INFO: ADO Hierarchical Recordsets via SHAPE APPEND via C++/VBA/Java

MORE INFORMATION

Hierarchical recordsets present an alternative to using JOIN syntax when accessing parent-child data. Hierarchical recordsets differ from a JOIN in that with a JOIN, both the parent table fields and child table fields are represented in the same recordset. With a hierarchical recordset, the recordset contains only fields from the parent table. In addition, the recordset contains an extra field that represents the related child data, which you can assign to a second recordset variable and traverse.

Hierarchical recordsets are made available via the MSDataShape provider, which is implemented by the client cursor engine.

A new clause, SHAPE, is provided to relate SELECT statements in a hierarchical fashion. The syntax is summarized below:

   SHAPE {parent-command} [[AS] name]
   APPEND ({child-command} [[AS] name] RELATE parent-field TO child-field)
   [,({child2-command} ...)]
				

Note

• By default, the child recordsets in the parent recordset will be called Chapter1, Chapter2, etc., unless you use the optional [[AS] name] clause to name the child recordset.
• You can nest the SHAPE command. The {parent-command} and/or {child-command} can contain another SHAPE statement.
• The {parent-command} and {child-command} do not have to be SQL SELECT statements. They can use whatever syntax is supported by data provider.

The example below illustrates a hierarchical recordset using the publishers and titles tables in the SQL Server pubs database. The same code could easily be modified to use the Biblio Microsoft Access database that ships with Visual Studio. (You would need to change the SHAPE syntax and debug print for two fields: PUB_ID to PUBID and PUB_NAME to NAME.)

Microsoft provides programming examples for illustration only, without warranty either expressed or implied, including, but not limited to, the implied warranties of merchantability and/or fitness for a particular purpose. This article assumes that you are familiar with the programming language being demonstrated and the tools used to create and debug procedures.

VBA Example

This step-by-step example is written for Visual Basic, but could be used in Microsoft Access just as easily.

1. Create a new VBA project and add a form named Form1 and a command button named Command1.
2. Add a reference to the Microsoft ActiveX Data Objects Library.
3. Add the following code to the form:
   
   Note You must change User UID=<username> and PWD=<strong password> to the correct values before you run this code. Make sure that UID has the appropriate permissions to perform this operation on the database.

         Private Sub Command1_Click()
           Dim cn As ADODB.Connection, rsPub As ADODB.Recordset, _
             rsTitle As ADODB.Recordset, SQL As String
           Set cn = New ADODB.Connection
           Set rsPub = New ADODB.Recordset
           cn.Provider = "MSDataShape"
           cn.Open "dsn=Pubs;uid=<username>;pwd=<strong password>;database=pubs"
           SQL = "SHAPE {SELECT * FROM publishers} APPEND " & _
                 "({SELECT * FROM titles} AS PubTitles " & _
                 "RELATE pub_id TO pub_id)"
           rsPub.Open SQL, cn, adOpenStatic, adLockReadOnly, adCmdText
           Do While Not rsPub.EOF
             Debug.Print "Publisher", rsPub!pub_name
             Set rsTitle = rsPub!PubTitles.Value
             Do While Not rsTitle.EOF
               Debug.Print , rsTitle!Title
               rsTitle.MoveNext
             Loop
             rsTitle.Close
             rsPub.MoveNext
           Loop
           rsPub.Close
           cn.Close
           Set rsTitle = Nothing
           Set rsPub = Nothing
           Set cn = Nothing
         End Sub
   					

4. Run the form and click the command button. The list of publishers and titles will be displayed in the Debug/Immediate window.