Update- und CancelUpdate-Methode – Beispiel (VC++)
In diesem Beispiel wird die Verwendung der Update-Methode in Verbindung mit der CancelUpdate-Methode veranschaulicht.
// Update_CancelUpdate_Methods_Sample.cpp
// compile with: /EHsc /c
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")
#include <stdio.h>
#include <ole2.h>
#include <malloc.h>
#include <conio.h>
#include "icrsint.h"
//This Class extracts only fname,lname from employee table.
class CEmployeeRs : public CADORecordBinding {
BEGIN_ADO_BINDING(CEmployeeRs)
// fname is the 1st field in the recordset
ADO_VARIABLE_LENGTH_ENTRY2(1, adVarChar, m_sze_fname,
sizeof(m_sze_fname), le_fnameStatus, FALSE)
// lname is the 2nd field in the recordset.
ADO_VARIABLE_LENGTH_ENTRY2(2, adVarChar, m_sze_lname,
sizeof(m_sze_lname), le_lnameStatus, FALSE)
END_ADO_BINDING()
public:
CHAR m_sze_lname[31];
ULONG le_lnameStatus;
CHAR m_sze_fname[21];
ULONG le_fnameStatus;
};
// This Class extracts only empid,fname,lname,from employee table.
class CEmployeeRs1 : public CADORecordBinding {
BEGIN_ADO_BINDING(CEmployeeRs1)
// emp_id is the 1st field in the table.
ADO_VARIABLE_LENGTH_ENTRY2(1, adVarChar, m_sze_empid,
sizeof(m_sze_empid), le_empidStatus, FALSE)
// fname is the 2nd field in the table.
ADO_VARIABLE_LENGTH_ENTRY2(2, adVarChar, m_sze_fname,
sizeof(m_sze_fname), le_fnameStatus, FALSE)
// lname is the 4rt field in the table.
ADO_VARIABLE_LENGTH_ENTRY2(4, adVarChar, m_sze_lname,
sizeof(m_sze_lname), le_lnameStatus, FALSE)
END_ADO_BINDING()
public:
CHAR m_sze_empid[10];
ULONG le_empidStatus;
CHAR m_sze_lname[31];
ULONG le_lnameStatus;
CHAR m_sze_fname[21];
ULONG le_fnameStatus;
};
// Function Declartion.
inline void TESTHR(HRESULT x) { if FAILED(x) _com_issue_error(x); };
void UpdateX();
void UpdateX2();
void PrintProviderError(_ConnectionPtr pConnection);
void PrintComError(_com_error &e);
int main() {
if ( FAILED(::CoInitialize(NULL)) )
return -1;
UpdateX();
UpdateX2();
::CoUninitialize();
}
void UpdateX() {
// Define ADO object pointers. // Initialize pointers on define.
// These are in the ADODB:: namespace.
_RecordsetPtr pRstEmployees = NULL;
// Define string variables.
_bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");
IADORecordBinding *picRs = NULL; // Interface Pointer declared
CEmployeeRs emprs; // C++ Class object.
try {
// Open recordset with names from Employee table.
TESTHR(pRstEmployees.CreateInstance(__uuidof(Recordset)));
pRstEmployees->CursorType = adOpenKeyset;
pRstEmployees->LockType = adLockOptimistic;
pRstEmployees->Open("SELECT fname, lname FROM Employee "
"ORDER BY lname",strCnn,adOpenKeyset,adLockOptimistic, adCmdText);
// Store original data.
_bstr_t strOldFirst = pRstEmployees->Fields->GetItem("fname")->Value;
_bstr_t strOldLast = pRstEmployees->Fields->GetItem("lname")->Value;
// Change data in edit buffer.
pRstEmployees->Fields->GetItem("fname")->Value = (_bstr_t)("Linda");
pRstEmployees->Fields->GetItem("lname")->Value = (_bstr_t)("Kobara");
// Show contents of buffer and get user input.
printf("\n\nEdit in progress:\n\n");
printf("Original data = %s %s \n", (LPSTR)strOldFirst, (LPSTR)strOldLast);
printf("Data in buffer = %s %s",
(LPSTR)(_bstr_t) pRstEmployees->Fields->GetItem("fname")->Value,\
(LPSTR) (_bstr_t) pRstEmployees->Fields->GetItem("lname")->Value);
// Ask if the User wants to Update
printf("\n\nUse Update to replace the original data with the"
" buffered data in the Recordset? (y/n): ");
int chKey = _getch();
if ( toupper(chKey) == 'Y' )
pRstEmployees->Update();
else
pRstEmployees->CancelUpdate();
// Open an IADORecordBinding interface pointer for binding Recordset to a class.
TESTHR(pRstEmployees->QueryInterface(__uuidof(IADORecordBinding), (LPVOID*)&picRs));
// Bind the Recordset to a C++ Class here.
TESTHR(picRs->BindToRecordset(&emprs));
pRstEmployees->MoveFirst();
// Show the resulting data.
printf("\nData in recordset = %s %s", emprs.le_fnameStatus ==
adFldOK ? emprs.m_sze_fname : "<NULL>",
emprs.le_lnameStatus == adFldOK ?
emprs.m_sze_lname : "<NULL>");
// Restore original data because this is a demonstration.
if ((strcmp((char *)strOldFirst, emprs.m_sze_fname) &&
strcmp((char *)strOldLast, emprs.m_sze_lname))) {
pRstEmployees->Fields->GetItem("fname")->Value = strOldFirst;
pRstEmployees->Fields->GetItem("lname")->Value = strOldLast;
pRstEmployees->Update();
}
}
catch(_com_error &e) {
// Display errors, if any. Pass connection pointer accessed from the Recordset.
_variant_t vtConnect = pRstEmployees->GetActiveConnection();
// GetActiveConnection returns connect string if connection
// is not open, else returns Connection object.
switch(vtConnect.vt) {
case VT_BSTR:
PrintComError(e);
break;
case VT_DISPATCH:
PrintProviderError(vtConnect);
break;
default:
printf("Errors occurred.");
break;
}
}
// Clean up objects before exit. Release the IADORecordset Interface here
if (picRs)
picRs->Release();
if (pRstEmployees)
if (pRstEmployees->State == adStateOpen)
pRstEmployees->Close();
}
void UpdateX2() {
// Define ADO object pointers. Initialize pointers on define.
// These are in the ADODB:: namespace.
_ConnectionPtr pConnection = NULL;
_RecordsetPtr pRstEmployees = NULL;
// Define string variables.
_bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");
IADORecordBinding *picRs = NULL; // Interface Pointer declared
CEmployeeRs1 emprs; // C++ Class object.
try {
// Open a connection.
TESTHR(pConnection.CreateInstance(__uuidof(Connection)));
pConnection->Open(strCnn, "", "", NULL);
// Open recordset with data from Employee table.
TESTHR(pRstEmployees.CreateInstance(__uuidof(Recordset)));
pRstEmployees->CursorType = adOpenKeyset;
pRstEmployees->LockType = adLockOptimistic;
pRstEmployees->Open("employee", _variant_t((IDispatch*)pConnection,true),
adOpenKeyset, adLockOptimistic, adCmdTable);
pRstEmployees->AddNew();
_bstr_t strEmpID = "B-S55555M";
pRstEmployees->Fields->GetItem("emp_id")->Value = strEmpID;
pRstEmployees->Fields->GetItem("fname")->Value = (_bstr_t) ("Bill");
pRstEmployees->Fields->GetItem("lname")->Value = (_bstr_t) ("Sornsin");
// Show contents of buffer and get user input.
printf("\n\nAddNew in progress:\n\n");
printf("Data in buffer = %s , %s %s",
(LPSTR) (_bstr_t) pRstEmployees->Fields->GetItem("emp_id")->Value,
(LPSTR) (_bstr_t) pRstEmployees->Fields->GetItem("fname")->Value,
(LPSTR) (_bstr_t) pRstEmployees->Fields->GetItem("lname")->Value);
printf("\n\nUse Update to save buffer to recordset?(y/n):");
int chKey = _getch();
if ( toupper(chKey) == 'Y') {
pRstEmployees->Update();
// Open IADORecordBinding interface pointer for binding Recordset to a class.
TESTHR(pRstEmployees->QueryInterface(__uuidof(IADORecordBinding),(LPVOID*)&picRs));
// Bind the Recordset to a C++ Class here
TESTHR(picRs->BindToRecordset(&emprs));
// Go to the new record and show the resulting data.
printf ("\n\nData in recordset = %s , %s %s",
emprs.le_empidStatus == adFldOK ?
emprs.m_sze_empid : "<NULL>",
emprs.le_fnameStatus == adFldOK ?
emprs.m_sze_fname : "<NULL>",
emprs.le_lnameStatus == adFldOK ?
emprs.m_sze_lname : "<NULL>");
}
else {
pRstEmployees->CancelUpdate();
printf("\n\nNo new record added.\n");
}
// Delete new data because this is a demonstration.
_bstr_t strSQLDelete("DELETE FROM employee WHERE emp_id = '" + strEmpID + "'");
pConnection->Execute(strSQLDelete, NULL, adExecuteNoRecords);
}
catch(_com_error &e) {
// Display errors, if any. Pass connection pointer accessed from the Connection.
PrintProviderError(pConnection);
PrintComError(e);
}
// Clean up objects before exit. Release the IADORecordset Interface here
if (picRs)
picRs->Release();
if (pRstEmployees)
if (pRstEmployees->State == adStateOpen)
pRstEmployees->Close();
if (pConnection)
if (pConnection->State == adStateOpen)
pConnection->Close();
}
void PrintProviderError(_ConnectionPtr pConnection) {
// Print Provider Errors from Connection object.
// pErr is a record object in the Connection's Error collection.
ErrorPtr pErr = NULL;
if ( (pConnection->Errors->Count) > 0) {
long nCount = pConnection->Errors->Count;
// Collection ranges from 0 to nCount -1.
for ( long i = 0 ; i < nCount ; i++ ) {
pErr = pConnection->Errors->GetItem(i);
printf("Error number: %x\t%s\n", pErr->Number, (LPCSTR) pErr->Description);
}
}
}
void PrintComError(_com_error &e) {
_bstr_t bstrSource(e.Source());
_bstr_t bstrDescription(e.Description());
// Print Com errors.
printf("Error\n");
printf("\tCode = %08lx\n", e.Error());
printf("\tCode meaning = %s\n", e.ErrorMessage());
printf("\tSource = %s\n", (LPCSTR) bstrSource);
printf("\tDescription = %s\n", (LPCSTR) bstrDescription);
}