VC調用SQLServer存儲過程的通用方法,只需要普通的查詢就可以實現。
這裡討論的是ADO調用存儲過程,按MSDN的例子,一般都是下面的調用方法(節選自MSDN):
HRESULT hr = S_OK;
// Define ADO object pointers.
// Initialize pointers on define.
// These are in the ADODB:: namespace.
_RecordsetPtr pRstByRoyalty = NULL;
_RecordsetPtr pRstAuthors = NULL;
_CommandPtr pcmdByRoyalty = NULL;
_ParameterPtr pprmByRoyalty = NULL;
_ConnectionPtr pConnection = NULL;
_bstr_t strCnn("Provider=sqloledb;Data Source=srv;"
"Initial Catalog=Pubs;User Id=sa;PassWord=;");
_bstr_t strMessage, strAuthorID;
int intRoyalty;
VARIANT vtRoyalty;
try
{
//Open a Connection.
TESTHR(pConnection.CreateInstance(__uuidof(Connection)));
hr = pConnection->Open(strCnn,"","",NULL);
pConnection->CursorLocation = adUseClIEnt;
//Open Command Object with one Parameter
TESTHR(pcmdByRoyalty.CreateInstance(__uuidof(Command)));
pcmdByRoyalty->CommandText = "byroyalty";
pcmdByRoyalty->CommandType = adCmdStoredProc;
//Define Integer/variant.
vtRoyalty.vt = VT_I2;
vtRoyalty.iVal = intRoyalty;
pprmByRoyalty = pcmdByRoyalty->CreateParameter(
"percentage",adInteger,adParamInput,sizeof(int),vtRoyalty);
pcmdByRoyalty->Parameters->Append(pprmByRoyalty);
pprmByRoyalty->Value = vtRoyalty;
//Create Recordset by executing the command
pcmdByRoyalty->ActiveConnection = pConnection;
pRstByRoyalty = pcmdByRoyalty->Execute(
NULL,NULL,adCmdStoredProc);
//執行結果的處理,省略...
pRstByRoyalty->Close();
pRstAuthors->Close();
pConnection->Close();
}
catch(_com_error &e)
{
//意外處理...
}
必須指定執行SQL語句的CommandType是adCmdStoredProc,存儲過程有參數就必須CreateParameter生成參數,這樣調用存儲過程就成了很麻煩的一件事情,必須針對不同的存儲過程生成不同的參數。一個兩個還可以接受,如果項目的業務邏輯比較復雜,需要依賴大量的存儲過程,並且項目的需求或功能可能要經常變動或擴展,那就成了一個噩夢了。有沒有通用的方法呢?當然有,只需要通用的查詢就可以實現。
_ConnectionPtr pConnection = NULL;
m_Conn.CreateInstance(__uuidof(Connection));
m_Conn->ConnectionString = "Provider=sqloledb;Data Source=srv;"Initial Catalog=Pubs;User Id=sa;PassWord=;";
m_Conn->Open("","","",NULL);
_variant_t m_param;
_bstr_t m_bstr;
int index = 0,nFIEldCount;
_RecordsetPtr m_Rs;
m_Rs.CreateInstance(__uuidof(Recordset));
m_Rs->Open("select * from titles",(IDispatch*)(m_Conn->m_Conn),adOpenStatic, adLockReadOnly,adCmdText);
nFieldCount = m_Rs->FIElds->Count;
while(!m_Rs->EndOfFile)
for(index=0;index < nFIEldCount;index ++)
{
m_param.Clear();
m_param = (short)index;
m_param = m_Rs->FIElds->GetItem(m_param);
if(m_param.vt != VT_NULL)
m_bstr = m_param;
else
m_bstr = "";
printf("%s\n",(char*)m_bstr);
}
m_Rs->MoveNext();
m_Rs->Close();
m_Conn->Close();
以上一段就是普通的執行查詢SQL語句的代碼,簡單起見,去掉了所有防護和判斷代碼,對於MS SQLServer,如果是執行返回結果集的存儲過程,比如Pubs的byroyalty,只需要把上面代碼中的"select * from titles"替換成"byroyalty 100"就可以了,即"過程名 參數1,參數2,..."形式。
這樣一來,不需要生成參數,只需要改變SQL語句,就實現了MS SQLServer存儲過程的調用,可以通用。但是對於返回參數的存儲過程,這段代碼就不行了,不過還是可以通過SQL語句解決:
“declare @q int exec checkpwd 'user','pwd',@ret = @q OUTPUT select @q”
checkpwd是一個存儲過程,兩個輸入參數,用戶名和密碼,第三個是輸出參數@ret,返回用戶驗證的結果。通過執行上面的SQL語句,把輸出參數作為結果集返回,就可以適應上面的VC代碼了。返回值的存儲過程也是一樣,執行“declare @q int,@return int exec @return = checkpwd 'user','pwd',@ret = @q OUTPUT select @q,@return”就可以了。
這裡講的是SQLServer的存儲過程調用,這段代碼同樣可以調用Oracle的存儲過程,不過需要對SQL語句作出一些調整,留待下一篇再說了。