Good way to multiple access SQL

[cfdev]

Hi,
Sorry if my question is too simple but I ask me what is the good way to multiple access SQL.

My Qt software:
1- Load data in class and display in widget
2- User can changes data and Update SQL through the class.
Ok simple!

But in multiple access case:
1- USER 1 Load data in class and display in widget
2- USER 2 Load data in class and display in widget
3- USER 1 makes some data changes and Update SQL through the class.
4- USER 2 makes some data changes and Update SQL through the class.
-> Error: the changements of USER 1 are erased by USER 2 without message or other.

How to do this ? Thanks

[cfdev]

In the case of SQLITE or MYSQL ?

[VRonin]

If all users access the database only through your application you can have them notify one another of changes via QTcpSocket otherwise before submitting any change you need to perform a select and check that the value was not altered in the meantime

[mjsurette]

Check out QSqlDriver's notification capability. From personal experience it works well with Postgresql. I would assume that it works with MySQL, perhaps even SQLite. It is dependent on the driver implementation though.

Mike

[VRonin]

check hasFeature() but I doubt SQLite has QSqlDriver::EventNotifications

[cfdev]

qDebug() << "driver EventNotifications: " << sdlDrv->hasFeature(QSqlDriver::EventNotifications);

-> driver EventNotifications: false

Arf, so I must make it manually ? by QTcpSocket or internally by an flag ?

[VRonin]

I'm afraid so

[kshegunov]

Use the original data as a where clause for the update statement. This way if the data has changed in the meantime you can know, and show a message to the user, even suggest him a reload.

[cfdev]

@kshegunov This, complicates the SQL requests...

[kshegunov]

@cfdev
That may be, but guarantees consistency! In any case there isn't another reliable way to do it, beside writing your own application server.

[cfdev]

Ok, many thanks at All!