この例では、Index の IndexNulls プロパティの機能を示します。コードでは、新規インデックスを作成し、ユーザーの入力に基づいて IndexNulls の値を設定します。Index は、Northwind Catalog の Employees Table に追加されます。新規 Index が Employees テーブルに基づいて Recordset に適用され、Recordset が開かれます。新規レコードが Employees テーブルに追加され、インデックス フィールドに Null 値を入れます。この新規レコードが表示されるかどうかは、IndexNulls プロパティの設定によって決まります。
#import "c:\Program Files\Common Files\system\ado\msadox.dll" \
no_namespace
#import "C:\Program Files\Common Files\System\ADO\msado15.dll" \
rename("EOF", "EndOfFile")
#include "iostream.h"
#include "stdio.h"
#include "conio.h"
#include "IndexNullsX.h"
// Function declarations
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);};
void IndexNullsX(_bstr_t);
//////////////////////////////////////////////////////////
// //
// Main Function //
// //
//////////////////////////////////////////////////////////
void main()
{
if(FAILED(::CoInitialize(NULL)))
return;
printf("\nShow records having indexed field value = NULL? (Y/N):");
char input = getche();
if(toupper(input)=='Y')
{
IndexNullsX("Allow");
}
else if(toupper(input)=='N')
{
IndexNullsX("Ignore");
}
else
{
exit(0);
}
::CoUninitialize();
}
//////////////////////////////////////////////////////////
// //
// IndexNullsX Function //
// //
//////////////////////////////////////////////////////////
void IndexNullsX(_bstr_t strSel)
{
HRESULT hr = S_OK;
// Define ADOX object pointers.
// Initialize pointers on define.
// These are in the ADOX:: namespace.
_CatalogPtr m_pCatalog = NULL;
_IndexPtr m_pIndexNew = NULL;
// Define ADODB object pointers
ADODB::_ConnectionPtr m_pCnn = NULL;
ADODB::_RecordsetPtr m_pRstEmployees = NULL;
// Define other variables
IADORecordBinding *picRs = NULL; // Interface Pointer Declared
CEmployeeRs emprs; // C++ Class Object
// Define string variable.
_bstr_t strCnn("Provider=Microsoft.Jet.OLEDB.4.0;"
"data source=c:\\Program Files\\Microsoft Office\\Office\\"
"Samples\\Northwind.mdb;");
try
{
TESTHR(hr = m_pCnn.CreateInstance(__uuidof(ADODB::Connection)));
TESTHR(hr = m_pCatalog.CreateInstance(__uuidof (Catalog)));
TESTHR(hr = m_pIndexNew.CreateInstance(__uuidof(Index)));
TESTHR(hr = m_pRstEmployees.CreateInstance(
__uuidof(ADODB::Recordset)));
// Connect the catalog.
m_pCnn->Open(strCnn,"","",NULL);
m_pCatalog->PutActiveConnection(_variant_t((IDispatch *)m_pCnn));
// Append Country column to new index.
m_pIndexNew->Columns->Append("Country",adVarWChar,0);
m_pIndexNew->Name = "NewIndex";
// Set IndexNulls based on user input
if(strcmp((LPSTR)strSel,"Allow")==0)
{
m_pIndexNew->IndexNulls = adIndexNullsAllow;
}
else if(strcmp((LPSTR)strSel,"Ignore")==0)
{
m_pIndexNew->IndexNulls = adIndexNullsIgnore;
}
// Append new index to Employees table
m_pCatalog->Tables->GetItem("Employees")->Indexes->Append(
_variant_t((IDispatch *)m_pIndexNew));
m_pRstEmployees->Index = m_pIndexNew->Name;
m_pRstEmployees->Open("Employees",
_variant_t((IDispatch *)m_pCnn),
ADODB::adOpenKeyset,ADODB::adLockOptimistic,
ADODB::adCmdTableDirect);
// Add a new record to the Employees table.
m_pRstEmployees->AddNew();
m_pRstEmployees->Fields->GetItem("FirstName")->Value =
(_bstr_t) "Gary";
m_pRstEmployees->Fields->GetItem("LastName")->Value =
(_bstr_t) "Haarsager";
m_pRstEmployees->Update();
// Bookmark the newly added record.
_variant_t varBookmark = m_pRstEmployees->Bookmark;
// Use the new index to set the order of the records.
m_pRstEmployees->MoveFirst();
printf("\n\nIndex = %s,",(LPSTR) m_pRstEmployees->Index);
printf("IndexNulls = %d\n\n",m_pIndexNew->IndexNulls);
cout<<"Country - Name"<<endl;
// Open an IADORecordBinding interface pointer which
// we will use for binding Recordset to a class
TESTHR(hr = m_pRstEmployees->QueryInterface(
__uuidof(IADORecordBinding),(LPVOID*)&picRs));
// Bind the Recordset to a C++ class here
TESTHR(hr = picRs->BindToRecordset(&emprs));
// Enumerate the Recordset.The value of the
// IndexNulls property will determine if the newly
// added record appears in the output.
while(!(m_pRstEmployees->EndOfFile))
{
printf("%s - %s %s\n",
emprs.lemp_CountryStatus == adFldOK ?
emprs.m_szemp_Country :"[Null]",
emprs.lemp_FirstNameStatus == adFldOK ?
emprs.m_szemp_FirstName :"<NULL>",
emprs.lemp_LastNameStatus == adFldOK ?
emprs.m_szemp_LastName :"<NULL>");
m_pRstEmployees->MoveNext();
}
// Delete new record because this is a demonstration.
m_pRstEmployees->Bookmark = varBookmark;
m_pRstEmployees->Delete(ADODB::adAffectCurrent);
m_pRstEmployees->Close();
// Delete new Index because this is a demonstration.
m_pCatalog->Tables->GetItem("Employees")->Indexes->
Delete(m_pIndexNew->Name);
m_pCatalog = NULL;
}
catch(_com_error &e)
{
// Notify the user of errors if any.
_bstr_t bstrSource(e.Source());
_bstr_t bstrDescription(e.Description());
printf("\n\tSource : %s \n\tdescription : %s \n ",
(LPCSTR)bstrSource,(LPCSTR)bstrDescription);
}
catch(...)
{
cout << "Error occured in include files...."<< endl;
}
}
IndexNullX.h
// IndexNullsX.h
#include "icrsint.h"
//This class extracts LastName,Country,FirstName from Employees table
class CEmployeeRs : public CADORecordBinding
{
BEGIN_ADO_BINDING(CEmployeeRs)
// Column LastName is the 2nd field in the table
ADO_VARIABLE_LENGTH_ENTRY2(2,adVarChar,m_szemp_LastName,
sizeof(m_szemp_LastName),lemp_LastNameStatus,TRUE)
// Column Country is the 11th field in the table
ADO_VARIABLE_LENGTH_ENTRY2(11,adVarChar,m_szemp_Country,
sizeof(m_szemp_Country),lemp_CountryStatus,TRUE)
// Column Country is the 17th field in the table
ADO_VARIABLE_LENGTH_ENTRY2(17,adVarChar,m_szemp_FirstName,
sizeof(m_szemp_FirstName),lemp_FirstNameStatus,TRUE)
END_ADO_BINDING()
public:
CHAR m_szemp_LastName[21];
ULONG lemp_LastNameStatus;
CHAR m_szemp_Country[16];
ULONG lemp_CountryStatus;
CHAR m_szemp_FirstName[11];
ULONG lemp_FirstNameStatus;
};