OLEDB Providers Enumeration
By: AdvanCode [2004-12-01]
Read: 3350 times
The question is: how can we get all OLEDB providers available? This could be done, relatively simply using VC++, but there aren't a simply solution for VB users. So, we'll try to make an ATL component to be used both in VC++ or VB projects.
There are at least 2 solutions for the problem - the first one is to use ADO and the other is using OLE DB interfaces.
Using ADO is simply to return an ADODB.Recordset containing all the informations. An example could be found here (Copyright 2002 Bob Beauchemin). Mainly, this is done like this (after you added ADO support):
STDMETHODIMP CGetProvRS::GetProvRS(VARIANT *pvRecordset)
{
Recordset20Ptr spRs;
ADORecordsetConstructionPtr spADOsCt;
VariantInit(pvRecordset);
CEnumerator cenum;
HRESULT hr;
// Root enumerator is the default
hr = cenum.Open();
if (FAILED(hr))
goto cleanup;
hr = spRs.CreateInstance(__uuidof(Recordset));
if (FAILED(hr))
goto cleanup;
hr = spRs->QueryInterface(__uuidof(ADORecordsetConstruction),
(void **)&spADOsCt);
if (FAILED(hr))
goto cleanup;
hr = spADOsCt->put_Rowset(cenum.m_spRowset);
if (FAILED(hr))
goto cleanup;
pvRecordset->vt = VT_DISPATCH;
pvRecordset->pdispVal = (IDispatch*)spRs.Detach();
cleanup:
cenum.Close();
return hr;
}
Doing so, the method is returning an ADODB.Recordset that can be used in VB applications, for instance. The names of the fields returned are:
col 0: size 4 type DBTYPE_UI4 col 1: name SOURCES_NAME size 255 type DBTYPE_WSTR col 2: name SOURCES_PARSENAME size 255 type DBTYPE_WSTR col 3: name SOURCES_DESCRIPTION size 255 type DBTYPE_WSTR col 4: name SOURCES_TYPE size 2 type DBTYPE_UI2 col 5: name SOURCES_ISPARENT size 2 type DBTYPE_BOOL col 6: name SOURCES_CLSID size 255 type DBTYPE_WSTR
All the details can be found here.
A VB example of using the component could be as below:
Dim rs As Recordset
Dim provrs As New GetProvRS
Dim i As Integer
Set rs = provrs.GetProvRS()
While Not rs.EOF
For i = 0 To rs.Fields.Count - 1
Debug.Print "Field: " & rs(i).Name & " = " & rs(i).Value
Next i
Debug.Print
rs.MoveNext
Wend
The other solution is by using OLEDB interfaces, directly, as presented in "Teach Yourself Database Programming with Visual C++ 6 in 21 Days" (cap. 17), from Sams Publishing or this example from Microsoft KB (in italian).
Below, there is the source code for an ATL component that return all providers as variant-array, which is simply to use in VB. Create a new component using ATL COM AppWizard and add a new ATL object called "Providers". Include the libraries and the constants as below (in Providers.cpp):
#include#include #include typedef struct EnumProvidersRow { UINT num; char SourceName[255]; char ParseName[255]; char SourceDesc[255]; USHORT SourceType; BOOL IsParent; char SourceCLSID[255]; } ENUMPROVIDERSROW; #define COLS 7 #define ROWS 10
Then add the following code in a new created method called GetProviders([out, retval] VARIANT* res):
STDMETHODIMP CProviders::GetProviders(VARIANT *res)
{
// TODO: Add your implementation code here
ISourcesRowset* pSrcRowset;
IRowset* pRowset;
IAccessor* pAccessor;
HACCESSOR hAccessor;
ENUMPROVIDERSROW Rows;
DBBINDING Binding[COLS];
DBBINDSTATUS BindingStatus[COLS];
ULONG Feched;
HROW* phRow = new HROW[ROWS];
ZeroMemory( &Binding[0], sizeof(DBBINDING) * COLS);
HRESULT hr = CoCreateInstance(CLSID_OLEDB_ENUMERATOR, NULL,
CLSCTX_INPROC_SERVER, IID_ISourcesRowset, (LPVOID*)&pSrcRowset);
if( hr == S_OK )
{
hr = pSrcRowset->GetSourcesRowset( NULL, IID_IRowset, 0, NULL,
(LPUNKNOWN*)&pRowset);
pSrcRowset->Release();
if( hr == S_OK )
{
hr = pRowset->QueryInterface(IID_IAccessor, (LPVOID*)&pAccessor);
if( hr == S_OK )
{
Binding[0].iOrdinal = 0;
Binding[0].obValue = offsetof(ENUMPROVIDERSROW, num);
Binding[0].dwPart = DBPART_VALUE;
Binding[0].dwMemOwner = DBMEMOWNER_CLIENTOWNED;
Binding[0].eParamIO = DBPARAMIO_NOTPARAM;
Binding[0].wType = DBTYPE_UI4;
Binding[1].iOrdinal = 1;
Binding[1].obValue = offsetof(ENUMPROVIDERSROW, SourceName);
Binding[1].dwPart = DBPART_VALUE;
Binding[1].dwMemOwner = DBMEMOWNER_CLIENTOWNED;
Binding[1].eParamIO = DBPARAMIO_NOTPARAM;
Binding[1].wType = DBTYPE_STR;
Binding[1].cbMaxLen = 255;
Binding[2].iOrdinal = 2;
Binding[2].obValue = offsetof(ENUMPROVIDERSROW, ParseName);
Binding[2].dwPart = DBPART_VALUE;
Binding[2].dwMemOwner = DBMEMOWNER_CLIENTOWNED;
Binding[2].eParamIO = DBPARAMIO_NOTPARAM;
Binding[2].wType = DBTYPE_STR;
Binding[2].cbMaxLen = 255;
Binding[3].iOrdinal = 3;
Binding[3].obValue = offsetof(ENUMPROVIDERSROW, SourceDesc);
Binding[3].dwPart = DBPART_VALUE;
Binding[3].dwMemOwner = DBMEMOWNER_CLIENTOWNED;
Binding[3].eParamIO = DBPARAMIO_NOTPARAM;
Binding[3].wType = DBTYPE_STR;
Binding[3].cbMaxLen = 255;
Binding[4].iOrdinal = 4;
Binding[4].obValue = offsetof(ENUMPROVIDERSROW, SourceType);
Binding[4].dwPart = DBPART_VALUE;
Binding[4].dwMemOwner = DBMEMOWNER_CLIENTOWNED;
Binding[4].eParamIO = DBPARAMIO_NOTPARAM;
Binding[4].wType = DBTYPE_UI2;
Binding[5].iOrdinal = 5;
Binding[5].obValue = offsetof(ENUMPROVIDERSROW, IsParent);
Binding[5].dwPart = DBPART_VALUE;
Binding[5].dwMemOwner = DBMEMOWNER_CLIENTOWNED;
Binding[5].eParamIO = DBPARAMIO_NOTPARAM;
Binding[5].wType = DBTYPE_BOOL;
Binding[6].iOrdinal = 6;
Binding[6].obValue = offsetof(ENUMPROVIDERSROW, SourceCLSID);
Binding[6].dwPart = DBPART_VALUE;
Binding[6].dwMemOwner = DBMEMOWNER_CLIENTOWNED;
Binding[6].eParamIO = DBPARAMIO_NOTPARAM;
Binding[6].wType = DBTYPE_STR;
Binding[6].cbMaxLen = 255;
hr = pAccessor->CreateAccessor( DBACCESSOR_ROWDATA, COLS,
&Binding[0], 0, &hAccessor, &BindingStatus[0]);
if( hr == S_OK )
{
hr = pRowset->RestartPosition( DB_NULL_HCHAPTER );
while(true)
{
hr = pRowset->GetNextRows( DB_NULL_HCHAPTER, 0, ROWS,
&Feched, &phRow);
if( (hr == S_OK || hr == DB_S_ENDOFROWSET) && Feched )
{
SAFEARRAYBOUND MyBound[2];
MyBound[0].cElements = Feched-2; //first item lost
MyBound[1].cElements = Feched-2;
MyBound[0].lLbound = 0;
MyBound[1].lLbound = 0;
res->vt = VT_VARIANT | VT_ARRAY;
res->parray = SafeArrayCreate(VT_VARIANT,2,MyBound);
long MyPosition[2];
VARIANT tmp;
VariantInit(&tmp);
for(int i=0; i<(int)Feched; i++)
{
pRowset->GetData( phRow[i], hAccessor,
(LPVOID)&Rows);
MyPosition[0] = i;
MyPosition[1] = 0;
tmp.vt =VT_BSTR;
tmp.bstrVal = SysAllocString(A2BSTR(Rows.SourceName));
SafeArrayPutElement(res->parray,MyPosition,&tmp);
MyPosition[1] = 1;
SysFreeString(tmp.bstrVal);
tmp.bstrVal = SysAllocString(A2BSTR(Rows.ParseName));
SafeArrayPutElement(res->parray,MyPosition,&tmp);
MyPosition[1] = 2;
SysFreeString(tmp.bstrVal);
tmp.bstrVal = SysAllocString(A2BSTR(Rows.SourceDesc));
SafeArrayPutElement(res->parray,MyPosition,&tmp);
MyPosition[1] = 3;
SysFreeString(tmp.bstrVal);
tmp.vt = VT_I2;
tmp.iVal = Rows.SourceType ;
SafeArrayPutElement(res->parray,MyPosition,&tmp);
MyPosition[1] = 4;
tmp.vt = VT_BOOL;
tmp.boolVal = Rows.IsParent ;
SafeArrayPutElement(res->parray,MyPosition,&tmp);
MyPosition[1] = 5;
tmp.vt = VT_BSTR;
tmp.bstrVal = SysAllocString(A2BSTR(Rows.SourceCLSID));
SafeArrayPutElement(res->parray,MyPosition,&tmp);
SysFreeString(tmp.bstrVal);
}
pRowset->ReleaseRows( Feched, phRow, NULL, NULL, NULL);
if( hr == DB_S_ENDOFROWSET)
break;
}
else
break;
}
pAccessor->ReleaseAccessor( hAccessor, NULL);
}
pAccessor->Release();
}
pRowset->Release();
}
}
delete[] phRow;
return hr;
}
To use it in a VB project is straightforward - add a reference to "AllProvs 1.0 Type Library" and add the code:
Dim x As New ALLPROVSLib.Providers
Private Sub Command1_Click()
Dim a As Variant
a = x.GetProviders
For i = 0 To UBound(a, 1)
For j = 0 To UBound(a, 2)
Debug.Print a(i, j) & " - ";
Next
Debug.Print
Next
End Sub
原文网址：http://www.advancode.com/articles.php?page=oledbproviders