注意事项：
1.单向一对多
只需在“一”放进行配置
2.双向一对多
需要在关联双方都加以配置，而且需要在一的一方设置inverse=true
首先是实体类：
TAddress.java（多的一方）
public class TAddress implements Serializable { private static final long serialVersionUID = 1121137857691229229L; private Integer id; private String address; private String zipcode; private String tel; private String type; private TUser user; //必须有 ............} |
TUser.java（一的一方）
public class TUser implements Serializable { private static final long serialVersionUID = 1224691192698621789L; private Integer id; private Integer age; private String name; @SuppressWarnings("rawtypes") private Set address = new HashSet(); //多的一方放在集合中 |
....................} |
然后是各个实体类的配置文件
TAddress.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd" >
<!-- 一对多 -->
<hibernate-mapping>
<class name="com.model.TAddress" table="t_address"
dynamic-update="false" dynamic-insert="false">
<id name="id" type="java.lang.Integer" column="id" unsaved-value="0">
<generator class="native" />
</id>
<property name="address" column="address" type="string" />
<property name="tel" column="tel" type="string" />
<property name="zipcode" column="zipcode" type="string" />
<property name="type" column="type" type="string" />
<!-- 必须有many-to-one 否则关联字段（user_id）为null -->
<many-to-one name="user"
class="com.model.TUser"
cascade="none"
outer-join="auto"
update="true"
insert="true"
access="property"
column="user_id"
not-null="true">
</many-to-one>
</class>
</hibernate-mapping>
TUser.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd" >
<!-- 一对多 外键关联 -->
<!-- Select from TUser where id=1 Select from TUser where id=1 to Select
from TUser where id=1 or id=2 -->
<!-- batch-size 批量加载机制 可以自定义每次批量加载的数量 -->
<hibernate-mapping>
<class name="com.model.TUser" table="t_user" dynamic-update="true"
>
<id name="id" type="java.lang.Integer" column="id" unsaved-value="0">
<generator class="native" />
</id>
<property name="name" column="name" />
<property name="age" column="age" />
<set name="address" table="t_address" cascade="all" order-by="zipcode asc"
lazy="true" inverse="true">
<key column="user_id" /><!-- 确定关联的外键列 -->
<one-to-many class="com.model.TAddress" />
</set>
</class>
</hibernate-mapping>
其次是hibernate.cfg.xml
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-2.0.dtd">
<hibernate-configuration>
<session-factory>
<!-- properties -->
<!-- 数据库URL -->
<property name="hibernate.connection.url">jdbc:mysql://localhost/onetomany</property>
<!-- 数据库JDBC驱动 -->
<property name="hibernate.connection.driver_class">org.gjt.mm.mysql.Driver</property>
<!-- 数据库用户名 -->
<property name="hibernate.connection.username">S2223</property>
<!-- 数据库密码 -->
<property name="hibernate.connection.password">S2223</property>
<!-- 数据库方言 -->
<property name="dialect">net.sf.hibernate.dialect.MySQLDialect</property>
<!-- 是否日志调试 -->
<property name="show_sql">true</property>
<!-- 是否使用数据库外连接 -->
<property name="use_outer_join">true</property>
<!-- 事务管理 使用JDBC Transaction（使用JTA会报错） -->
<property name="transaction.factory_class">
net.sf.hibernate.transaction.JDBCTransactionFactory
</property>
<!-- 指定hibernate每次提交的SQL数量 对批量操作的性能提升帮助很大！！！ -->
<property name="hibernate.jdbc.batch_size">25</property>
<!-- 映射文件配置，配置文件名必须包含其相对于根的全路径 -->
<mapping resource="cn/happy/entity/TUser.hbm.xml" />
<mapping resource="cn/happy/entityTAddress.hbm.xml" />
</session-factory>
</hibernate-configuration>
测试代码（部分）
增加
public void testSave(){ try { Transaction tx=session.beginTransaction(); // TUser user=(TUser) session.load(TUser.class, 1); TUser user=new TUser(); user.setName("zhangsan"); user.setAge(20); TAddress address=new TAddress(); address.setAddress("jingsan"); address.setTel("1361380"); address.setZipcode("45000"); address.setType("java"); address.setUser(user); //设置关联的TUser对象 user.getAddress().add(address); session.save(user); //级联更新 tx.commit(); } catch (HibernateException e) { e.printStackTrace(); } } |
查询
public void testLoad(){ try { Transaction tx=session.beginTransaction(); String hql="from TUser where name='zhangsan'"; List list=session.createQuery(hql).list(); System.out.println("-------------1------------"); Iterator iter=list.iterator(); while(iter.hasNext()){ TUser user=(TUser) iter.next(); System.out.println("--------------2------------"); System.out.println("user.name="+user.getName()); System.out.println("--------------3------------"); System.out.println("user.address="+user.getAddress().size()); System.out.println("--------------4------------"); } } catch (HibernateException e) { e.printStackTrace(); } } |
批量插入（可以提高性能）
实现机制：如果使用了批量加载机制，hibernate在进行数据查询操作前，会自动在当前session中寻找是否还存在
其他同类型待加载的数据，如果有，则将其查询条件合并在当前的select语句中一并提交，这样，通过
一次数据库操作即完成了多个读取任务。
//批量插入操作性能优化 通过配置<property name="hibernate.jdbc.batch_size">25</property> public void testBatchInsert(){ long start=System.currentTimeMillis(); this.importUserList(); long end=System.currentTimeMillis(); System.out.println("批量插入花费时间是"+(end-start)); } public void importUserList(){ try { Transaction tx=session.beginTransaction(); for(int i=0;i<10000;i++){ TUser user=new TUser(); user.setName("user"+i); session.save(user); if(i%25==0){ //以每25个数据作为一个处理单元 session.flush(); session.clear(); } } tx.commit(); } catch (HibernateException e) { e.printStackTrace(); } } |