Fix retrieving model for reverse relations

src/drf_yasg/inspectors/field.py

@@ -1,5 +1,6 @@
 import datetime
 import inspect
+import itertools
 import logging
 import operator
 import typing
@@ -212,15 +213,23 @@ 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."""

testproj/users/migrations/0002_setup_oauth2_apps.py

@@ -1,4 +1,5 @@
 # Generated by Django 2.1.3 on 2018-12-19 07:57
+import pkg_resources
 from django.conf import settings
 from django.db import migrations
 
@@ -27,10 +28,16 @@ def add_oauth_apps(apps, schema_editor):
         Application.objects.get_or_create(client_id=app['client_id'], defaults=app)
 
 
+def get_oauth_dependency():
+    oauth_version = pkg_resources.get_distribution('django-oauth-toolkit').version.split('.')[:2]
+    # 1.1 and 1.2 are before squasing migrations into 0001_initial
+    return '0006_auto_20171214_2232' if oauth_version in (('1', '1'), ('1', '2')) else '0001_initial'
+
+
 class Migration(migrations.Migration):
     dependencies = [
         migrations.swappable_dependency(settings.AUTH_USER_MODEL),
-        ('oauth2_provider', '0002_auto_20190406_1805'),
+        ('oauth2_provider', get_oauth_dependency()),
         ('users', '0001_create_admin_user'),
     ]
 

tests/test_schema_generator.py

@@ -7,11 +7,11 @@
 from django.db import models
 from django.urls import path
 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