Polymorphic Filtering (for fields in inherited classes) enhance

[bgrantdev]

Sorry in advance I wanted to label this an enhancement but the labels aren't showing up.

`class Project(PolymorphicModel):
topic = models.CharField(max_length=30)

class ArtProject(Project):
artist = models.CharField(max_length=30)

class ResearchProject(Project):
supervisor = models.CharField(max_length=30)

class ScienceProject(Project):
supervisor = models.CharField(max_length=30)
other_field = models.BooleanField()`

I may have missed this in the documentation but if two inherited models share a common field in this case the supervisor field shared by the Research and Science project is there a cleaner way to make a query on supervisor other than.

results = Project.objects.filter(Q(ResearchProject___supervisor="Bob") | Q(ScienceProject___supervisor="Bob"))

something like

results = Project.objects.instance_of(ResearchProject, ScienceProject).filter(supervisor="Bob")

or even better would be

results = Project.objects.filter(supervisor="Bob")

[vdboor]

That's an interesting idea. However I'm not sure if the instance_of(..) is easy to understand; there is a magic in the chaining that makes .filter(supervisor=..) either work or not. The last example would be wonderful, I'm not sure yet how easy it will be to realize.

[DDevine]

I have come across this issue too. I do not want to have to manually create Q objects all throughout my code every time I add a new child to polymorphic class.

Instead of the following code to check if a device is in a user's domain for all the different device types:

domains = Domain.objects.filter(groups__in=user.groups.all())
devices = Device.objects.all()
return devices.filter(domains__in=domains)

I have to do the following when I add the DMXDevice class a new type of device, of potentially half a dozen to be added over the next year, and potentially by people other than myself...

domains = Domain.objects.filter(groups__in=user.groups.all())
devices = Q(DALIDevice.objects.all()) | Q(DMXDevice.objects.all()) 
return devices.filter(domains__in=domains)

I had a look into writing a fix by basically splitting the queryset into Q objects before filtering in the filter() method of PolymorphicQuerySet, but it appears that this has already been done (in the function that filter() uses) as you can see here: https://github.com/django-polymorphic/django-polymorphic/blob/f9fffc44c12ebb524ddf002e6fd5f9d221f36f7a/polymorphic/query.py#L113

Why does it throw exceptions when it tries to access an attribute that does not exist on the parent object ('domains' in my case)? How can this be worked around?