I totally agree: forms to easily manipulate data would be awesome!

My suggestion would be:
Allow us to create custom forms where records could be seen and edited, also with scripting for bulk automation.

Example use case:
1. Scan a barcode
2. The record shows on the screen
3. The "quantity" field gets decremented
4. The screen shows whether the action was a success or a failure
5. Ready to scan another record - without having had to click on a single button!

I really wish Memento could do it, because it is the best-looking and most practical database app I've seen so far, and I wouldn't like to have to get used to another one for this matter!

Partucularly from widget side for preset queries.

I had a look at the memento.db via sqlite debugger and there may be some way to do a work around for some basic operations, but would be fantastic in app