How to prevent duplicate records

[talktime]

we have a database of students, where we maintain their particulars specially fee fee history, i.e. which students have paid their fee and who have not yet paid. For this purpose we generate a fee slip every month.




When i click the 'Generate' button on the form, a required fee slip is generated for the selected month and student.
But the problem is that when i click the generate button again the same fee slip is generated again for the same selected month, which i don't want to be so. i want to change this behavior like if fee slip for a particulars month say May or June exists, the duplicate should not be generated if the button is click again and again.
i have provided the sample of Fee Slip Generate 'form' and 'report' to understand the problem.
i have also provided VBA code of the Generate button. please help.

Private Sub Command32_Click()

Dim dbs As Database
Dim Months As Integer
Dim mdate As Date

Set dbs = CurrentDb()
Me.Text26 = CDate("01" & "/" & Month(Me.Text26) & "/" & Year(Me.Text26))
Me.Text28 = CDate("01" & "/" & Month(Me.Text28) & "/" & Year(Me.Text28))
Months = Month(Me.Text26)
mdate = Me.Text26

If Me.Frame0.Value = 1 Then
DoCmd.OpenQuery "School Selected"
ElseIf Me.Frame0.Value = 2 Then
DoCmd.OpenQuery "Class Selected"
ElseIf Me.Frame0.Value = 3 Then
DoCmd.OpenQuery "Class&Section Selected"
ElseIf Me.Frame0.Value = 4 Then
DoCmd.OpenQuery "Student Selected"
End If

'MsgBox& Year(Me.Text28)
DoCmd.OpenQuery "Delete Transport Charges" ' Delete all those record have transport charges but no bus no.
DoCmd.OpenQuery "Delete Free Transport Records" ' Delete all those record have transport charges but FREE.
DoCmd.OpenQuery "Deduct Concession"
DoCmd.OpenQuery "Tuition Fee is zero" ' Delete where tuition fee =0

While mdate <= Me.Text28
dbs.Execute "Update [Tmp School] Set [Tmp School].[Fee Month] = '" & mdate & "'"
DoCmd.OpenQuery "School Append"
mdate = DateAdd("m", 1, mdate)
Wend

DoCmd.OpenQuery "Previous-Final"
dbs.Close

'DoCmd.OpenTable "Generated fee"
Me.Combo15.Enabled = False
Me.Combo19.Enabled = False
Me.Heads_subform.Enabled = False
MsgBox "Fee generated for the reqired Student(s)...", vbOKOnly
End Sub

[DepricatedZero]

The way I handle a similar situation is by using a unique indexed field that is a concatenation of the unique ID and the other unique elements.

So I have a table for Tasks, and a Task Log. Multiple copies of the same task can be in the task log, but only per day. So I concatenate taskID and executionDate for a unique key that says, basically, "task 17 was completed on Tuesday" (reads in the db as "17 - 5/14/2013")

[talktime]

Actually the database is created by someone else, he is not with us now, i don't know much about coding and the way concatenation works, if you could do something for me?

[June7]

DZ could be suggesting one of the following:

1. a compound primary key - TaskID and ExecutionDate fields in TaskLog would both be set as primary key, Index Yes No Duplicates

2. use code to save the TaskID and ExecutionDate as a single value in TaskLog

I lean toward option 1.

[talktime]

DZ could be suggesting one of the following:

1. a compound primary key - TaskID and ExecutionDate fields in TaskLog would both be set as primary key, Index Yes No Duplicates

2. use code to save the TaskID and ExecutionDate as a single value in TaskLog

I lean toward option 1.

could you help me June7, i can also send you my whole database a bit larger but downloadable. plz do something, i m need

[June7]

Did you try option 1? If you set both fields as primary key then Access won't allow records that duplicate that combination. Users will get a warning popup.

[talktime]

Did you try option 1? If you set both fields as primary key then Access won't allow records that duplicate that combination. Users will get a warning popup.

yes i tried but in-vain, tables are related together so it will not let me create primary keys or index on compound fields

[June7]

Try removing the link from the relationship builder, set primary keys, then reset the link.