Save and Open Methods Example (VC++)

Bài viết
11/18/2022
These three examples demonstrate how the Save and Open methods can be used together.
Assume you are going on a business trip and want to take along a table from a database. Before you go, you access the data as a Recordset and save it in a transportable form. When you arrive at your destination, you access the Recordset as a local, disconnected Recordset. You make changes to the Recordset, then save it again. Finally, when you return home, you connect to the database again and update it with the changes you made on the road.
// BeginSaveCpp.cpp  
// compile with: /EHsc  
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")  
  
#include <ole2.h>  
#include <stdio.h>  
#include <conio.h>  
#include <io.h>  
  
// Function declarations  
inline void TESTHR(HRESULT x) { if FAILED(x) _com_issue_error(x); };  
bool FileExists();  
void SaveX1();  
void SaveX2();  
void SaveX3();  
void PrintProviderError(_ConnectionPtr pConnection);  
void PrintComError(_com_error &e);  
  
int main() {  
   if ( FAILED(::CoInitialize(NULL)) )  
      return -1;  
  
   // If File exists in the specified directory, then display error  
   if (!FileExists()) {  
      SaveX1();  
      SaveX2();  
      SaveX3();  
   }  
  
   ::CoUninitialize();  
}  
  
// First, access and save the authors table.  
void SaveX1() {  
   HRESULT hr = S_OK;  
  
   // Define ADO object pointers.  Initialize pointers on define.  
   // These are in the ADODB::  namespace.  
   _RecordsetPtr pRstAuthors = NULL;  
  
   // Definitions of other variables  
   _bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source' ; Initial Catalog='pubs'; Integrated Security='SSPI';");  
  
   try {  
      TESTHR(pRstAuthors.CreateInstance(__uuidof(Recordset)));  
  
      pRstAuthors->Open("SELECT * FROM authors",strCnn, adOpenDynamic,   
         adLockBatchOptimistic, adCmdText);  
  
      // For sake of illustration, save the Recordset to a diskette in XML format.  
      pRstAuthors->Save("c:\\pubs.xml", adPersistXML);  
   }  
   catch(_com_error &e) {  
      // Notify the user of errors, if any.  
      // Pass a connection pointer accessed from the Recordset.  
      _variant_t vtConnect = pRstAuthors->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;  
      }  
   }  
  
   if (pRstAuthors)  
      if (pRstAuthors->State == adStateOpen)  
         pRstAuthors->Close();  
}  
  
// At this point, you have arrived at your destination.  
// You will access the authors table as a local, disconnected Recordset.   
// Don't forget you must have the MSPersist provider on the machine you   
// are using in order to access the saved file, c:\pubs.xml.  
void SaveX2() {  
   HRESULT hr = S_OK;  
  
   // Define ADO object pointers.  Initialize pointers on define.  
   // These are in the ADODB::  namespace.  
   _RecordsetPtr pRstAuthors = NULL;  
  
   try {  
      TESTHR(pRstAuthors.CreateInstance(__uuidof(Recordset)));  
  
      // For sake of illustration, we specify all parameters.  
      pRstAuthors->Open("c:\\pubs.xml", "Provider='MSPersist';", adOpenForwardOnly, adLockBatchOptimistic, adCmdFile);  
  
      // Now you have a local, disconnected Recordset.  
      // (In this example, changes will not be saved).  
      pRstAuthors->Find("au_lname = 'Carson'", NULL, adSearchForward);  
      if (pRstAuthors->EndOfFile) {  
         printf("Name not found ...\n");  
         pRstAuthors->Close();  
         return;  
      }  
      pRstAuthors->GetFields()->GetItem("City")->PutValue("Chicago");  
      pRstAuthors->Update();  
  
      // Save changes in ADTG format this time, purely for sake of  illustration.   
      // Note that the previous version is still on the diskette as c:\pubs.xml.  
      pRstAuthors->Save("c:\\pubs.adtg", adPersistADTG);  
   }  
   catch(_com_error &e){  
      // Notify the user of errors if any.  
      // Pass a connection pointer accessed from the Recordset.  
      _variant_t vtConnect = pRstAuthors->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;  
      }  
   }  
  
   if (pRstAuthors)  
      if (pRstAuthors->State == adStateOpen)  
         pRstAuthors->Close();  
}  
  
// Now update the database with changes.  
void SaveX3() {  
   HRESULT hr = S_OK;  
  
   // Define ADO object pointers.  Initialize pointers on define.  
   // These are in the ADODB::  namespace.  
   _RecordsetPtr pRstAuthors = NULL;  
   _ConnectionPtr pCnn = NULL;  
  
   // Definitions of other variables  
   _bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");  
  
   try {  
      TESTHR(pCnn.CreateInstance(__uuidof(Connection)));  
  
      TESTHR(pRstAuthors.CreateInstance(__uuidof(Recordset)));  
  
      // If there is no ActiveConnection, you can open with defaults.  
      pRstAuthors->Open("c:\\pubs.adtg", "Provider=MSPersist;",  
         adOpenForwardOnly, adLockBatchOptimistic, adCmdFile);  
  
      // Connect to the database, associate the Recordset with the connection,   
      // then update the database table with the changed Recordset.  
      pCnn->Open(strCnn, "", "", NULL);  
  
      pRstAuthors->PutActiveConnection(_variant_t((IDispatch *) pCnn));  
      pRstAuthors->UpdateBatch(adAffectAll);  
   }  
   catch(_com_error &e) {  
      // Notify the user of errors if any.  
      // Pass a connection pointer accessed from the Recordset.  
      _variant_t vtConnect = pRstAuthors->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;  
      }  
   }  
  
   if (pRstAuthors)  
      if (pRstAuthors->State == adStateOpen)  
         pRstAuthors->Close();  
   if (pCnn)  
      if (pCnn->State == adStateOpen)  
         pCnn->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);  
}  
  
bool FileExists() {  
   struct _finddata_t xml_file;  
   long hFile;  
  
   if( (hFile = _findfirst("c:\\pubs.xml", &xml_file )) != -1L)  
   {  
      printf( "File already exists!\n" );  
      return(true);  
   }  
   else  
      return (false);  
}
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Save and Open Methods Example (VC++)

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