Passing keys from form to sub-form in Access - ms-access

Question

I'm using a sub-form to assign multiple tasks at the same time. This sub-form is placed on a form that has common details applicable to all the tasks there. For instance: Customer, Product Code, Part Code etc., Both the form and the sub-form feed the data to the same table. These forms are linked with one of the keys - Line Item, which is present on both the form and the sub-form. The other two keys are Task Title - placed on the sub-form, and Stage ID placed on the main form. Line Item is configured in a way that it populates the value from another open form for both the main form and the sub-form.
But Access isn't allowing me to add any details whatsoever to the sub-form. It gives me the error "You must enter a value for 'TableName.LineItem' field.
Kindly advise.

Answer 1

Two Approaches:
Select Table A and hit create form on the ribbon. Then do the usual prettification like deleting id columns, setting the forms format to continuous forms, and replacing textboxes with combo- boxes where appropriate.
First Approach is put unbound controls and a button in the header. Then insert the values from the controls in the button click event
Private Sub cmbAddRecord_Click()
Dim db As Database
Set db = CurrentDb
Dim rs As DAO.Recordset
Set rs = db.OpenRecordset("TableA")
rs.AddNew
rs!A = Me.txtA
rs!B = Me.txtB
rs!C = Me.txtC
rs.Update
Me.Requery 'show changes
rs.Close
db.Close
Set rs = Nothing
Set db = Nothing
End Sub
You can also insert values while actively entering the data for instance
Private Sub A_AfterUpdate() 'A is the TextBox in the detail section that is bound to A in TableA and so forth
Me.B = B.Parent!txtB
Me.C = C.Parent!txtC 'Tip use Me.MyControlName.SetFocus to select a control
Me.Refresh 'show changes
'tip you can also put this code in hotkeys https://learn.microsoft.com/en-us/office/vba/api/access.form.keydown
End Sub
'