To have a sure response at my question i have tryed myself with my app:
1) I have uploaded to the Ubuntu store the new version of the app
2) I have updated the old app version (already installed on my Tablet) with the new one (using the ubuntu update features of the tablet)
the old Database created by the old app version was NOT reused by the new App: a new blank one was created (NO modification was made to the database structure).
I have verified that the old database was NOT lost (is mantained in the file system).
The Databases created with U1Db QML API are placed in a folder under this path:
"applicationName" is the value inserted in the field 'applicationName' inside Main.qml of the source code
"version" is the application version (eg: 1.1)
"NameApplication" is the name of the App
So that that the database for old App version 1.0 is inside:
And the one for the new version 1.1 is inside:
To use the old database is necessary copy the Database file from the old folder to the new one, overwriting the other one. To do do this is possbile use the Terminal app or with the File Manager of the Tablet (after enabling the option to show the hidden folders in the File manager menu (.local is an hidden folder in the home one)).
I have verified that creating the database without QT.resolveurl("..."):
the database file will be placed in the folder:
without any references at the application verion number.
So that i think that the right solution is NOT use QT.resolvedUrl() to prevent problems in case of App updates.
So, the new question is: how is possible create and export/import content from a DB file ?
Seem that using the U1DB QML API is not possible....