<JobList> jobs = new HashSet<JobList>();

       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:

    <class name="webapp.hibernate.pojo.MoneyUser" table="people" lazy="false">

       <id name="id">     

           <generator class="uuid.hex"/>

       </id> 

       <property name="name" />

       <property name="idcard" /> 

       <property name="sex"/>            

       <property name="birth" type="date"/>

      

        <one-to-one name="gene"

                    cascade="all"

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

         <set name="banks" table="bankuser" cascade="none" >

            <key column="userid" />

            <many-to-many class="webapp.hibernate.pojo.Bank" column="bankid" /> 

         </set>

    </class>  

 

Bank:

<class name="webapp.hibernate.pojo.Bank" table="bank" lazy="false">

       <comment>Users may bid for or sell auction items.</comment>

       <id name="id">    

           <generator class="uuid.hex"/>

       </id> 

       <property name="bankname" />   

       <property name="type"/>           

       <property name="createday" type="date"/>

        <set name="cutomers" table="bankuser" cascade="none" >

            <key column="bankid" />

            <many-to-many class="webapp.hibernate.pojo.MoneyUser" column="userid" /> 

         </set>

    </class>  

    public static void testMany2Many() {

       Session s = HibernateSession3.getSession();

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

       while(itor.hasNext()){

           MoneyUser moneyUser =  itor.next();

           Set banks = moneyUser.getBanks();

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

       while(itor.hasNext()){

           Bank bank =  itor.next();

           Set customers = bank.getCutomers();

           Iterator<MoneyUser> customerItor = customers.iterator();

           while(customerItor.hasNext()){

              MoneyUser moneyUser = customerItor.next();

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

           }

       }

    }

 

原文地址:https://www.cnblogs.com/linzheng/p/1924852.html