* save()方法提供了向数据库中添加数据的功能,但只能添加,这个DAO没有生成Update()的方法
* 但你可以简单的八save()方法改称具有Update功能:将getSession().save * (transientInstance);这句改成
* getSession().merge(transientInstance);或者getSession().saveOrUpdate
*  (transientInstance); 

public void save(User transientInstance) {
  log.debug("saving User instance");
  try {
   Session session=getSession();
   Transaction tx=session.beginTransaction();
   session.save(transientInstance);
   tx.commit();
   session.close();
   log.debug("save successful");
  } catch (RuntimeException re) {
   log.error("save failed", re);
   throw re;
  }
 }

delete()方法用来删除的 实际上我们会用下边的这个方法进行删除

public void delete(Integer id){
  log.debug("deleting User instance…");
  User user=findById(id);
  delete(user);
 }
 
 public void delete(User persistentInstance) {
  log.debug("deleting User instance");
  try {
   Session session=getSession();
   Transaction tx=session.beginTransaction();
   session.delete(persistentInstance);
   tx.commit();
   session.close();
   log.debug("delete successful");
  } catch (RuntimeException re) {
   log.error("delete failed", re);
   throw re;
  }
 }

根据编号进行查找

 public User findById(java.lang.Integer id) {
  log.debug("getting User instance with id: " + id);
  try {
   User instance = (User) getSession().get("hbm.User", id);
   return instance;
  } catch (RuntimeException re) {
   log.error("get failed", re);
   throw re;
  }
 }

findByExample()方法实现的功能相当于"select * from Usertable"实现的功能就是查询所有 数据.

 public List findByExample(User instance) {
  log.debug("finding User instance by example");
  try {
   List results = getSession().createCriteria("hbm.User").add(
     Example.create(instance)).list();
   log.debug("find by example successful, result size: "
     + results.size());
   return results;
  } catch (RuntimeException re) {
   log.error("find by example failed", re);
   throw re;
  }
 }

findByProperty()方法用来灵活的提供一种按条件查询的方法,你可以自己定义要按什么样的方 式查询.

 public List findByProperty(String propertyName, Object value) {
  log.debug("finding User instance with property: " + propertyName
    + ", value: " + value);
  try {
   String queryString = "from User as model where model."
     + propertyName + "= ?";
   Query queryObject = getSession().createQuery(queryString);
   queryObject.setParameter(0, value);
   return queryObject.list();
  } catch (RuntimeException re) {
   log.error("find by property name failed", re);
   throw re;
  }
 }

 public List findByName(Object name) {
  return findByProperty(NAME, name);
 }

 public List findBySex(Object sex) {
  return findByProperty(SEX, sex);
 }

 public List findByAge(Object age) {
  return findByProperty(AGE, age);
 }

 public List findAll() {
  log.debug("finding all User instances");
  try {
   String queryString = "from User";
   Query queryObject = getSession().createQuery(queryString);
   return queryObject.list();
  } catch (RuntimeException re) {
   log.error("find all failed", re);
   throw re;
  }
 }

将传入的detached状态的对象的属性复制到持久化对象中，并返回该持久化对象  如果该session中没有关联的持久化对象，加载一个，如果传入对象未保存，保存一个副本并作为持久对象返回，传入对象依然保持detached状态。 

可以用作更新数据

 public User merge(User detachedInstance) {
  log.debug("merging User instance");
  try {

    Session session=getSession();
   Transaction tx=session.beginTransaction();
   
   User result = (User) session.merge(detachedInstance);
   tx.commit();
   session.close();
   log.debug("merge successful");
   return result;
  } catch (RuntimeException re) {
   log.error("merge failed", re);
   throw re;
  }
 }

将传入的对象持久化并保存。 如果对象未保存（Transient状态），调用save方法保存。如果对象已保存（Detached状态），调用update方法将对象与Session重新关联。

 public void attachDirty(User instance) {
  log.debug("attaching dirty User instance");
  try {
   getSession().saveOrUpdate(instance);
   log.debug("attach successful");
  } catch (RuntimeException re) {
   log.error("attach failed", re);
   throw re;
  }
 }

将传入的对象状态设置为Transient状态 

 public void attachClean(User instance) {
  log.debug("attaching clean User instance");
  try {
   getSession().lock(instance, LockMode.NONE);
   log.debug("attach successful");
  } catch (RuntimeException re) {
   log.error("attach failed", re);
   throw re;
  }
 }