Show error message on wrong db version

[moving-bits]

Not sure if it's possible technically, but it would be useful:

cgeo should never crash even with an newer DB version. There should be a message saying "newer DB version in backup, can not read backup, please update cgeo version".

Originally posted by @geocachermgo in #8876 (comment)

I'll add to this: Error instead of crash should also be the case when downgrading c:geo reusing the existing database stored internally, without doing an explicit restore.

[eddiemuc]

DB version can be retrieved for a DB by executing pragma user_version. My PR for #2553 contains a method for this in DataStore

[moving-bits]

DB version can be retrieved for a DB by executing pragma user_version. My PR for #2553 contains a method for this in DataStore

It's even easier, there is a getVersion() method :-)

I'm currently creating a PR for part 1, checking DB version before trying a restore.

[eddiemuc]

It's even easier, there is a getVersion() method :-)

Damn :-) Ok I did not know that...

[moving-bits]

Damn :-) Ok I did not know that...

Me neither, before I stumbled upon it in the docs today :-)

[moving-bits]

Part 1 is implemented with #8908 - Check database version before trying a database restore.

Part 2 needs to be explored yet - Check database version on startup and display a meaningful message if db version is not compatible - instead of just crashing.

[moving-bits]

As for part 2:

• A check "current db version <= expected db version" may work (to be explored yet),
• but for the case "current db version > expected db version" we need to check whether it is downgradeable, but for this we need to open the database - bamm!

Thus we could only display a warning message in this case (if at all), stating that

• there is a version mismatch,
• and we try to downgrade the database,
• and inform the user what to do (or where to look) if it fails.

Alternatively we need to find a way to open the database without automatic upgrading/downgrading, to be able to read the extension table only, and then do the "is downgradeable" check.

[eddiemuc]

Alternatively we need to find a way to open the database without automatic upgrading/downgrading, to be able to read the extension table only, and then do the "is downgradeable" check.

Is is possible/feasible to simply first open the db with SQLiteDatabase.openDatabase (without using any DBHelper and version-upgrade/downgrade), then perform the necessary checks and continue only afterwards with the "full" DBHelper?
Granted, this adds startup time for opening the DB, can't tell whether this is a problem.