Vc调用ado访问数据库

Vc主要提供了两个类型来实现这一功能：
_ConnectionPtr m_Connection; //实现数据库的连接
_RecordsetPtr m_pRs; //访问记录集
访问数据库，主要包含以下几项功能：
1、 打开数据库连接
_bstr_t strCnn = strCon;
try
{
m_Connection.CreateInstance(__uuidof(Connection));
m_Connection->Open(strCnn,"","",NULL);
}catch(_com_error)
{
return;
}
_variant_t vDispatch((IDispatch*)m_Connection);
m_Connection->AddRef();

2、 向记录添加记录
CString strCmdText = "Select * from tblMapHeader";
try{
m_pRs1.CreateInstance(__uuidof(Recordset));
m_pRs1->CursorLocation = adUseClient;
m_pRs1->Open((LPCTSTR)strCmdText, vDispatch, adOpenKeyset,
adLockOptimistic, adCmdUnknown);
}catch(_com_error &e)
{

}
long rgIndices[1];
VARIANT rgf;
VARIANT rgv;
COleVariant fld[6], val[6];
SAFEARRAYBOUND bound;
int num = 6;
try
{
fld[0]="nFlag";
val[0].vt = VT_I8;
val[0].lVal =nFlag;

fld[1]="nScale";
val[1].vt = VT_I8;
val[1].lVal = nScale;

fld[2]="nTime";
val[2].vt = VT_I8;
val[2].lVal = nTime;

fld[3]="nProj";
val[3].vt = VT_I1;
val[3].intVal = nProj;

fld[4]="nReserved";
val[4].vt = VT_I1;
val[4].intVal = nReserved;

fld[5]="nHeight";
val[5].vt=VT_I8;
val[5].lVal = nHeight;

rgf.vt=VT_ARRAY|VT_VARIANT;
rgv.vt=VT_ARRAY|VT_VARIANT;

bound.cElements=num;
bound.lLbound=0;

rgv.parray=::SafeArrayCreate(VT_VARIANT,1,&bound);
if(rgv.parray==NULL)
AfxThrowMemoryException();
rgf.parray=::SafeArrayCreate(VT_VARIANT,1,&bound);
if(rgf.parray==NULL)
AfxThrowMemoryException();

for ( int i = 0; i < num; i++)
{
rgIndices[0]=i;
::SafeArrayPutElement(rgf.parray, rgIndices, &fld[i]);
::SafeArrayPutElement(rgv.parray, rgIndices, &val[i]);
}

m_pRs1->AddNew(&rgf,&rgv);
booChanged = true;
}
catch (_com_error &e)
{
AfxMessageBox(e.Description());
m_pRs1->CancelUpdate();
booChanged = false;
}
m_pRs1->Close();
注：也可写成下面的格式，只是sql数据变为insert即可。
3、 修改记录
strSql="Update tblGroundBaseInfo set TranType='' where GroundNo='"+m_strGroundNo+"'";
tmpRs.CreateInstance(__uuidof(Recordset));
tmpRs->CursorLocation = adUseClient;
tmpRs->Open((LPCTSTR)strSql,vDispatch,adOpenKeyset,adLockOptimistic,adCmdUnkown);
注：或写成m_pRs->Update(&rgf,&rgv);同添加记录相同
4、 删除记录
CString strIns;
strIns="delete from tmpStatByGround";
m_pRs.CreateInstance(__uuidof(Recordset));
m_pRs->CursorLocation = adUseClient;
m_pRs->Open((LPCTSTR)strIns, vDispatch, adOpenKeyset,
adLockOptimistic, adCmdUnknown);
5、 检索记录集
CString strCmdText = "Select * from tblMapHeader where szNum='"+sNum+"'";
_RecordsetPtr pRs;
try{
pRs.CreateInstance(__uuidof(Recordset));
pRs->CursorLocation = adUseClient;
pRs->Open((LPCTSTR)strCmdText, vDispatch,adOpenKeyset,
adLockOptimistic, adCmdText);
}catch(_com_error &e)
{

}
if(pRs->RecordCount > 0)
{
m_Header.nFlag = (long)pRs->Fields->GetItem("nFlag")->Value;
m_Header.nScale = (long)pRs->Fields->GetItem("nScale")->Value;
m_Header.nTime = (long)pRs->Fields->GetItem("nTime")->Value;
m_Header.nProj = (byte)pRs->Fields->GetItem("nProj")->Value;
m_Header.nReserved = (byte)pRs->Fields->GetItem("nReserved")->Value;
m_Header.nHeight = (long)pRs->Fields->GetItem("nHeight")->Value;
m_Header.ptOrg.x = (long)pRs->Fields->GetItem("ptOrgX")->Value;
m_Header.ptOrg.y = (long)pRs->Fields->GetItem("ptOrgY")->Value;
m_Header.fBaseLat = (double)pRs->Fields->GetItem("fBaseLat")->Value;
m_Header.left = (double)pRs->Fields->GetItem("left1")->Value;
m_Header.top = (double)pRs->Fields->GetItem("top1")->Value;
m_Header.right = (double)pRs->Fields->GetItem("right1")->Value;
m_Header.bottom = (double)pRs->Fields->GetItem("bottom1")->Value;

}
pRs->Close();
6、 关闭数据库连接
m_Connection.Release();
关于blob类型字段的使用
long lDataSize = pRecordRead->GetFields()->GetItem(pRec->sRecordName)->ActualSize;///得到数据的长度
_variant_t varBLOB;
varBLOB = pRecordRead->GetFields()->GetItem(pRec->sRecordName)->GetChunk(lDataSize);
pRecordWrite->GetFields()->GetItem(pRec->sRecordName)->AppendChunk(varBLOB);