spring + hibernate 设置更新指定字段
spring + hibernate 设置更新指定字段
hibernate的update方式默认的是更新所有字段的，这导致一个很大的问题，当想更新部分字段时必须要把整个entity先load一遍，然后set相应的更新字段再保存
这一步load数据势必将数据库的操作增加一倍，而且基本上是多余的，最近看了下hibernate源码，发现hibernate有设置指定更新的方式，具体方式如下

org.hibernate.persister.entity.AbstractEntityPersister中定义了基类的更新方法public void update(final Serializable id,        final Object[] fields,        final int[] dirtyFields,        final boolean hasDirtyCollection,        final Object[] oldFields,        final Object oldVersion,        final Object object,        final Object rowId,        final SessionImplementor session) throws HibernateException {

其中的一段代码：

if ( ( entityMetamodel.isDynamicUpdate() && dirtyFields != null ) ) {// We need to generate the UPDATE SQL when dynamic-update="true"propsToUpdate = getPropertiesToUpdate( dirtyFields, hasDirtyCollection );// don't need to check laziness (dirty checking algorithm handles that)updateStrings = new String[span];for ( int j = 0; j < span; j++ ) {updateStrings[j] = tableUpdateNeeded[j] ?generateUpdateString( propsToUpdate, j, oldFields, j == 0 && rowId != null ) :null;}}else if ( ! isModifiableEntity( entry ) ) {// We need to generate UPDATE SQL when a non-modifiable entity (e.g., read-only or immutable)// needs:// - to have references to transient entities set to null before being deleted// - to have version incremented do to a "dirty" association// If dirtyFields == null, then that means that there are no dirty properties to// to be updated; an empty array for the dirty fields needs to be passed to// getPropertiesToUpdate() instead of null.propsToUpdate = getPropertiesToUpdate(( dirtyFields == null ? ArrayHelper.EMPTY_INT_ARRAY : dirtyFields ),hasDirtyCollection);// don't need to check laziness (dirty checking algorithm handles that)updateStrings = new String[span];for ( int j = 0; j < span; j++ ) {updateStrings[j] = tableUpdateNeeded[j] ?generateUpdateString( propsToUpdate, j, oldFields, j == 0 && rowId != null ) :null;}}else {// For the case of dynamic-update="false", or no snapshot, we use the static SQLupdateStrings = getUpdateStrings(rowId != null,hasUninitializedLazyProperties( object ));propsToUpdate = getPropertyUpdateability( object );}

可以看到hibernate提供了3种的获得更新字段方式，默认情况下会进入最后的else中获得所有的字段，中间else if 的方式可以看到注解里的说明，应该是为read-only的对象准备，此处没有详细深入，而我们需要的是第一种方式
当对象的mapping文件配置了dynamic-update="true" 且dirtyFields存在时hibernate便会根据dirtyFields获得需要更新的字段
propsToUpdate = getPropertiesToUpdate( dirtyFields, hasDirtyCollection );
这里的dirtyFields便是entity对应的字段下标
一直向前追溯dirtyFields的来源可以在org.hibernate.event.internal.DefaultFlushEntityEventListener中找到protected void dirtyCheck(final FlushEntityEvent event) throws HibernateException函数
关键代码：

int[] dirtyProperties = session.getInterceptor().findDirty(entity,id,values,loadedState,persister.getPropertyNames(),persister.getPropertyTypes());

hibernate在session中做了一个拦截器，可以在操作前做一些处理。
session由sessionFactory创建，而interceptor则由从Configuration注入
这样就很清楚了，我们要做的操作只要在Configuration中注入我们自定义的interceptor就行了

先写一个interceptor继承与emtpyInterceptor

package net.esj.basic.dao.hibernate.sessioninterceptor;import java.io.Serializable;import java.util.HashSet;import java.util.Set;import net.esj.basic.pojo.AbstractPojo;import net.esj.basic.pojo.UpdateType;import net.esj.basic.pojo.Updater;import net.esj.basic.utils.JavaProtoTypeHelper;import org.hibernate.EmptyInterceptor;import org.hibernate.type.Type;import org.springframework.context.annotation.Scope;import org.springframework.stereotype.Component;@Component("dirtyFindInterceptor")@Scope("prototype")public class DirtyFindInterceptor extends EmptyInterceptor {@Overridepublic int[] findDirty(Object entity, Serializable id,Object[] currentState, Object[] previousState,String[] propertyNames, Type[] types) {if(entity instanceof AbstractPojo){Updater updater = ((AbstractPojo)entity).getUpdater();UpdateType type =((AbstractPojo)entity).getUpdateType();if(type==UpdateType.AUTO){type = checkUpdateType(entity, id, currentState, previousState, propertyNames, types);}switch(type){case BY_DIFF:return findDirtyByDiff(entity, id, currentState, previousState, propertyNames, types);case BY_UPDATER:return findDirtyByUpdater(entity, id, currentState, previousState, propertyNames, types, ((AbstractPojo)entity));case NONE:return super.findDirty(entity, id, currentState, previousState, propertyNames,types);}}return super.findDirty(entity, id, currentState, previousState, propertyNames,types);}protected UpdateType checkUpdateType(Object entity, Serializable id,Object[] currentState, Object[] previousState,String[] propertyNames, Type[] types){if(! (entity instanceof AbstractPojo)){return UpdateType.NONE;}Updater updater = ((AbstractPojo)entity).getUpdater();if(updater.hasProperty()){return UpdateType.BY_UPDATER;}return UpdateType.NONE;} private int[] findDirtyByUpdater(Object entity, Serializable id,Object[] currentState, Object[] previousState,String[] propertyNames, Type[] types,AbstractPojo pojo){Updater updater = pojo.getUpdater();Set<Integer> tmp = new HashSet<Integer>(); //int[] reval = new int[propertyNames.length];for(int i=0;i<propertyNames.length;i++){String propertyName = propertyNames[i];if(updater.getProperties().contains(propertyName)){tmp.add(i);}}int[] reval = new int[tmp.size()];int i=0;for(Integer t:tmp){reval[i] = t;i++;}return reval;}private int[] findDirtyByDiff(Object entity, Serializable id,Object[] currentState, Object[] previousState,String[] propertyNames, Type[] types){if(currentState==null|| previousState ==null){return null;}Set<Integer> tmp = new HashSet<Integer>(); for(int i=0;i<currentState.length;i++){Object cur = currentState[i];Object pre = previousState[i];if(!JavaProtoTypeHelper.equal(cur, pre)){tmp.add(i);}}int[] reval = new int[tmp.size()];int i=0;for(Integer t:tmp){reval[i] = t;i++;}return reval;}}

这里我做了3种更新方式，一种为基本的全字段更新，一种为根据程序员自定义的字段更新，一种为核查原始数据和新数据是否相等，更新不相等的字段。


基于spring的配置，我们的hibernate的Configuration是由LocalSessionFactoryBean创建的。
具体配置为：

<bean id="sessionFactory"/></property><property name="mappingDirectoryLocations"><list><value>classpath*:/net/esj/test/pojo/</value></list></property><property name="hibernateProperties"><props><prop key="hibernate.connection.release_mode">after_transaction</prop><prop key="hibernate.dialect">${hibernate.dialect}</prop>                <prop key="hibernate.show_sql">${hibernate.show_sql}</prop>                <prop key="hibernate.format_sql">${hibernate.format_sql}</prop></props></property><property name="entityInterceptor" ref="dirtyFindInterceptor" /></bean>

具体的过程可以在spring的源码中找到，此处我们注入上面的dirtyFindInterceptor类。


测试：

<hibernate-mapping package="net.esj.test.pojo"><classname="Foo"table="test_foo" dynamic-update="true"  //dynamic-update="true"此须增加><meta attribute="sync-DAO">true</meta><idname="id"type="string"column="id"><generator name="code">public void testUpdate(){Foo foo = new Foo();foo.setId("402881973aa11bb7013aa11bb8340000");foo.setName("asdas");foo.notifyUpdater("name");//只更新name字段baseDao.update(foo);}

hibernate打印的sql：
Hibernate: update test_foo set name=? where id=?
可以看到现在只更新了name字段