INF: How to Use OLE DB Sample Text Provider in ADO

MORE INFORMATION

The OLE DB SDK installs a sample text OLE DB provider that allows you to access text files. This sample text provider is located in the Samples\Sampprov directory. To use this sample text provider in ADO, you need to change the source code of the sample text provider, and you also need to change the ADO threading model. To do this, perform the following steps:

1. Modify the SetProperties function in the CutilProp class. The source file that contains this function is Utilprop.cpp. Change the last line of this function to return DB_E_ERRORSOCCURRED instead of E_FAIL. The complete line is:

   return ResultFromScode( DB_E_ERRORSOCCURRED  );
   						

   ADO returns an error if the underline providers return E_FAIL when setting the OLE DB properties. The sample text driver needs to return DB_E_ERRORSOCCURRED instead of E_FAIL if there are any unsupported properties encountered.
2. The ADO threading model needs to be either "apartment" or "both." The default threading model is the apartment model. The sample text provider does not register any threading model, so it defaults to a single-threaded model. The threading models needs to match up in order for ADO to communicate with the sample text provider. After changing the threading model, you will need to restart Internet Information Server (IIS) for the changes to take effect.

You can use the batch file that came with the OLE DB SDK 1.1 to change the ADO apartment model. These files are located in the Bin\Util OLEDBSDK directory. The Makeapt batch file sets ADO to be apartment model threaded. You can create a REG file base on the following code and merge it with the registry to change the ADO threading model to both:

WARNING: Modifying the registry incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.

   REGEDIT4

   [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{0000022C-0000-0010-8000-
   00AA006D2EA4}\InprocServer32]
   "ThreadingModel"="Both"

   [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{00000231-0000-0010-8000-
   00AA006D2EA4}\InprocServer32]
   "ThreadingModel"="Both"

   [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{00000280-0000-0010-8000-
   00AA006D2EA4}\InprocServer32]
   "ThreadingModel"="Both"

   [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{00000281-0000-0010-8000-
   00AA006D2EA4}\InprocServer32]
   "ThreadingModel"="Both"

   [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{00000293-0000-0010-8000-
   00AA006D2EA4}\InprocServer32]
   "ThreadingModel"="Both"
				

After you finish the two steps listed above, you can use the following Visual Basic code to use the sample text provider to retrieve data from a text file in ADO:

   Private Sub myTest()
        Dim con As New ADODB.Connection
        Dim rs As ADODB.Recordset

        ' data source specifies path that contains customer.csv
        con.Open "provider=sampprov;data
   source=c:\\sdks\\oledbsdk\\samples\\sampclnt\\"
        Set rs = con.Execute("customer.csv")

        For i = 0 To rs.Fields.Count - 1
            Print rs.Fields(i).Name
        Next i
        While Not rs.EOF
            Debug.Print rs(0)
            rs.MoveNext
        Wend
   End Sub