improve follow_field_source for reverse resolution and model leafs #150

drf_spectacular/plumbing.py

@@ -12,8 +12,8 @@
 
 import inflection
 import uritemplate
-from django import __version__ as DJANGO_VERSION
 from django.apps import apps
+from django.db.models.fields.reverse_related import ForeignObjectRel
 from django.urls.resolvers import (  # type: ignore
     _PATH_PARAMETER_COMPONENT_RE, RegexPattern, Resolver404, RoutePattern, URLPattern, URLResolver,
     get_resolver,
@@ -341,19 +341,11 @@ def append_meta(schema, meta):
     return safe_ref({**schema, **meta})
 
 
-def get_field_from_model(model, field):
+def _follow_field_source(model, path: List[str]):
     """
-    this is a Django 2.2 compatibility function to access a field through a Deferred Attribute
+        navigate through root model via given navigation path. supports forward/reverse relations.
     """
-    if DJANGO_VERSION.startswith('2'):
-        # field.field will in effect return self, i.e. a DeferredAttribute again (loop)
-        return model._meta.get_field(field.field_name)
-    else:
-        return field.field
-
-
-def _follow_field_source(model, path):
-    field_or_property = getattr(model, path[0])
+    field_or_property = getattr(model, path[0], None)
 
     if len(path) == 1:
         # end of traversal
@@ -362,7 +354,12 @@ def _follow_field_source(model, path):
         elif callable(field_or_property):
             return field_or_property
         else:
-            return get_field_from_model(model, field_or_property)
+            field = model._meta.get_field(path[0])
+            if isinstance(field, ForeignObjectRel):
+                # resolve DRF internal object to PK field as approximation
+                return field.get_related_field()  # type: ignore
+            else:
+                return field
     else:
         if isinstance(field_or_property, property) or callable(field_or_property):
             if isinstance(field_or_property, property):
@@ -377,7 +374,7 @@ def _follow_field_source(model, path):
                 )
             return _follow_field_source(target_model, path[1:])
         else:
-            target_model = field_or_property.field.related_model
+            target_model = model._meta.get_field(path[0]).related_model
             return _follow_field_source(target_model, path[1:])
 
 

tests/test_plumbing.py

@@ -1,7 +1,8 @@
 from django.db import models
 from rest_framework import serializers
 
-from drf_spectacular.plumbing import force_instance, is_field, is_serializer
+from drf_spectacular.openapi import AutoSchema
+from drf_spectacular.plumbing import follow_field_source, force_instance, is_field, is_serializer
 
 
 def test_is_serializer():
@@ -30,3 +31,31 @@ def test_force_instance():
     assert isinstance(force_instance(serializers.CharField), serializers.CharField)
     assert force_instance(5) == 5
     assert force_instance(dict) == dict
+
+
+def test_follow_field_source_forward_reverse(no_warnings):
+    class FFS1(models.Model):
+        field_bool = models.BooleanField()
+
+    class FFS2(models.Model):
+        ffs1 = models.ForeignKey(FFS1, on_delete=models.PROTECT)
+
+    class FFS3(models.Model):
+        ffs2 = models.ForeignKey(FFS2, on_delete=models.PROTECT)
+        field_float = models.FloatField()
+
+    forward_field = follow_field_source(FFS3, ['ffs2', 'ffs1', 'field_bool'])
+    reverse_field = follow_field_source(FFS1, ['ffs2', 'ffs3', 'field_float'])
+    forward_model = follow_field_source(FFS3, ['ffs2', 'ffs1'])
+    reverse_model = follow_field_source(FFS1, ['ffs2', 'ffs3'])
+
+    assert isinstance(forward_field, models.BooleanField)
+    assert isinstance(reverse_field, models.FloatField)
+    assert isinstance(forward_model, models.ForeignKey)
+    assert isinstance(reverse_model, models.AutoField)
+
+    auto_schema = AutoSchema()
+    assert auto_schema._map_model_field(forward_field, None)['type'] == 'boolean'
+    assert auto_schema._map_model_field(reverse_field, None)['type'] == 'number'
+    assert auto_schema._map_model_field(forward_model, None)['type'] == 'integer'
+    assert auto_schema._map_model_field(reverse_model, None)['type'] == 'integer'