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I have a model linked to a related model that is a Django MPTT tree model, I would like to be able to filter the first model using the Django MPTT tree in the admin console.

class Tenders(models.Model):
 ...
 sector=models.ForeignKey(Sector, to_field='sectorId', null=True, blank=True,on_delete=models.CASCADE)
 ...

class Sector(MPTTModel):
 name = models.CharField(max_length = 255)
 parent = TreeForeignKey('self', on_delete=models.CASCADE, null=True, blank=True,related_name='children')
 sectorId = models.IntegerField(default=0,null=True,unique=True)

In the Django admin I would like to set up the filters for the Tenders model such that the Django-MPTT tree is the filter.

I have tried using the following:

class adminTenders(admin.ModelAdmin): 
 def linkTo(self,obj):
 return mark_safe("""<a href='' target="_blank" >Tender Link</a>""".format(obj.tenderLink))
 linkTo.short_description=''

 list_display=(
 'title',
 'linkTo',
 'sector',
 'region',
 'repository',
 'id',
 )
 list_filter=(
 ('sector', TreeRelatedFieldListFilter),
 )

admin.site.register(Tenders,adminTenders)

However I get the following error when trying to run this and I cant figure it out:

 File "py36/lib/python3.6/site-packages/mptt/admin.py", line 314, in field_choices
 mptt_level_indent * levels_dict[pk])
 KeyError: 0

Any help would be greatly appreciated.

Edit 1: I think I have isolated the issue to the fact that my foreign key in Tenders to Sectors uses a to_field='sectorId instead of the default to link to the pk column. This had to be done for backwards compatibility to an old database scheme that I am stuck with.

So it turns out this is a bug in the django-mptt code for the field_choices function in the TreeRelatedFieldListFilter class.

To fix it I had to subclass and over ride that function to use the to_field that I had defined.

Here is the custom code:

class TreeRelatedForSectors(TreeRelatedFieldListFilter):
 # Modified from django-mptt code to fix to_field problem
 def field_choices(self, field, request, model_admin):
 mptt_level_indent = getattr(model_admin, 'mptt_level_indent', self.mptt_level_indent)
 language_bidi = get_language_bidi()
 initial_choices = field.get_choices(include_blank=False)
 pks = [pk for pk, val in initial_choices]
 models = field.related_model._default_manager.filter(sectorId__in=pks)
 levels_dict = model.sectorId: getattr(model, model._mptt_meta.level_attr) for model in models
 choices = []
 for pk, val in initial_choices:
 padding_style = ' style="padding-%s:%spx"' % (
 'right' if language_bidi else 'left',
 mptt_level_indent * levels_dict[pk])
 choices.append((pk, val, mark_safe(padding_style)))
 return choices