[PyQt] PyQt 5.7, QSqlQueryModel.data() sub-classed override bug?

[J Barchan]

​​
I am finding (in PyQt 5.7 at least) that sub-classing QSqlQueryModel and
overriding its data() method produces an incorrect result when the value
retrieved from a MySQL database is NULL.​

Full details are in
https://forum.qt.io/topic/90363/inexplicable-qsqlquerymodel-handling-of-null-value,
and particularly post #
https://forum.qt.io/topic/90363/inexplicable-qsqlquerymodel-handling-of-null-value.
Nobody has tried it in C++ for me to date to verify, but I'm suspecting
this might be a PyQt bug?

Briefly:
My SELECT query returns a column which is NULLable, and has NULL as its
value.  Where I expect "blank" as the end value, I actually get, for
example, 0 if the column type is *int* or '' if the type is *string*, etc.

This is when I sub-class QSqlQueryModel.  If all I have is:

class DBQueryModel(QtSql.QSqlQueryModel):
    def __init__(self, parent=None):
        super().__init__(parent)

I get the "NULL"/"blank".  However, as soon as I add just:

def data(self, index: QtCore.QModelIndex, role=QtCore.Qt.DisplayRole)
-> typing.Any:
    return super().data(index, role)

I get those values instead of NULL.

Note that my override is based on the Qt definition of the method at
http://doc.qt.io/qt-5/qsqlquerymodel.html#data:
QVariant <http://doc.qt.io/qt-5/qvariant.html> QSqlQueryModel::data(const
QModelIndex <http://doc.qt.io/qt-5/qmodelindex.html> &*item*, int *role* =
Qt::DisplayRole) constNote that the default for role is Qt::DisplayRole.
However, in QtSql.py I see:

def data(self, QModelIndex, role=None): # real signature unknown;
restored from __doc__
    """ data(self, QModelIndex, role: int = Qt.DisplayRole) -> Any """
    pass

 You will notice that the *comment* shows the default should be
Qt.DisplayRole, but the declaration defaults it to None instead.

I don't know enough to be sure, but would that be the underlying cause of
the unexpected behaviour?

FWIW, I have tried making my override be:

def data(self, index: QtCore.QModelIndex, role=None)

instead, but same bad behaviour.

1. Is this indeed a bug in PyQt, and the cause of my issue?
2. If so, I presume you (Phil!) will be kind enough to fix.  However, for
my part I am stuck with PyQt 5.7 for the foreseeable future.  If the fix is
indeed to change code in the latest/next release, is there anything I can
do in existing code (my override) to make it work in 5.7, as a workaround?
(in real code I need the override, as I do other processing)

My coding has come to halt as I cannot proceed without a fix.  So I should
be obliged for any early response as to whether this is the cause of my
woes.  I do realise PyQt support/fixes are quite voluntary, and so thank
whoever in advance!


-- 
Kindest,
Jonathan
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