Use textbox to update database via MouseLeave

I have been evaluating Radzen Blazor for a week now. It is an amazingly powerful tool but I'm finding the documentation is a little behind so I'm having to ask newbie questions on the forum, for which I apologise.

I have a textbox displaying a text column "Grade" from a DB table (the record selected by a dropdown which writes the selected record to a page property "selectedRec").

The textbox value is ${selectedRec.Grade}. It changes OK when the dropdown is used.

How can I allow the user to type something new in this field, and have it update the database? Simply using the textbox "Change" event would not be good because that will also update every time a new record is selected from the dropdown (cannot distinguish between record change and user-entered edit). Do I need to have an associated "Save" button? (NB this is not a TemplateForm so I can't use a Submit button.) I thought I could use the MouseLeave event to do the update actions, using a condition comparing the current value with a saved property set by the dropdown, to check if the value has been changed by the user.

I have experimented with the MouseLeave event for a textbox. There does not seem to be any documentation, as the event was only added (to all components) a year ago. The designer seems to think the event args ${event} is type "string" - presumably equal to the current value of the textbox - but the generated code behind says it is of type ElementReference. How do I use this?