[问题] 一个ADO在C++里头的问题

[苦逼热狗]

第一次用ADO，有不少不懂得地方，希望大家帮忙
Q1:

HRESULT ExecuteSQL(const wchar_t* szUnicodeString)
{
HRESULT hr;
hr = recordset->Open(szUnicodeString,
connection.GetInterfacePtr(),
ADODB::adOpenForwardOnly,
ADODB::adLockReadOnly,
ADODB::adCmdText);
return hr;
}

wchar_t* pStatement;
pStatement = L"select * from userdata WHERE userid = 1";

if (ExecuteSQL(pStatement) == S_OK)
printf("select successuful\n");
else
printf("select failed\n");

我想知道能否在每次调用这个ExecuteSQL结束的时候
都清理一下recordset呢？
有啥函数可以调用呢

或者我需要每一次调用都生成一个instance,然后使用结束以后再摧毁掉

HRESULT ExecuteSQL(const wchar_t* szUnicodeString)
{
ADODB::_RecordsetPtr recordset;
HRESULT hr;
recordset.CreateInstance(__uuidof(ADODB::Recordset));
hr = recordset->Open(szUnicodeString,
					connection.GetInterfacePtr(), 
					ADODB::adOpenForwardOnly,
					ADODB::adLockReadOnly, 
					ADODB::adCmdText);

.........
//do something with the selected data from SQL
.........

recordset->Close();
recordset->Release();
recordset = NULL;
return hr;
}

ADO1.5 / VC++6.0

 

[dpff]

习惯上资源使用完后应该里立即释放，第二种做法是正确的。如果你的确需要将Recordset返回给调用者，最好Connection使用client游标，或者动态在内存创建一个跟原来结构一样的disconnected recordset，然后将需要的数据拷贝进去，然后释放原来的recordset。

 

[苦逼热狗]

我觉得我这么写会简单点，因为对ADO不熟悉

然后在只是简单update/insert一类的query时候，用之前第二种方法

HRESULT ExecuteSQL(const wchar_t* szUnicodeString, LPUSERDATA lpua)
{

ADODB::_RecordsetPtr recordset;
HRESULT hr;
_variant_t var;

RtlZeroMemory(lpua, sizeof(USERDATA));
recordset.CreateInstance(__uuidof(ADODB::Recordset));
hr = recordset->Open(szUnicodeString,
					connection.GetInterfacePtr(), 
					ADODB::adOpenForwardOnly,
					ADODB::adLockReadOnly, 
					ADODB::adCmdText);

var = recordset->Fields->GetItem(L"userid")->GetValue();
lpua->userid = var.intVal;
....
something like this
....


recordset->Close();
recordset->Release();
recordset = NULL;
return hr;
}

 

[dpff]

There is one place you may need to know that _RecordsetPtr is defined as something like _com_ptr<_Recordset>, which is actually a wrapper around ADO native interface using smart pointer, and its wrapper functions will throw exception in case of SQL error, and your "return hr" will never be executed.

 

[苦逼热狗]

okie, thanks for telling me that
i will use an additional try and catch to get the exception is anything goes wrong.