Add support for Django 3.1

polymorphic/query.py

@@ -6,7 +6,7 @@ import copy
 from collections import defaultdict
 
 from django.contrib.contenttypes.models import ContentType
-from django.db.models import FieldDoesNotExist
+from django.core.exceptions import FieldDoesNotExist
 from django.db.models.query import ModelIterable, Q, QuerySet
 
 from . import compat

polymorphic/query_translate.py

@@ -7,7 +7,7 @@ from collections import deque
 
 from django.apps import apps
 from django.contrib.contenttypes.models import ContentType
-from django.core.exceptions import FieldError
+from django.core.exceptions import FieldError, FieldDoesNotExist
 from django.db import models
 from django.db.models import Q
 from django.db.models.fields.related import ForeignObjectRel, RelatedField
@@ -187,7 +187,7 @@ def translate_polymorphic_field_path(queryset_model, field_path):
                 # Can also test whether the field exists in the related object to avoid ambiguity between
                 # class names and field names, but that never happens when your class names are in CamelCase.
                 return field_path  # No exception raised, field does exist.
-        except models.FieldDoesNotExist:
+        except FieldDoesNotExist:
             pass
 
         submodels = _get_all_sub_models(queryset_model)