Allow user to define their own display formats. The SQL code is editable
and the combo box changes automatically to custom if the user edits one
of the predefined formats.
The display format (either custom or predefined) is validated with a
case-insensitive regex so at least it contains a function applied to the column
name.
Added a new callback for executeSQL following the model of sqlite3_exec.
Using this, the number of columns is got from a checking query execution. If
it is not one, the custom display format is also rejected.
Note that these validations might still be fooled in some unforeseen way, but
the users should know what they're doing.
See issue #573
This is a proof-of-concept or even a basic first implementation of a new
feature I'd like to have in DB4S which at the moment I call display
formats.
The idea here is to allow the user to change the data in the Browse Data
tab on a per column basis before displaying it. This means even though
the data is stored in format X in the database it can be shown in format
Y in the browser. This should be useful in cases where the original
format X is hard to read or just not useful in a particular case.
This first implementation allows the user to right click on the header
of a column and open a new dialog for setting the display format which
offers a (limited) list of pre-defined formats. The selected format is
then integrated into the SELECT statement which is sent to SQLite.
While it works, this draft implementation lacks a number of features.
Here are the most prominent ones I'm currently aware of:
* Data not editable (or only via the Edit Dialog) because it isn't
transformed back yet.
* More display formats needed; maybe customizable ones, too.
* No indication in the UI for which columns a format has been set.
* Could _maybe_ be integrated into the import/export etc. for optional
use.
