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标题:
在 C++Builder 中，如何自定义属性 [properties] ?
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作者:
韩冰
时间:
2005-1-26 12:32
标题:
在 C++Builder 中，如何自定义属性 [properties] ?
[摘自 水木清华站]
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对于SQL中的TEXT、IMAGE、MEMO字段的存取，可以采用下列程序：
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BLOB字段的读取：
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TBlobSTream* TemplateStream;
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char* TempPlatePtr;
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TemplateStream=new TBlobStream((TBlobField*)WebQuery->FieldByName
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("SearchTem"),bmReadWrite);
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TemplatePtr= new char[TemplateStream->Size];
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TemplateStream->Read(TemplatePtr, TemplateStream->Size);
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BLOB字段的写入：
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TBlobSTream* TemplateStream;
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char* TempPlatePtr;
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TemplateStream=new TBlobStream((TBlobField*)WebQuery->FieldByName
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("SearchTem"),bmReadWrite);
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TemplatePtr= new char[TemplateStream->Size];
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TemplateStream->Write(TemplatePtr, TemplateStream->Size);
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________________________________________________________________
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补充:
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获得字段的大小用函数datalength
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SQL Server端要作一点设置:
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By default, WRITETEXT is a nonlogged operation. This means that
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text or image data is not logged when it is written into the database.
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To use WRITETEXT in its default, nonlogged state,
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//注意!!
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the system administrator must use the sp_dboption system stored
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procedure to set select into/bulkcopy,
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//
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which allows nonlogged data to be inserted.
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做了试验,直接写SQL语句好象不行.
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____________________________________________________________________
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一些注意事项和一个例子
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在写入时:
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(1)如果使用的是TTable,则要将其ReadOnly属性先置为false,然后调用Edit函数;
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(2)如果使用的是TQuery,则要将其RequestLive属性先置为true,然后调用Edit函数;
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使得TTable(TQuery)是可写的.
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下面是一个使用TQuery往content表(主键file_id)中插入一条记录的例子,
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script为一个BLOB字段:
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TBlobStream *pScriptStream;
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//插入一条记录
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strSQL1="insert into content(file_id,script,key_image) values('";
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strSQL1=strSQL1+m_szFileID+"',null,null)";
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dmStoryEditor->qryExec->SQL->Clear();
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dmStoryEditor->qryExec->SQL->Add(strSQL1);
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dmStoryEditor->qryExec->ExecSQL();
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dmStoryEditor->qryExec->Close();
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//整理要写入的Blob数据
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LockMemories(NewsScript);
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NewsScript.GetEdition(NewsScript.m_ScriptHead.byteEditionNum);
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NewsScript.m_pScript=(BYTE *)GlobalLock(NewsScript.m_hScript);
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if(NewsScript.m_pScript!=NULL)
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{
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//再将刚插入的记录读出来,使该Query与该条记录关联
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strSQL1="select file_id,script from content where file_id='"+
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m_szFileID+"'";
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//允许该Query写
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dmStoryEditor->qryExec->RequestLive=true;
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dmStoryEditor->qryExec->SQL->Clear();
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dmStoryEditor->qryExec->SQL->Add(strSQL1);
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dmStoryEditor->qryExec->Open();
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dmStoryEditor->qryExec->First();
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//将该Query置为可写
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dmStoryEditor->qryExec->Edit();
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pScriptStream=new TBlobStream((TBlobField*)dmStoryEditor->
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qryExec->FieldByName("script"),bmReadWrite);
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pScriptStream->Write(NewsScript.m_pScript,
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NewsScript.m_lScriptRealSize);
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dmStoryEditor->qryExec->
ost();
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dmStoryEditor->qryExec->RequestLive=false;
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delete pScriptStream;
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}
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GlobalUnlock(NewsScript.m_hScript);
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UnLockMemories(NewsScript);
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