ACC2000: How to Control Bound Form Transactions in Access Databases

This article shows you how use Data Access Objects (DAO) to control transactions in a form that is based on a table (a bound form) in a Microsoft Access (Jet) database.

Typically, a developer needs to be able to let users of a database application commit all or none of their data changes on a form. In versions of Access earlier than version 2000, you could not encapsulate data changes made on bound forms within transactions. This was because all transactions in bound forms were handled in a separate workspace, accessible only to Microsoft Access.

In Microsoft Access 2000, however, you can use a combination of Data Access Objects (DAO) and the new, form Recordset property to provide this capability. The example in this article assumes that the user wants to be prompted to commit all changes made to the form's data when the user closes the form. At that time, the user can either commit all of the changes or none of the changes.

Microsoft provides programming examples for illustration only, without warranty either expressed or implied. This includes, but is not limited to, the implied warranties of merchantability or fitness for a particular purpose. This article assumes that you are familiar with the programming language that is being demonstrated and with the tools that are used to create and to debug procedures. Microsoft support engineers can help explain the functionality of a particular procedure, but they will not modify these examples to provide added functionality or construct procedures to meet your specific requirements. NOTE: The sample code in this article uses Microsoft Data Access Objects. For this code to run properly, you must reference the Microsoft DAO 3.6 Object Library. To do so, click References on the Tools menu in the Visual Basic Editor, and make sure that the Microsoft DAO 3.6 Object Library check box is selected.

NOTE: This example is designed to work with single main forms. It is not designed to work with linked subforms.

Controlling Transactions on Bound Forms

1. Open the sample database Northwind.mdb.
2. Create a new form based on the Customers table.
3. Add all fields to the detail section of the form.
4. On the View menu, click Code to view the module of the form, and then add the following code to the module:

   Option Compare Database
   Option Explicit
   
   Private boolFrmDirty As Boolean
   Private boolFrmSaved As Boolean
   
   Private Sub Form_AfterDelConfirm(Status As Integer)
       If Me.Saved = False Then Me.Saved = (Status = acDeleteOK)
   End Sub
   
   Private Sub Form_AfterUpdate()
       Me.Saved = True
   End Sub
   
   Private Sub Form_Delete(Cancel As Integer)
       If Me.Dirtied = False Then DBEngine.BeginTrans
       Me.Dirtied = True
   End Sub
   
   Private Sub Form_Dirty(Cancel As Integer)
       If Me.Dirtied = False Then DBEngine.BeginTrans
       Me.Dirtied = True
   End Sub
   
   Private Sub Form_Open(Cancel As Integer)
       Dim db As DAO.Database
       Dim rs As DAO.Recordset
       Set db = CurrentDb
       Set rs = db.OpenRecordset("SELECT * FROM Customers", dbOpenDynaset)
       Set Me.Recordset = rs
   End Sub
   
   Private Sub Form_Unload(Cancel As Integer)
       Dim msg As Integer
       If Me.Saved Then
           msg = MsgBox("Do you want to commit all changes?", vbYesNoCancel)
           Select Case msg
               Case vbYes
                   DBEngine.CommitTrans
               Case vbNo
                   DBEngine.Rollback
               Case vbCancel
                   Cancel = True
           End Select
       Else
           If Me.Dirtied Then DBEngine.Rollback
       End If
   End Sub
   
   Public Property Get Dirtied() As Boolean
       Dirtied = boolFrmDirty
   End Property
   
   Public Property Let Dirtied(boolFrmDirtyIn As Boolean)
       boolFrmDirty = boolFrmDirtyIn
   End Property
   
   Public Property Get Saved() As Boolean
       Saved = boolFrmSaved
   End Property
   
   Public Property Let Saved(boolFrmSavedIn As Boolean)
       boolFrmSaved = boolFrmSavedIn
   End Property
   					

5. On the Debug menu, click Compile Northwind.
6. On the File menu, click Save Northwind.
7. When you are prompted, save the form as frmCustomers.
8. Open the frmCustomers form in Form view. Note that the form is populated with data.
9. Make some changes by editing an existing record, by inserting some new records, and by deleting some records.
10. Close the form. Note that you are prompted if you want to commit all changes.
11. Click No.
12. Open the form in Form view. Note that none of the changes that you made in step 9 were saved to the database.
13. Repeat steps 9 and 10.
14. When you are prompted to commit all changes, click Yes.
15. Open the form in Form view. Note that all the changes that you made were saved to the database.