Fix retrieving model for reverse relations

Author: glowka

.idea/drf-yasg.iml

@@ -1,5 +1,6 @@
 import datetime
 import inspect
+import itertools
 import logging
 import operator
 import sys
@@ -223,15 +224,23 @@ def get_related_model(model, source):
     :param str source: related field name
     :return: related model or ``None``
     """
+    descriptor = model
     try:
-        descriptor = getattr(model, source)
-        try:
-            return descriptor.rel.related_model
-        except Exception:
-            return descriptor.field.remote_field.model
-    except Exception:  # pragma: no cover
+        for attr in source.split('.'):
+            descriptor = getattr(descriptor, attr)
+    except AttributeError:  # pragma: no cover
         return None
 
+    try:
+        is_forward = descriptor.field in itertools.chain(model._meta.fields, model._meta.many_to_many)
+    except AttributeError:  # pragma: no cover
+        return None
+
+    if is_forward:
+        return descriptor.field.related_model
+    else:
+        return descriptor.field.model
+
 
 class RelatedFieldInspector(FieldInspector):
     """Provides conversions for ``RelatedField``\\ s."""

.idea/misc.xml

@@ -7,11 +7,11 @@
 from django.contrib.postgres import fields as postgres_fields
 from django.db import models
 from django.utils.inspect import get_func_args
-from django_fake_model import models as fake_models
 from rest_framework import routers, serializers, viewsets
 from rest_framework.decorators import api_view
 from rest_framework.response import Response
 
+from django_fake_model import models as fake_models
 from drf_yasg import codecs, openapi
 from drf_yasg.codecs import yaml_sane_load
 from drf_yasg.errors import SwaggerGenerationError

src/drf_yasg/inspectors/field.py

@@ -55,6 +55,7 @@ skip_install = true
 deps =
     -r requirements/lint.txt
 commands =
+    isort --recursive src tests
     flake8 src/drf_yasg testproj tests setup.py
 
 [testenv:docs]