OAViewObject中clearCache(),reset(),setMaxFetchSize(-1)的使用

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今天在页面跳转之后，明明执行了查询，且查询语句正确的情况下，页面不显示数据，且点击SubmitButton包浏览器后退异常。

代码如下:

    OAViewObjectImpl vo=(OAViewObjectImpl)am.findViewObject("XXXVO1");
    vo.clearCache(); 
    vo.ExecuteQuery(headerid);
          
    public void ExecuteQuery(Number headerid)
    {
        clearCache();
        setWhereClauseParams(null);
        setWhereClauseParam(0, headerid);
        executeQuery();

    }

打印日志发现：
VO.getMaxFetchSize()==0;

VO.getFetchRowCount()==0;

所以页面不显示数据且触发POST数据时导致浏览器后退异常。

代码修改为如下即正常。

    OAViewObjectImpl vo=(OAViewObjectImpl)am.findViewObject("XXXVO1");
    vo.clearCache(); 
    vo.reset();
    vo.setMaxFetchSize(-1);
    vo.ExecuteQuery(headerid);
          
    public void ExecuteQuery(Number headerid)
    {
        clearCache();
        setWhereClauseParams(null);
        setWhereClauseParam(0, headerid);
        executeQuery();

    }

这使我对

    vo.clearCache(); 
    vo.reset();
    vo.setMaxFetchSize(-1);

Use the VO reset and clear cache both in the processFormRequest before redirecting to page again as well as in processRequest before initializing the VO.

But , Why???

这三个方法产生了强烈的兴趣。

查询JDev Doc得到以下结果：

关于clearCache()方法的官方文档介绍如下：

clearCache
public void clearCache()Clears the view object cache.
This method can be called for resource conservation. Calling this method also forces an automatic re-execution of the query for all RowSets, which refreshes the cache from the database.

Specified by:
clearCache in interface ViewObject
Overrides:
clearCache in class OAJboViewObjectImpl

关于reset()方法暂时未找到文档介绍。

关于setMaxFetchSize()的官方文档介绍如下：

setMaxFetchSize
public void setMaxFetchSize(int size)Maximum number of rows to fetch when a query is executed. This number takes effect the next time a query is executed.
Passing ‘-1‘ will retrieve all the rows. This is default behavior. (For OA Framework view objects, however, OA Framework initializes the maximum fetch size to be the value specified by "VO_MAX_FETCH_SIZE" profile option value.)

Passing ‘0‘ will result in the database query not being executed and also mark the view object as properly prepared for query execution.

Specified by:
setMaxFetchSize in interface ViewObject
Overrides:
setMaxFetchSize in class ViewObjectImpl
Parameters:
size - maximum number of rows to fetch
See Also:
executeQuery(), isPreparedForExecution(), setPreparedForExecution(boolean flag)

OAViewObject中clearCache(),reset(),setMaxFetchSize(-1)的使用

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原文地址：http://www.cnblogs.com/huanghongbo/p/5373307.html