如何实现ADO访问Blob类型

最新推荐文章于 2021-02-22 06:36:34 发布

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本文介绍了一个名为CDBMSSQL的类中两个关键方法：Load和Save的具体实现。Load方法用于从数据库加载指定ID的数据到缓冲区，而Save方法则将缓冲区中的数据保存到对应ID的数据库记录中。这两个方法通过使用_Recordset和_Connection对象来与数据库进行交互。

我把自己实际使用的代码贴出来供朋友参考

STDMETHODIMP CDBMSSQL::Load(long ID_Value, VARIANT *buf, short *pVal)
{
_RecordsetPtr mRecordset;
HRESULT hr;
_bstr_t mStrSQL;

hr = mRecordset.CreateInstance(__uuidof(Recordset));
if(FAILED(hr))
{
*pVal = -1;
return S_FALSE;
}

mStrSQL = " Select * From Users where ID =";
mStrSQL += (_bstr_t)ID_Value;

pConnection = NULL;
hr = pConnection.CreateInstance(__uuidof(Connection));

if(FAILED(hr))
{
*pVal = (short) -1;
return S_FALSE;
}

try
{
  pConnection->Open(this->mConnectionString,"","",NULL);
}
catch(_com_error &e)
{
  *pVal = (short) -2;
  return S_FALSE;
}

try
{
  pConnection->put_CursorLocation(adUseClient);
  mRecordset->Open(mStrSQL,
   pConnection.GetInterfacePtr(),
   adOpenDynamic,
   adLockOptimistic,
   adCmdText);
}
catch(_com_error &e)
{
  *pVal=(short)-3;
  return S_FALSE;
}

try
{
short irow=mRecordset->RecordCount;

  if (irow == 1)
  {
   long size = mRecordset->Fields->GetItem(this->mSample_Field)->ActualSize;
   if (size==0)
   {
    *pVal = (short) -5;
    return S_FALSE;
   }

   long i = 0;
   int lIsRead=0;
   _variant_t varChunk;
   unsigned char *buf1 = new unsigned char[size];
   long tmpsize = size;
   while(tmpsize>0)
   {
    lIsRead=tmpsize>=100? 100:tmpsize;
    varChunk = mRecordset->Fields->GetItem(this->mSample_Field)->GetChunk(lIsRead);
    for(long index=0;index<lIsRead;index++)
    {
     ::SafeArrayGetElement(varChunk.parray,&index,buf1+i*100+index);
    }

    tmpsize-=100;
    i++;
   }//while()

   SAFEARRAY *psa;
   SAFEARRAYBOUND rgsabound[1];
   rgsabound[0].cElements = size;
   rgsabound[0].lLbound = 0;
   psa = SafeArrayCreate(VT_UI1,1,rgsabound);

   for(i=0;i<size;i++)
   {
    SafeArrayPutElement(psa,&i,&(buf1[i]));
   }

   VARIANT data;
   data.vt = VT_ARRAY|VT_UI1;
   data.parray = psa;
   *buf = data;
   mRecordset->Close();

  }
  else
  {
   if(irow>1)
   {
    mRecordset->Close();
    *pVal = (short)-4;
    return S_FALSE;
   }
   else if(irow==0)
   {
    mRecordset->Close();
    *pVal =(short)-6;
    return S_FALSE;
   }
  }

}
catch(_com_error &e)
{
*pVal = (short) -99;
return S_FALSE;
}

*pVal = (short)0;
return S_OK;
}

STDMETHODIMP CDBMSSQL::Save(long ID_Value, VARIANT buf, short *pVal)
{
_RecordsetPtr mRecordset;
HRESULT hr;
_bstr_t mStrSQL;

hr = mRecordset.CreateInstance(__uuidof(Recordset));
if(FAILED(hr))
{
*pVal = (short) -1;
return S_FALSE;
}

mStrSQL = " Select * From Users where ID =";
mStrSQL += (_bstr_t)ID_Value;

pConnection = NULL;
hr = pConnection.CreateInstance(__uuidof(Connection));

if(FAILED(hr))
{
*pVal = (short) -1;
return S_FALSE;
}

try
{
  pConnection->Open(this->mConnectionString,"","",NULL);
}
catch(_com_error &e)
{
  *pVal = (short) -2;
  return S_FALSE;
}

try
{
  short irow=mRecordset->RecordCount;

  switch(irow)
  {
   case 0:
    mRecordset->AddNew();
    mRecordset->Fields->GetItem(this->mID_Field)->Value = ID_Value;
    mRecordset->Fields->GetItem(this->mSample_Field)->AppendChunk(buf);
    mRecordset->Update();
    mRecordset->Close();

    break;
   case 1:
    mRecordset->Fields->GetItem(this->mSample_Field)->AppendChunk(buf);

    mRecordset->Update();
    mRecordset->Close();
    break;
   default:
    *pVal = (short) -4;
    return S_FALSE;
    break;
  }

}
catch(_com_error &e)
{
*pVal = (short) -99;
return S_FALSE;
}
/**/
*pVal = (short)0;
return S_OK;
}