On Thursday, 4 June 2020 16:25:09 UTC+1, OwlHoot wrote:
>
>
> I believe the issue I have enquired about on the following Stack Exchange
> page :
>
>
> https://stackoverflow.com/questions/62162288/baffling-error-filtering-django-objects-of-derived-class-by-values-in-foreign-ke
>
By adding some debug code in
/usr/lib/python3.6/site-packages/django/db/backends/base/creation.py I have
made some progress with this "bug" (which I am no longer convinced it is).
The issue relates to a load of derived classes, as follows :
class DataSet(models.Model)
class PSessionDataSet(DataSet)
:::
class FilteredDataSet(DataSet)
class AggregateDataSet(DataSet)
class SurveyRunDataSet(DataSet)
class RestrictedDataSet(SurveyRunDataSet)
These all have the same app_label value ("dataset") in their Meta class,
and are thus in the same "group" of models.
However, the debug logging line reveals that Django thinks all these
classes share the same default manager (_default_manager), namely
dataset.AggregateDataSet.objects:
Model
Default Manager
:::
app.survey.models.grid.GridRow
survey.GridRow.objects
app.analysis.models.Analysis
analysis.Analysis.objects
app.analysis.report.models.AnalysisReport
report.AnalysisReport.objects
app.analysis.dataset.models.dataset.DataSet
dataset.AggregateDataSet.objects
app.analysis.dataset.models.survey_run.SurveyRunDataSet
dataset.AggregateDataSet.objects
app.analysis.dataset.models.filtered.FilteredDataSet
dataset.AggregateDataSet.objects
app.analysis.dataset.models.restricted.RestrictedDataSet
dataset.AggregateDataSet.objects
Now I know the documentation says the default manager is chosen as the
first it happens to come across in the model group. But that sounds
absolutely barking mad. Shouldn't each of these models have their own
model-specific default manager, as all the models preceding the "dataset"
models do in the above table?!
Otherwise surely the manager will have trouble finding various
columns/values in a model table other than the one on which it is based,
which is exactly the error I am seeing!
So now my problem becomes how to tweak each of these "dataset" models so
their default managers will become as follows :
Model
Default Manager
:::
app.survey.models.grid.GridRow
survey.GridRow.objects
app.analysis.models.Analysis
analysis.Analysis.objects
app.analysis.report.models.AnalysisReport
report.AnalysisReport.objects
app.analysis.dataset.models.dataset.DataSet
dataset.DataSet.objects
app.analysis.dataset.models.survey_run.SurveyRunDataSet
dataset.SurveyRunDataSet.objects
app.analysis.dataset.models.filtered.FilteredDataSet
dataset.FilteredDataSet.objects
app.analysis.dataset.models.restricted.RestrictedDataSet
dataset.RestrictedDataSet.objects
Would that just be a matter of adding lines as follows (typically in the
FilteredDataSet class) :
objects = FilteredDataSet.Manager()
or does one need a more elaborate overriding of get_queryset() ?
Any ideas gratefully received.
?
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