How to update a subform after performing a DELETE query? - ms-access

Question

I have a form, myForm, that includes a subform, mySubform. The records in mySubform have a many to one relationship with the record source of the myForm, as expected, and There is a combobox in mySubform, myCombo, whose values is linked to one of the columns of the record source of mySubform.
I have been having difficulty to delete a record in mySubform, by erasing the current value in myCombo. I have put the code below under the OnChange event of myCombo (after trying many different alternatives).
Please not that I have simplified the delete query and the actual one works fine in the back-end (SQL Server). However, after performing the delete operation, I get this error when the execution reaches Me.Requery:
Error 3162 You tried to assign a Null value to a variable that is not a Variant data type.
Also, after having the degugger skip the Me.Requery and going back to the form, the deleted record shows "#DELETED" in every combobox and textbox for that particular record, and mySubform is not any good beyond that point.
I have looked up very many resources and tried different statements instead of Me.Requery, but none has worked so far. Help is much appreciated.
Private Sub myCombo_Change()
If IsNull(Me.myCombo.Text) Or Me.myCombo.Text = vbNullString Then
Dim strSql As String
strSql = "DELETE FROM mySubformRecordSource WHERE PrimaryKeyColumn= " & theCurrentPrimaryKeyValueForTheValueIn_MyCombo
CurrentDb.Execute strSql
Me.Requery
End If
End Sub

Answer 1

I solved the problem by putting Me.Dirty = False after reading this discussion:
Editing Record issues in Access / SQL (Write Conflict)
Private Sub myCombo_Change()
If IsNull(Me.myCombo.Text) Or Me.myCombo.Text = vbNullString Then
Me.Dirty = False
Dim strSql As String
strSql = "DELETE FROM mySubformRecordSource WHERE PrimaryKeyColumn= " & theCurrentPrimaryKeyValueForTheValueIn_MyCombo
CurrentDb.Execute strSql
Me.Requery
End If
End Sub
The form and subform work flawlessly now, but I still dont quite understand the complete logic behind the solution. It has something to do with Me.Dirty=False saving the changes to the content of a non-nullable (or nullable, both work fine) column before programmatically delete the entire record. How exactly though, I dont know and will appreciate input.

Answer 2

Not entering on the choices of used cursors etc I think that the solution could be simply "requery" the parent form called by the code of the subform.
But i also have found similar situation in past projects that i made (sorry not beeing exaustive, i'm not using VBA anymore) and the requery command was done on subform but from the main form code, something like this:
If local_procedures.deleteContratto(anagrafica_id_par, servizio_id_par) = OK Then
Me.subfrm_contratti_frm_anagrafica.Requery
...
In this case you could delegate parent form to call delete procedure and update logic (.Requery) of the child form, by mean of an event raised from subForm listen on parent for example.
For the sake of completeness i started hinting about cursors because i think it's the underlying reason for these kind of sync failures between recordsets, the parent form one and the child form one.
There are many advices about using dbSeeChanges with db.Execute on SQL Server backend and the resulting default cursors.
UPDATE
Here's a code snippet where a custom event is raised from child to be caught from parent that is delegated to execute code regarding the child.
This pattern doesn't break the parent-child/one-to-many logic, assuming parent has more decision power than child.
' in mySubform
' assuming theCurrentPrimaryKeyValueForTheValueIn_MyCombo is a Long ID
Public Event DeleteRequest(record_ID As Long)
Private Sub myCombo_Change()
If IsNull(Me.myCombo.Text) Or Me.myCombo.Text = vbNullString Then
RaiseEvent DeleteRequest(theCurrentPrimaryKeyValueForTheValueIn_MyCombo)
End If
End Sub
' in myForm
Private WithEvents frmMySubform As Form__mySubform
' you could have more instances of mySubform concerning different issues or subrecords and manage each one correctly ...
Private WithEvents frmMySubform2nd As Form__mySubform
Private Sub frmMySubform_DeleteRequest(record_ID As Long)
Dim strSql As String
strSql = "DELETE FROM mySubformRecordSource WHERE PrimaryKeyColumn= " & record_ID
CurrentDb.Execute strSql
With Me.frmMySubform.Form
.Requery
' ...
end With
End Sub
Private Sub frmMySubform2nd_DeleteRequest(record_ID As Long)
Dim strSql As String
strSql = "DELETE FROM my2ndSubformRecordSource WHERE PrimaryKeyColumn= " & record_ID
CurrentDb.Execute strSql
With Me.frmMySubform2nd.Form
.Requery
' ...
end With
End Sub