該想法來自群中
‘姠佑赱』 初始代碼由他提供
最初只能實(shí)現(xiàn)查詢，且效率較低
經(jīng)過one-to-one和one-to-many測試沒有問題，看直接復(fù)制到任何需要DAO的工程中使用
代碼
強(qiáng)烈建議在實(shí)際使用中加個接口
BaseDAO.JAVA
package com.lusm.HibernateSessionFactory;
import java.io.Serializable;
import java.util.List;
import org.hibernate.Query;
import org.hibernate.Session;
public class BaseDAO 
{
/** *//**
* 添加實(shí)體
* @param obj，要添加的實(shí)體對象
* @throws Exception
*/
public void add(Object obj) throws Exception{
Session session = null;
try {
session = HibernateSessionFactory.getSession();
session.save(obj);
session.beginTransaction().commit();
if(session!=null){
session.close();
}
} catch (RuntimeException e) {
session.beginTransaction().rollback();
if(session!=null){
session.close();
}
throw e;
}
}
/** *//**
* 刪除實(shí)體
* @param obj，要刪除的實(shí)體
* @throws Exception
*/
public void delete(Object obj) throws Exception{
Session session = null;
try {
//取得session對象
session =HibernateSessionFactory.getSession();
//刪除實(shí)體
session.delete(obj);
//提交事務(wù)
session.beginTransaction().commit();
if(session!=null){
session.close();
}
} catch (Exception e) {
session.beginTransaction().rollback();//事務(wù)回滾
if(session!=null){
session.close();
}
throw e;
}
}
/** *//**
* 更新實(shí)體
* @param obj，要更新的實(shí)體
* @throws Exception
*/
public void update(Object obj) throws Exception{
Session session=null;
try {
//取得session對象
session=HibernateSessionFactory.getSession();
//刪除實(shí)體
session.update(obj);
//提交事務(wù)
session.beginTransaction().commit();
if(session!=null){
session.close();
}
} catch (Exception e) {
session.beginTransaction().rollback();//事務(wù)回滾
if(session!=null){
session.close();
}
throw e;
}
}
/** *//**
* 根據(jù)指定的hql進(jìn)行查詢，并返回查詢結(jié)果
* @param hql，hql語句
* @return 查詢結(jié)果
* @throws Exception
*/
public List<?> findByHQL(String hql) throws Exception{
try {
Query queryObject =HibernateSessionFactory.getSession().createQuery(hql);
return queryObject.list();
} catch (Exception e) {
throw e;
}
}
/** *//**
* 根據(jù)指定的實(shí)體類型和主鍵的值，查找實(shí)體對象
* @param cls，實(shí)體的類
* @param key，主鍵的值
* @return，查找的實(shí)體對象
* @throws Exception
*/
public Object findById(String cls,Serializable key)
throws Exception
{
try {
Object instance = (Object) HibernateSessionFactory.getSession().get(cls, key);
return instance;
} catch (Exception e) {
throw e;
}
}
}
HibernateSessionFactory.java 我就不發(fā)了，每個工程里都有
值得注意到是：
寫代碼是必須考慮到效率，資源利用，第一，不要創(chuàng)建無謂的實(shí)例，第二，不要寫沒有必要的返回語句，第三，close是有目的的，不可以濫用，第四，必須考慮到哪一步出錯的概率高，必須在下一步先做判斷。
如下代碼就是很有問題的：
/** *//**
* 添加實(shí)體
* @param obj，要添加的實(shí)體對象
* @throws Exception
*/
public void add(Object obj) throws Exception{
Session ses=null;
Transaction tx=null;
try {
//取得session對象
ses=HibernateSessionFactory.getSession();
//開始事務(wù)
tx=ses.beginTransaction();
//保存實(shí)體
ses.save(obj);
//提交事務(wù)
tx.commit();
} catch (Exception e) {
tx.rollback();//事務(wù)回滾
throw e;
}finally{
//關(guān)閉session
HibernateSessionFactory.closeSession();
}
}
使用one-to-many中執(zhí)行刪除時， 你可能會遇到這樣的錯誤
Exception in thread "main" org.hibernate.TransientObjectException: the detached instance passed to delete() had a null identifier
.........
或者
Exception in thread "main" org.hibernate.TransientObjectException: the detached instance passed to delete() had a null identifier
at org.hibernate.event.def.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:63)
at org.hibernate.impl.SessionImpl.fireDelete(SessionImpl.java:761)
at org.hibernate.impl.SessionImpl.delete(SessionImpl.java:739)
at com.lusm.HibernateSessionFactory.BaseDAO.delete(BaseDAO.java:44)
at com.lusm.main.Del.main(Del.java:19)
或
Exception in thread "main" org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:71)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:202)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:235)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:144)
at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:297)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:985)
at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:333)
at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106)
at com.lusm.HibernateSessionFactory.BaseDAO.delete(BaseDAO.java:46)
at com.lusm.main.Del.main(Del.java:18)
Caused by: java.sql.BatchUpdateException: Cannot delete or update a parent row: a foreign key constraint fails (`lusm/test1`, CONSTRAINT `test1_ibfk_1` FOREIGN KEY (`id`) REFERENCES `test` (`id`))
at com.mysql.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:1669)
at com.mysql.jdbc.PreparedStatement.executeBatch(PreparedStatement.java:1085)
at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:58)
at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:195)
9 more
原因是你的xml配置和數(shù)據(jù)庫創(chuàng)建有問題
下面給出一個成功的例子
many
xml config
<?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">
<!--
Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
<class name="com.lusm.test.Test1" table="test1" catalog="lusm">
<id name="sid" type="java.lang.Integer">
<column name="sid" />
<generator class="increment" />
</id>
<many-to-one name="test" class="com.lusm.test.Test" fetch="select" cascade="save-update" >
<column name="id" not-null="true" />
</many-to-one>
<property name="sname" type="java.lang.String">
<column name="sname" length="20" />
</property>
</class>
</hibernate-mapping>
code
package com.lusm.test;
/** *//**
* Test1 generated by MyEclipse Persistence Tools
*/
public class Test1 implements java.io.Serializable {
// Fields
private Integer sid;
private Test test;
private String sname;
// Constructors
/** *//** default constructor */
public Test1() {
}
/** *//** minimal constructor */
public Test1(Test test) {
this.test = test;
}
/** *//** full constructor */
public Test1(Test test, String sname) {
this.test = test;
this.sname = sname;
}
// Property accessors
public Integer getSid() {
return this.sid;
}
public void setSid(Integer sid) {
this.sid = sid;
}
public Test getTest() {
return this.test;
}
public void setTest(Test test) {
this.test = test;
}
public String getSname() {
return this.sname;
}
public void setSname(String sname) {
this.sname = sname;
}
}
one
xml config
<?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">
<!--
Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
<class name="com.lusm.test.Test" table="test" catalog="lusm">
<id name="id" type="java.lang.Integer">
<column name="id" />
<generator class="increment" />
</id>
<property name="name" type="java.lang.String">
<column name="name" length="20" />
</property>
<set name="test1s" inverse="true">
<key>
<column name="id" not-null="true" />
</key>
<one-to-many class="com.lusm.test.Test1"/>
</set>
</class>
</hibernate-mapping>
code
package com.lusm.test;
import java.util.HashSet;
import java.util.Set;
/** *//**
* Test generated by MyEclipse Persistence Tools
*/
public class Test implements java.io.Serializable {
// Fields
private Integer id;
private String name;
private Set test1s = new HashSet(0);
// Constructors
/** *//** default constructor */
public Test() {
}
/** *//** full constructor */
public Test(String name, Set test1s) {
this.name = name;
this.test1s = test1s;
}
// Property accessors
public Integer getId() {
return this.id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
public Set getTest1s() {
return this.test1s;
}
public void setTest1s(Set test1s) {
this.test1s = test1s;
}
}
db sql
create table `lusm`.`test1`(
`sid` INT not null auto_increment,
`id` INT not null,
`sname` varchar(20),
primary key (`sid`),
index(sid),
foreign key(id) references test(id) ON DELETE CASCADE ON UPDATE CASCADE
);
create table `lusm`.`test`(
`id` INT not null auto_increment,
`name` VARCHAR(20),
primary key (`id`)
);
下面給出 該示例的兩個測試類
insert
package com.lusm.main;
import com.lusm.HibernateSessionFactory.BaseDAO;
import com.lusm.test.Test;
import com.lusm.test.Test1;
public class Main {
/** *//**
* @param args
* @throws Exception
*/
public static void main(String[] args) throws Exception {
Test test = new Test();
test.setName("nihao");
BaseDAO td = new BaseDAO();
td.add(test);
Test1 t1 = new Test1(test);
Test1 t2 = new Test1(test);
Test1 t3 = new Test1(test);
t1.setSid(1);
t2.setSid(2);
t3.setSid(3);
t1.setSname("nihao");
t2.setSname("mfafs");
t3.setSname("acncs");
BaseDAO td1 = new BaseDAO();
td1.add(t1);
td1.add(t2);
td1.add(t3);
}
}
delete
package com.lusm.main;
import com.lusm.HibernateSessionFactory.BaseDAO;
import com.lusm.test.Test;
public class Del {
/** *//**
* @param args
* @throws Exception
*/
public static void main(String[] args) throws Exception {
Test test = new Test();
test.setId(1);
BaseDAO bd = new BaseDAO();
bd.delete(test);
}
}
地震讓大伙知道：居安思危，才是生存之道。
posted on 2008-01-08 17:21
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