I have looked at a number of other posts on this topic and tried many of the suggestions but have not had success.

In V11 CE, I want to add a custom field to sale.order that contains the backend url (not the  portal_url)  of the sale.order record.

I want to do this so I can reference the field in a custom email template to send to internal users alerting them to the details for a sale order. 

I want to send them an email from a given sale order using my custom template, so they can click on a link in the email and (assuming they are logged in) go directly to the sale order.

What code should I include in my .py file to create this custom field?

Thanks for reading.

Edit: I think the answer provided by Hilar Andikkadavath in the question linked below captures what I want to do, but I believe the answer relates to an older api and is herefore not compatible with V11.

\https://www.odoo.com/forum/help-1/how-to-get-the-current-url-in-email-template-110195