[SailfishDevel] Sharing a common OfflineStorage DB between multiple Sailfish apps.

[Thomas Perl]

Hi,

On 16 Jan 2014, at 13:14, christopher.lamb at thurweb.ch wrote:
> This gives the following Application Output:
> [D] main:42 - offlineStoragPath orig:  "/home/nemo/.local/share/CreateDBQt5/QML/OfflineStorage"
> [D] main:44 - offlineStoragPath new:  "/home/nemo/.local/share/landed25_QT5/QML/OfflineStorage"
> 
> The database is indeed created in /home/nemo/.local/share/landed25_QT5/QML/OfflineStorage", and is accessible to the app landed25_QT5
> 
> Note the order of the view->engine()->setOfflineStoragePath... and view->setSource... calls is crucial. If the setSource comes first, then the QML is initiated before the storagePath is changed!
> 
> In my next experiment I will try to change the storageLocation to something like QStandardPaths::GenericDataLocation.
> 
> The question on harbour acceptability remains ...

For Harbour, using QStandardPaths should always be safe, but append the name of your application (harbour-myapp) to the path, so that all your application-specific data ends up there. Note that there is (in line with XDG) the data directory (where you store data, e.g. documents or something), the config directory (where you store configuration options, e.g. enabled/disabled states of features) and the cache directory (where you store data that can be safely deleted in case of low disk uage - e.g. user avatars from a web service or previews/thumbnails of documents, etc… - everything that can be re-created easily).

This is important, as this can be used in the future from a system service to calculate per-app disk usage and allow clearing of application data, integration with backup, etc… - also, it’s easier for power users to SSH into the device and find where their user data is. If you use QStandardPaths or XDG, you can be sure that if (when) the data location changes in the future, your application will still work correctly.

Absolute no-no: Hardcoding “/home/nemo/“ (if you need to find the user’s home directory, get the environment variable $HOME instead) and hardcoding the default values for the XDG data directories without looking up the environment variables ($XDG_DATA_HOME, $XDG_CONFIG_HOME, $XDG_CACHE_HOME) instead. Also no-no: Not using $APPNAME (harbour-myapp) as subdirectory of those XDG dirs. If $XDG_*_HOME is not set (and only then), fall back to the default paths as specified by XDG (e.g. $HOME/.config/ for $XDG_CONFIG_HOME, etc..). Or just use QStandardPaths, which will do The Right Thing(tm).

If we can fix the offline storage path to be correct everytime, we’ll probably introduce these changes into libsailfishapp, so that application developers don’t have to worry about manually setting this all the time (and you can still override this if you want, but you should not [need to]).


HTH :)
Thomas