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Microsoft OLE DB Simple Provider

The Microsoft OLE DB Simple Provider (OSP) allows ADO to access any data for which a provider has been written using the OLE DB Simple Provider (OSP) Toolkit. Simple providers are intended to access data sources that require only fundamental OLE DB support, such as in-memory arrays or XML documents.

To connect to the OLE DB Simple Provider DLL, set the Provider argument to the ConnectionString property to:

MSDAOSP

This value can also be set or read using the Provider property.

You can connect to simple providers that have been registered as full OLE DB providers by using the registered provider name, determined by the provider writer.

A typical connection string for this provider is:

"Provider=MSDAOSP;Data Source=serverName"

The string consists of these keywords:

Keyword

Description

Provider

Specifies the OLE DB provider for SQL Server.

Data Source

Specifies the name of a server.

The OLE DB Simple Provider (OSP) in MDAC 2.7 or later and Windows Data Access Components (Windows DAC) has been enhanced to support opening hierarchical ADO Recordsets over arbitrary XML files. These XML files may contain the ADO XML persistence schema, but it is not required. This has been implemented by connecting the OSP to the MSXML2.DLL; therefore MSXML2.DLL or later is required.

The portfolio.xml file used in the following example contains the following tree:

Portfolio
   Stock
      Shares
      Symbol
      Price
      Info
         Company Name
         WebSite

The XML DSO uses built-in heuristics to convert the nodes in an XML tree to chapters in a hierarchical Recordset.

Using these built-in heuristics, the XML tree is converted into a two-level hierarchical Recordset of the following form:

Parent Recordset
Shares, Symbol, Price, $Text
   Child Recordset
      Company Name, WebSite, $Text

Note that the Portfolio and Info tags are not represented in the hierarchical Recordset. For an explanation of how the XML DSO converts XML trees to hierarchical Recordsets, see the following rules. The $Text column is discussed in the following section.

The XML DSO follows a procedure for assigning elements and attributes to columns and rows in data-bound applications. XML is modeled as a tree with one tag that contains the entire hierarchy. For example, an XML description of a book could contain chapter tags, figure tags, and section tags. At the highest level would be the book tag, containing the subelements chapter, figure, and section. When the XML DSO maps XML elements to rows and columns, the subelements, not the top level element, are converted.

The XML DSO uses this procedure for converting the subelements:

  • Each subelement and attribute corresponds to a column in some Recordset in the hierarchy.

  • The name of the column is the same as the name of the subelement or attribute, unless the parent element has an attribute and a subelement with the same name, in which case a "!" is prepended to the subelement's column name.

  • Each column is either a simple column that contains scalar values (usually strings) or a Recordset column that contains child Recordsets.

  • Columns corresponding to attributes are always simple.

  • Columns corresponding to subelements are Recordset columns if either the subelement has its own subelements or attributes (or both), or the subelement's parent has more than one instance of the subelement as a child. Otherwise the column is simple.

  • When there are multiple instances of a subelement (under different parents), its column is a Recordset column if any of the instances imply a Recordset column; its column is simple only if all instances imply a simple column.

  • All Recordsets have an additional column named $Text.

The code that is needed to construct a Recordset is as follows:

   Dim adoConn as ADODB.Connection
   Dim adoRS as ADODB.Recordset

   Set adoRS = New ADODB.Connection
   Set adoRS = New ADODB.Recordset

   adoConn.Open "Provider=MSDAOSP; Data Source=MSXML2.DSOControl.2.6;"
   adoRS.Open "http://WebServer/VRoot/portfolio.xml, adoConn
NoteNote

The path of the data file can be specified by using four different naming conventions.

   'HTTP://
   adoRS.Open "http://WebServer/VRoot/portfolio.xml", adoConn
   'FILE://
   adoRS.Open "file:/// C:\\Directory\\portfolio.xml", adoConn
   'UNC Path
   adoRS.Open "\\ComputerName\ShareName\portfolio.xml", adoConn
   'Full DOS Path
   adoRS.Open "C:\Directory\portfolio.xml", adoConn

As soon as the Recordset has been opened, the usual ADO Recordset navigation commands can be used.

Recordsets generated by the OSP have a few limitations:

  • Client cursors (adUseClient) are not supported.

  • Hierarchical Recordsets created over arbitrary XML cannot be persisted using Recordset.Save.

  • Recordsets created with the OSP are read-only.

  • The XMLDSO adds an additional column of Data ($Text) to each Recordset in the Hierarchy.

For more information about the OLE DB Simple Provider, see Building a Simple Provider.

The following Visual Basic code demonstrates opening an arbitrary XML file, constructing a hierarchical Recordset, and recursively writing each record of each Recordset to the debug window.

Here is a simple XML file that contains stock quotes. The following code uses this file to construct a two-level hierarchical Recordset.

<portfolio>
   <stock>
      <shares>100</shares>
      <symbol>MSFT</symbol>
      <price>$70.00</price>
      <info>
         <companyname>Microsoft Corporation</companyname>
         <website>http://www.microsoft.com</website>
      </info>
   </stock>
   <stock>
      <shares>100</shares>
      <symbol>AAPL</symbol>
      <price>$107.00</price>
      <info>
         <companyname>Apple Computer, Inc.</companyname>
         <website>http://www.apple.com</website>
      </info>
   </stock>
   <stock>
      <shares>100</shares>
      <symbol>DELL</symbol>
      <price>$50.00</price>
      <info>
         <companyname>Dell Corporation</companyname>
         <website>http://www.dell.com</website>
      </info>
    </stock>
    <stock>
       <shares>100</shares>
       <symbol>INTC</symbol>
       <price>$115.00</price>
       <info>
          <companyname>Intel Corporation</companyname>
          <website>http://www.intel.com</website>
       </info>
   </stock>
</portfolio>

Following are two Visual Basic sub procedures. The first creates the Recordset and passes it to the WalkHier sub procedure, which recursively walks down the hierarchy, writing each Field in each record in each Recordset to the debug window.

Private Sub BrowseHierRecordset()
' Add ADO 2.7 or later to Project/References
' No need to add MSXML2, ADO just passes the ProgID through to the OSP.

    Dim adoConn As ADODB.Connection
    Dim adoRS As ADODB.Recordset
    Dim adoChildRS As ADODB.Recordset
        
    Set adoConn = New ADODB.Connection
    Set adoRS = New ADODB.Recordset
    Set adoChildRS = ADODB.Recordset

    adoConn.Open "Provider=MSDAOSP; Data Source=MSXML2.DSOControl.2.6;"
    adoRS.Open "http://bwillett3/Kowalski/portfolio.xml", adoConn
       
    Dim iLevel As Integer
    iLevel = 0
    WalkHier iLevel, adoRS
                          
End Sub

Sub WalkHier(ByVal iLevel As Integer, ByVal adoRS As ADODB.Recordset)
    iLevel = iLevel + 1
    PriorLevel = iLevel
    While Not adoRS.EOF
        For ndx = 0 To adoRS.Fields.Count - 1
            If adoRS.Fields(ndx).Name <> "$Text" Then
                If adoRS.Fields(ndx).Type = adChapter Then
                    Set adoChildRS = adoRS.Fields(ndx).Value
                    WalkHier iLevel, adoChildRS
                Else
                    Debug.Print iLevel & ": adoRS.Fields(" & ndx & _
                       ") = " & adoRS.Fields(ndx).Name & " = " & _
                       adoRS.Fields(ndx).Value
                End If
            End If
        Next ndx
        adoRS.MoveNext
    Wend
    iLevel = PriorLevel
End Sub
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