2008-04-16 Qt database widgets

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I've been playing with a couple of Qt classes to get an easy-to-use SQL user interface. The combo QTableView and QSqlTableModel seemed very nice. Using the Designer, I could click an interface together and voilĂ , a nice grid where the user can edit the database.

There were a couple of hicks. If fields were NULL in the database, these could be filled in but never put back to NULL. After reading and trying out lots of stuff, I found the following classes are involved:

QTableView Provides the general table widget on the screen
QItemDelegate Provides view/edit functions for specific cell types in the table widget on the screen
QSqlTableModel This class provides an easy-to-use API for a database table
QAbstractProxyModel A class that can be stuck over QSqlTableModel to transform, sort or filter data when it comes in or goes out of the QSqlTableModel

You have to think about what functions exactly you want to change. If it's the overall interface, think about the QTableView. In my case, I wanted to enable the user to set fields to NULL. The normal QItemDelegate doesn't allow this.

In the end I avoided the whole issue by using one type field (which can contain 'string', 'integer', 'double' et cetera.