JDO使用总结

相关demo项目查看

http://acheron.iteye.com/admin/blogs/402499

 

常见操作

 

A.查询操作

	public List<Record> listAllRecord() {
		PersistenceManager pm = getPersistenceManager();
//		Transaction tx= pm.currentTransaction();
		try {
//			tx.begin();
			Query query = pm.newQuery(Record.class);
			query.setOrdering("addDate DESC");

//方法1:获得查询结果,得到对象数组
//			Collection entries = (Collection) query.execute();
//			Object objRecord[]=(Object [])entries.toArray();
			
//方式2:枚举集合中的entity并作单独处理			
//			Collection entries = (Collection) query.execute();
//			Iterator i = entries.iterator();
//			while (i.hasNext()) {
//				Record obj = (Record) i.next();
//				System.out.println("do sth on the record!");
//			}

//方法3:获得list,显式把返回的Collection对象转换为List对象			
//			Collection entries = (Collection) query.execute();
//			List<Record> list = new ArrayList(entries);			
			
//方法4:直接强制转换为List返回
			List<Record> list = (List<Record>) query.execute();
			
//			tx.commit(); 
			return list;
		} catch (Exception e) {
			e.printStackTrace();
//			if (tx.isActive()) {
//				tx.rollback();
//			}
		}
	
query.execute();
		return null;
	}
	
	public List<Record> listAllRecord(int page) {
		PersistenceManager pm = getPersistenceManager();
//		Transaction tx= pm.currentTransaction();;
		try {
			page = (page == 0) ? 1 : page;
			Query query = pm.newQuery(Record.class);
			query.setOrdering("addDate DESC");
			query.setRange(PAGE_SIZE * (page - 1), PAGE_SIZE * page);
			return (List<Record>) pm.detachCopyAll((Collection<Record>) query.execute());
		} finally {
			releasePersistenceManager(pm);
		}
	}
	
	public int getPage(){
		PersistenceManager pm = getPersistenceManager();
		Query query = pm.newQuery(Record.class);
		query.setOrdering("addDate DESC");
		List<Record> list = (List<Record>) query.execute();
		return (int)(list.size()/10+1);
	}

 

 

B.删除操作

	public void removeRecordById(Long id) {
		PersistenceManager pm = getPersistenceManager();
//		Transaction tx= pm.currentTransaction();
		try {
//			tx.begin();
			Extent r = pm.getExtent (Record.class, false);
			String filter = "id == "+id;//注意是==
			Query query = pm.newQuery(r,filter);

//方式1:迭代Collection获得元素然后处理
//			Collection entries = (Collection) query.execute();
//			Iterator i = entries.iterator();
//			while (i.hasNext()) {
//				Record delRecord = (Record) i.next();
//				pm.deletePersistent(delRecord);
//			}		

//方式2:作为list处理
			List<Record> list = (List<Record>) query.execute();
//			if(!list.isEmpty()){}//isEmpty是首先判断是否为空（null）,然后判断size
//			if(list.size()!=0){ }
//			if(list.iterator().hasNext()){}
			if(!list.isEmpty()){
				Record delRecord = list.get(0);
				pm.deletePersistent(delRecord);
			}
			
//			tx.commit();
		}catch (Exception e) {
			e.printStackTrace();
//			if (tx.isActive()) {
//				tx.rollback();
//			}
		}
	}

 

异常处理:

dataNucleus Enhancer (version 1.1.0) : Enhancement of classes

2009-6-1 16:02:25 org.datanucleus.metadata.MetaDataManager loadClasses
严重: Class "com.jun.demos.book.dao.RecordJdoDao" was not found in the CLASSPATH. Please check your specification and your CLASSPATH.
org.datanucleus.exceptions.ClassNotResolvedException: Class "com.jun.demos.book.dao.RecordJdoDao" was not found in the CLASSPATH. Please check your specification and your CLASSPATH.
	at org.datanucleus.JDOClassLoaderResolver.classForName(JDOClassLoaderResolver.java:255)
	at org.datanucleus.JDOClassLoaderResolver.classForName(JDOClassLoaderResolver.java:420)
	at org.datanucleus.metadata.MetaDataManager.loadClasses(MetaDataManager.java:337)
	at org.datanucleus.enhancer.DataNucleusEnhancer.getFileMetadataForInput(DataNucleusEnhancer.java:723)
	at org.datanucleus.enhancer.DataNucleusEnhancer.enhance(DataNucleusEnhancer.java:525)
	at org.datanucleus.enhancer.DataNucleusEnhancer.main(DataNucleusEnhancer.java:1235)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at com.google.appengine.tools.enhancer.Enhancer.execute(Enhancer.java:57)
	at com.google.appengine.tools.enhancer.Enhance.<init>(Enhance.java:60)
	at com.google.appengine.tools.enhancer.Enhance.main(Enhance.java:41)

DataNucleus Enhancer completed with success for 0 classes. Timings : input=78 ms, enhance=0 ms, total=78 ms. Consult the log for full details
DataNucleus Enhancer completed and no classes were enhanced. Consult the log for full details

 

解决方法：

这个错误是因为spring的JdoSupport依赖于spring-dao.jar ，

也就是需要spring-jdo.jar和spring-dao.jar加到构建目录中。