How to Update all Related Records in Child when Parent Updated

[Margarita]

Hello,
I have to aapologize in adavance. If this is repeat topic- I am sorry- but I haven't been able to find the answer, most likely because I am using the wrong search terms. I am not very adept at creating forms and the form terminology is beyond me.
Here is the problem that I need help with:

I have a Transactions table which holds vendor name, invoice number, and amount.
I have an InvoiceDetails table which holds the details of the invoices.
The two tables have a relationship defined on InvoiceNum.
I set up an Invoices form based on 'select vendor, invoicenum, amount from transactions'. The records in this main form are updatable, as I expect.
I also set up a subform called InvoiceDetails and linked it to the main Invoices form through Vendor Name and InvoiceNum.
Ok, I can scroll through the vendors and the related records in the child form come up.
Now, I want the user to be able to edit the invoice numbers in the main form. I can do that since it's updatable.
What I cannot figure out is how to update all the related records in InvoiceDetails with the updated invoice number. Is this even possible? Or does the user have to go line by line in the InvoiceDetails subform and change the invoice numbers manually?
If this is possible, which events of the InvoiceNum control on the mainform do I have to use? I looked at posts about before and after update events, but I cannot figure out how to reference both the before-update value and the after-update value of the InvoiceNum field so that I can run an update query on the InvoiceDetails table to match what the user has just put into the InvoiceNum field of the main form.

Thank you! I really appreciate any insight or guidance anyone has to offer.

 

[John Big Booty]

Rather than link on the Invoice number as you are currently doing, use an AutoNumber Invoice ID (that will be static, and hidden), in that way the user can make changes to the Invoice header without impacting the link between the Parent and Child link.

The sample posted here may give you some inspiration.

 

[Margarita]

Rather than link on the Invoice number as you are currently doing, use an AutoNumber Invoice ID (that will be static, and hidden), in that way the user can make changes to the Invoice header without impacting the link between the Parent and Child link.

The sample posted here may give you some inspiration.

This should get you started.

Hi John,
Thanks so much for taking a look at this problem. I looked at the forms in the zipped sample, and that's pretty much the set up I have right now. I'm sorry if I'm being dense, but I don't undersatnd how a static invoice ID would help me update the related records in the child form. What I want to happen is this:

If the user is on Invoice number 1234A in the mainform, the relevant detailed for that invoice are displayed. But if, while viewing that record, the user modifies it to 1234AB, then I want the underlying table of Invoice Details to be updated as well- so that when the form is requried, the relevant invoice details are displayed for the now-updated invoice.

Am I missing some major part in the sample that you posted? Does it have that capability and I just couldn't figure it out?

Thanks again!

 

[John Big Booty]

If you link the Header and Detail records via a Static ID the user can change the Invoice number which is stored only in the Header to their hearts content, without you having to worry about how the Header and Detail are connected, as the invoice number is now not the linking factor.