Is there any way (plugin, or otherwise) to put a formula as the value of a field, which would then self-update as the other fields it is based on are adjusted? Exactly the way field-calculator updates the value of the field, but instead of having to go back to field-calculator every time, it could just work like a spreadsheet when the layers it depends on are updated.
For example, if I want to find the number of housing units inside a polygon, I can do something in field calculator like
round("Density"*"Area"), but I have to redo it every time I adjust the polygon. When the calculations get more complicated it becomes a real hassle to manually go through and readjust manually.