ACC2: Sample Function Using Recursion to Display Data Tree

• Microsoft Access version 2.0

SUMMARY

This article demonstrates how you can create a sample user-defined Access Basic function that calls itself multiple times in order to loop through a linked list of items. You can use this technique to display data in a tree structure such as a directory of managers and employees.

This article assumes that you are familiar with Access Basic and with creating Microsoft Access applications using the programming tools provided with Microsoft Access. For more information about Access Basic, please refer to the "Building Applications" manual.

MORE INFORMATION

To create a sample user-defined Access Basic function that calls itself multiple times, follow these steps:

1. Open the sample database NWIND.MDB.

2. Make a copy of the Employees table and name it Employees2.

3. Open the Employees2 table in Design view.

4. Change the name of the Employee ID field to EmpID.

5. Change the name of the Reports To field to MgrID and set the MgrID field's Indexed property to Yes(Duplicates OK).

6. Save and close the Employees2 table.

7. Create a module and type the following line in the Declarations section:

         Option Explicit
   

8. Type the following two procedures:

         Function Start_List (EmpID As Long)
   

            Dim db As Database, rs As Recordset
            Set db = CurrentDB()
            Set rs = db.OpenRecordset("Employees2", DB_OPEN_TABLE)
            rs.Index = "Primarykey"
            rs.Seek "=", EmpID
            If rs.NoMatch Then Exit Function
            Debug.Print EmpID & " " & rs![first name] & " "; rs![last name]
            rs.Index = "MgrID"
            List_Employees rs, EmpID, 1
            rs.Close
            db.Close
   
         End Function
   
      NOTE: In the following sample code, an underscore (_) at the end of a
      line is used as a line-continuation character. Remove the underscore
      from the end of the line when re-creating this code.
   
            Sub List_Employees (rs As Recordset, ByVal MgrID As Long, ByVal _
            level As Integer)
   
            Dim bm As String
            rs.Seek "=", MgrID
            If rs.NoMatch Then Exit Sub
            Do While Not rs.EOF
              If rs!MgrID <> MgrID Then Exit Sub
              Debug.Print String$(level,9) & rs!EmpID & " " & rs! _
                    [first name]& " "; rs![last name]
              bm = rs.BookMark   ' Save place in the recordset.
              List_Employees rs, rs!EmpID, level + 1
              rs.BookMark = bm   ' Return to proper place for this level.
              rs.MoveNext
            Loop
   
         End Sub
   
   

9. To test this function, type the following line in the Immediate window, and then press ENTER:

         ? Start_List(2)
   

   Note that the records from the Employees2 table are displayed in a tree format of managers and employees as follows:

         2 Andrew Fuller
               1 Nancy Davolio
               3 Janet Leverling
                       11 Tim Smith
                       12 Caroline Patterson
               4 Margaret Peacock
               5 Steven Buchanan
                       6 Michael Suyama
                       7 Robert King
                       9 Anne Dodsworth
               8 Laura Callahan
               10 Albert Hellstern
               13 Justin Brid
                       14 Xavier Martin
   
   

REFERENCES

Microsoft Access "Building Applications," version 2.0, Chapter 11, "Working With Sets of Records," pages 242-267