[PyQt] PyQt 5.7, QSqlQueryModel.data() sub-classed override bug?
jnbarchan at gmail.com
Thu May 3 13:55:12 BST 2018
On 3 May 2018 at 13:05, Phil Thompson <phil at riverbankcomputing.com> wrote:
> On 3 May 2018, at 12:25 pm, J Barchan <jnbarchan at gmail.com> wrote:
> > 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 #
> 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) ->
> > 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
> > QVariant QSqlQueryModel::data(const QModelIndex &item, int role =
> Qt::DisplayRole) const
> > Note 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.
> What is QtSql.py?
> If you want to know the signature of a method pss it to help().
> > 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?
> No and no.
> > 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!
Hmm, I had not realised. I use PyCharm as my IDE. From there, while I
am coding, I can click on anything PyQt and ask for "Go to
definition/declaration". The editor then 9in this case) opens me up into a
file named QtSql.py, showing me in this case [extract]:
> def columnCount(self, parent=None, *args, **kwargs): # real signature unknown; NOTE: unreliably restored from __doc__
> """ columnCount(self, parent: QModelIndex = QModelIndex()) -> int """
> def data(self, QModelIndex, role=None): # real signature unknown; restored from __doc__
> """ data(self, QModelIndex, role: int = Qt.DisplayRole) -> Any """
> def endInsertColumns(self): # real signature unknown; restored from __doc__
> """ endInsertColumns(self) """
etc. I had *assumed* this was a file supplied with PyQt. I guess now it's
"generated on the fly" by PyCharm (I see its path is in a PyCharm temporary
directory). At other times, it might open, say,
/usr/lib/python3/dist-packages/PyQt5/QtCore.pyi, which I think is a file
you supply. Oh, at the head of this QtSql.py I see:
# encoding: utf-8
# module PyQt5.QtSql
# from /usr/lib/python3/dist-packages/PyQt5/QtSql.cpython-35m-x86_64-linux-gnu.so
# by generator 1.145
# no doc
You'll probably understand all this better than I!
For my problem:
I think I now understand better why it's not a PyQt method definition issue.
However, from the linked Qt forum discussion, I'm stuck between a rock & a
hard place, because the only help I'm getting is that it might be a PyQt
issue. I do not have C++ to try that out. So, I wonder if I might ask you
if you can make any suggestion as to the cause, even if it is not a PyQt
issue, given that you are familiar with Qt at least?
To summarise my problem as briefly as possible:
I start with:
model = QtSql.QSqlQueryModel(self)
model.setQuery("SELECT LandlordNo, SMTPAccountId FROM landlords WHERE
SMTPAccountId IS NULL")
# or plain "SELECT NULL AS SMTPAccountId", to eliminate anything about
the column definition being an issue
rowCount = model.rowCount()
if rowCount > 0:
rec = model.record(0)
field = rec.field("SMTPAccountId")
isn = field.isNull()
SMTPAccointId returns NULL from MySQL. *At this point field.isNull()
correctly returns True.*
I sub-class QSqlQueryModel, and use that, with quite simply, exactly:
def __init__(self, parent=None):
and use that sub-class in place of QSqlQueryModel: model = DBQueryModel(
*And it this point point field.isNull() *still* correctly returns True.*
Then I add *just exactly this* to my sub-class:
def data(self, index: QtCore.QModelIndex, role=QtCore.Qt.DisplayRole)
return super().data(index, role)
(I've also tried role=None) You can see that simply calls the base class
method. *But now field.isNull() returns False!!* The application sees 0
instead of NULL for the value (SMTPAccountId is declared INT NULL), or ''
if I use SELECT NULL AS SMTPAccountId so it counts as string.
This leaves me completely stumped. I have no idea where the problem is
(there shouldn't be a problem!). I have to sub-class the data() method for
other purposes, but then it handles NULL (only) incorrectly.
Would you have any idea what is going on here? My thanks in advance.
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the PyQt