fix(apis_entities): only list possible properties in filterset form

The filter `related_properties` listed all the existing properties, but
it makes more sense to only list the properties that can have the model
the filter filters as a `subj` or an `obj`.

Closes: #949

apis_core/apis_entities/filtersets.py

@@ -1,8 +1,10 @@
 import django_filters
 from django.db import models
+from django.db.models import Q
 from apis_core.generic.filtersets import GenericFilterSet, GenericFilterSetForm
 from apis_core.apis_relations.models import Property
 from apis_core.generic.helpers import generate_search_filter
+from django.contrib.contenttypes.models import ContentType
 
 ABSTRACT_ENTITY_FILTERS_EXCLUDE = [
     "rootobject_ptr",
@@ -22,10 +24,31 @@
 ]
 
 
-def related_property(queryset, name, value):
-    p = Property.objects.get(name_forward=value)
-    queryset = queryset.filter(triple_set_from_subj__prop=p).distinct()
-    return queryset
+class PropertyFilter(django_filters.ModelChoiceFilter):
+    """
+    A child of ModelChoiceFilter that only works with
+    Properties, but in return it filters those so that
+    only the Properties are listed that can be connected
+    to the `model` given as argument.
+    """
+
+    def __init__(self, *args, **kwargs):
+        model = kwargs.pop("model", None)
+        super().__init__(*args, **kwargs)
+
+        if model is not None:
+            ct = ContentType.objects.get_for_model(model)
+            self.queryset = (
+                Property.objects.all()
+                .order_by("name_forward")
+                .filter(Q(subj_class=ct) | Q(obj_class=ct))
+                .distinct()
+            )
+
+    def filter(queryset, name, value):
+        p = Property.objects.get(name_forward=value)
+        queryset = queryset.filter(triple_set_from_subj__prop=p).distinct()
+        return queryset
 
 
 def related_entity(queryset, name, value):
@@ -41,11 +64,6 @@ class AbstractEntityFilterSet(GenericFilterSet):
     related_entity = django_filters.CharFilter(
         method=related_entity, label="Related entity contains"
     )
-    related_property = django_filters.ModelChoiceFilter(
-        queryset=Property.objects.all().order_by("name_forward"),
-        label="Related Property",
-        method=related_property,
-    )
 
     class Meta(GenericFilterSet.Meta):
         form = AbstractEntityFilterSetForm
@@ -58,3 +76,9 @@ class Meta(GenericFilterSet.Meta):
                 },
             },
         }
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.filters["related_property"] = PropertyFilter(
+            label="Related Property", model=getattr(self.Meta, "model", None)
+        )