1. Designing & Building Business Applications Microsoft® Access Jerry Post
Chapter 7:
Database Integrity and Transactions
All Powder Board and Ski

2. Compute Sales Tax
Sales Tax
From Figure 6.17

3. Action Action Create a new module At the top add: Option Explicit
Add the function ComputeSalesTax
Use Debug/Compile to find errors
Close the module

4. Create Access Code Module
Visual Basic Editor
New Module
Application code

5. Action Action Edit the Sale form in Design view
Right click the SalesTax box and select the Build Code option
Select the Enter event
Add the line: SalesTax = ComputeSalesTax(Subtotal)
Run the form
Click on the SalesTax box to test the calculation

6. Add Event Code to the Sales Form
Choose the Enter event
Call the new function
Right click and Build Code

7. Debugging Use F8 to step through the code Set a break point
Roll the cursor over a variable to see its current value

8. Action Action Open the SaleItem subform in Design view
Open the form properties and modify the Record Source query to add the QuantityOnHand column
View the Field List box
Drag QuantityOnHand onto the form
Run the form and improve the layout

9. Adding QuantityOnHand to Subform
Build query to add QuantityOnHand
Right click to set properties
Drag QOH from Field List box onto form

10. Form Events Open a Form Forms Controls Close a Form 1) Open 2) Load
3) Resize
4) Activate
5) Current
6) Enter
7) GotFocus 12 a 12 a 12 a 33 33 33 d d d b b b
Forms
Controls
Close a Form
Change rows
5) Close
4) Deactivate
3) Unload
2) LostFocus
1) Exit 12 a 12 a 33 33 d d b b

11. Main Control Events control event 32 Enter 32 GotFocus
Change: keystrokes
131
time
Exit
131
LostFocus
131
BeforeUpdate
131
AfterUpdate
131

12. Action Action Edit the SaleItem subform in Design view
Right click the QOH box and build code
Select the AfterUpdate event
Add code to refresh the row and subtract QuantitySold from QuantityOnHand
Test the form

13. First Attempt: QOH Code
Private Sub QuantitySold_AfterUpdate()
Me.Refresh ‘ Save data for new rows
QuantityOnHand = QuantityOnHand - QuantitySold
End Sub

14. Problems
What if the clerk entered the wrong value and should have entered 1 instead of 2 units?
Test it, and the code subtracts 1 from the QOH, leaving 7.
You need to add the original 2 units back.
QuantityOnHand = QuantityOnHand – QuantitySold + OldQuantity

15. Clerk Changes SKU Subtract Inventory SKU QOH
Enter SKU , Quantity 2 8 10 8
Change SKU to
Add back to
Subtract for

16. Clerk Changes SKU: Events
Clerk enters original SKU (950049) and Quantity
Code subtracts QuantitySold from QuantityOnHand ( = 8)
Clerk changes SKU to new value (950050)
Active row becomes set for new value
Need to subtract QuantitySold from QuantityOnHand for
Need to add QuantitySold back into QuantityOnHand for
Private Sub cboSKU_Enter()
If IsNull(cboSKU.Value) Then
OldSKU = "-1"
Else
OldSKU = cboSKU.Value
End If
End Sub

17. Action Action Open the SaleItem subform in Design view
Choose View/Code
Add and modify the code as specified to handle changes in quantity
Test the form

18. SKU Changes: Code Private Sub cboSKU_Enter()
If IsNull(cboSKU.Value) Then
OldSKU = "-1"
Else
OldSKU = cboSKU.Value
End If
End Sub
Private Sub cboSKU_AfterUpdate()
If OldSKU <> "-1" And Not IsNull(QuantitySold) Then
QuantityOnHand = QuantityOnHand - QuantitySold
Dim sql As String
sql = "UPDATE Inventory SET QuantityOnHand = QuantityOnHand + " _
& QuantitySold & " WHERE SKU='" & OldSKU & "'"
Dim cmd As ADODB.Command
Set cmd = CreateObject("ADODB.Command")
cmd.ActiveConnection = CurrentProject.Connection
cmd.CommandText = sql
cmd.Execute

19. Delete Code Dim DelQuantity() As String Dim DelSKU() As String
Dim nDel As Integer
Private Sub Form_Delete(Cancel As Integer)
If IsNull(cboSKU.Value) Or IsNull(QuantitySold) Then Exit Sub
If (nDel = 0) Then
ReDim DelQuantity(Me.CurrentView)
ReDim DelSKU(Me.CurrentView)
End If
DelSKU(nDel) = cboSKU.Value
DelQuantity(nDel) = QuantitySold
nDel = nDel + 1
End Sub
Private Sub Form_AfterDelConfirm(Status As Integer)
Dim i As Integer
For i = 0 To nDel - 1
DeleteOneRow DelSKU(i), DelQuantity(i)
Next i
nDel = 0

20. Delete Code 2
Private Sub DeleteOneRow(ByVal SKU As String, ByVal Qty As String)
Dim sql As String
sql = "UPDATE Inventory SET QuantityOnHand = QuantityOnHand + " _
& Qty & " WHERE SKU='" & SKU & "'"
Dim cmd As ADODB.Command
Set cmd = CreateObject("ADODB.Command")
cmd.ActiveConnection = CurrentProject.Connection
cmd.CommandText = sql
cmd.Execute
End Sub

21. Action Action Open the SaleItem subform in Design view
Add the oldSKU variable
Add the SKU event code as described
Place a breakpoint in the code before the Execute line
Test the form by changing an SKU number
Examine the sql line before it runs
Add the delete code as shown
Test multiple changes to validate the code

22. Transactions for Discounts
New table

23. Rental Form
Button to open discount form

24. Action Action Create the Rental Discount form in Design view
Add the text boxes and button
Save the form
Open the Rental form in Design view
Add a button to open the Discount form
Modify the open code as indicated
Run the form and test the button

25. Rental Discount Form
RentID and Amount are filled in by code on the Rental form
Date default value is set to =Now()
This is an unbound form built from design view with no Record Source

26. Action Action Open the Rental Discount form in Design view
Add the specified code to the button click event
Test the forms

27. Rental Form Code: Discount Button
Private Sub cmdDiscount_Click()
On Error GoTo Err_cmdDiscount_Click
Dim stDocName As String
Dim stLinkCriteria As String
stDocName = "GiveRentDiscount"
DoCmd.OpenForm stDocName, , , stLinkCriteria
Forms!GiveRentDiscount!txtRentID = RentID
Forms!GiveRentDiscount!txtDiscountAmount = SubTotalCharges
Exit_cmdDiscount_Click:
Exit Sub
Err_cmdDiscount_Click:
MsgBox Err.Description
Resume Exit_cmdDiscount_Click
End Sub

28. Discount Code Private Sub cmdDiscount_Click() Dim cmd As ADODB.Command
Dim SQL1 As String, SQL2 As String
Set cmd = CreateObject("ADODB.Command")
cmd.ActiveConnection = CurrentProject.Connection
SQL1 = "UPDATE RentItem SET RepairCharges=0 WHERE RentID=" & txtRentID
SQL2 = "INSERT INTO RentalDiscount (RentID, DiscountDate, DiscountAmount, Reason)" & _
" VALUES (" & txtRentID & _
", #" & txtDiscountDate & "#" & _
", " & txtDiscountAmount & _
", '" & txtReason & "')"

29. Discount Code Continued
On Error GoTo Err_DiscountTrans
cmd.ActiveConnection.BeginTrans
cmd.CommandText = SQL1
cmd.Execute
cmd.CommandText = SQL2
cmd.ActiveConnection.CommitTrans
lblMessage.Caption = "Changes recorded."
Exit1:
Exit Sub
Err_DiscountTrans:
cmd.ActiveConnection.RollbackTrans
lblMessage.Caption = Err.Description
Resume Exit1
End Sub

30. Action Action Create a new query in Design view
Tables: Sale and SaleItem
Create column SaleWeek: Val(Format([SaleDate],”ww”))
Create column Value: [QuantitySold]*[SalePrice])
Sum the Value column

31. Query for Cursor: Weekly Sales
Val(Format([SaleDate],”ww”))

32. Action Action Create a new form in Design view Add a button
Add a text box named txtAverage
Add the specified code to the button
Run the form and test the code
Place a breakpoint and step through the code as it runs

33. Form to Compute Average Increase

34. Code to Compute Average Increase
Dim rst As ADODB.Recordset
Set rst = CreateObject("ADODB.Recordset")
Dim SQL As String
SQL = "SELECT SaleWeek, [Value] FROM qryWeeklySales"
rst.Open SQL, CurrentProject.Connection, adOpenStatic, adLockReadOnly
Dim avg1 As Double, n As Integer
Dim prior As Currency
prior = -1
Do Until rst.EOF
If (prior > 0) Then
avg1 = avg1 + (rst("Value") - prior) / prior
n = n + 1
End If
prior = rst("Value")
rst.MoveNext
Loop
rst.Close
Me.txtAverage = avg1 / n
Open the SQL statement or table
Skip the first week because there is no prior value
Compute the percent change and keep a running total
Save the current value and move to the next row

35. Keys: Create Sales and Items (barcode)
Customer ID card is scanned
Create new sale
Get SaleID
Scan an item
Save sale item, update QOH and totals
Save SaleID, SKU, Quantity
Repeat until done (payment key)

36. Action Action Create a new form in Design view
Add boxes for CustomerID, EmployeeID, SKU, and txtSaleID as the generated key
Create a command button and add the indicated code
Test the form
Place a breakpoint at the top of the code and step through the code

37. Generate Sale Form
IDs and SKU would be scanned, but to test code, set default values

38. Generate Sale Code-1
Dim sqlSale As String, sqlItem As String, sqlSaleItem As String
Dim rstSale As ADODB.Recordset, rstModel As ADODB.Recordset
Dim rstSaleItem As ADODB.Recordset
Set rstSale = CreateObject("ADODB.Recordset")
Set rstModel = CreateObject("ADODB.Recordset")
Set rstSaleItem = CreateObject("ADODB.Recordset")
sqlSale = "SELECT SaleID, CustomerID, EmployeeID, SaleDate FROM Sale"
sqlItem = "SELECT ModelID, ListPrice FROM Inventory INNER JOIN “ & _
“ItemModel ON Inventory.ModelID = ItemModel.ModelID “ & _
“WHERE SKU='" & SKU & "'"
sqlSaleItem = "SELECT SaleID, SKU, SalePrice, QuantitySold FROM SaleItem"
Dim cnn As ADODB.Connection
Set cnn = CurrentProject.Connection

39. Generate Sale Code-2 ' Get the List Price for the SKU
rstModel.Open sqlmodel, cnn, adOpenStatic, adLockReadOnly
Dim ListPrice As Currency
ListPrice = rstModel("ListPrice")
rstModel.Close
' Open the Sale table and create a new sale
rstSale.Open sqlSale, cnn, adOpenDynamic, adLockOptimistic
Dim SaleID As Long
rstSale.AddNew
rstSale("SaleDate") = Now
rstSale("CustomerID") = CustomerID
rstSale("EmployeeID") = EmployeeID
SaleID = rstSale("SaleID")
rstSale.Update
rstSale.Close

40. Generate Sale Code-3
' Add the SKU to the SaleItem table using the new SaleID
rstSaleItem.Open sqlSaleItem, cnn, adOpenDynamic, adLockOptimistic
rstSaleItem("SaleID") = SaleID
rstSaleItem("SKU") = SKU
rstSaleItem("SalePrice") = ListPrice
rstSaleItem("QuantitySold") = 1
rstSaleItem.Update
rstSaleItem.Close
txtSaleID = SaleID

41. Action Action Create a new form in Design view
Add a combo box to select customers
Add a text box to enter a new ZIP Code
Create a button and add the indicated code for it
Test the form

42. Lock Test Form
Combo box to select customer

43. Action
Action
Create a CustomerLocks form as a datasheet into the Customer table
Run the form
Edit a ZIP Code but do not leave the cell
Switch to the new form and run it for the same CustomerID
Return to the table and press the Tab key

44. CustomerLock Test Form

45. Optimistic Lock on the Form
Select the first customer, enter a ZIP code and change it
Change the ZIP but do not leave the cell
Switch back here and Tab out of the cell
Error message that value was changed

46. Action
Action
Switch to design view on the change form and add the specified error-handling code
Open the CustomerLocks form in Design view and set the Record Locks property to Edited Record
Run both forms
Change a ZIP Code in CustomerLocks
Enter a new ZIP Code in the change form for the same customer

47. Pessimistic Lock on Forms
Select the first customer, enter a ZIP code and change it
The change is not made and the error is trapped because the row is locked
Change the ZIP but do not leave the cell

48. Handle Optimistic Locks in Code
RetryUpdate:
rst.Open SQL, cnn, adOpenDynamic, adLockOptimistic
rst("ZIP") = NewZIPCode
rst.Update
rst.Close
Exit_cmdNewZipCode_Click:
Exit Sub
Err_cmdNewZipCode_Click:
If (MsgBox(Err.Description, vbRetryCancel) = vbCancel) Then
Resume Exit_cmdNewZipCode_Click
End If
rst.Cancel
rst.Requery
Resume RetryUpdate

49. Designing & Building Business Applications Microsoft® Access Jerry Post
End of Chapter 7