Fixed #24505 -- Fixed clash with hidden m2m fields.

Added support for multiple m2m fields with the same 'to' model
and with related_name set to '+'.

django/db/models/fields/related.py

@@ -2621,6 +2621,12 @@ class ManyToManyField(RelatedField):
         if self.remote_field.symmetrical and (
                 self.remote_field.model == "self" or self.remote_field.model == cls._meta.object_name):
             self.remote_field.related_name = "%s_rel_+" % name
+        elif self.remote_field.is_hidden():
+            # If the backwards relation is disabled, replace the original
+            # related_name with one generated from the m2m field name. Django
+            # still uses backwards relations internally and we need to avoid
+            # clashes between multiple m2m fields with related_name == '+'.
+            self.remote_field.related_name = "_%s_+" % name
 
         super(ManyToManyField, self).contribute_to_class(cls, name, **kwargs)
 

tests/m2m_regress/models.py

@@ -54,9 +54,13 @@ class SelfReferChildSibling(SelfRefer):
 
 
 # Many-to-Many relation between models, where one of the PK's isn't an Autofield
+@python_2_unicode_compatible
 class Line(models.Model):
     name = models.CharField(max_length=100)
 
+    def __str__(self):
+        return self.name
+
 
 class Worksheet(models.Model):
     id = models.CharField(primary_key=True, max_length=100)
@@ -87,3 +91,10 @@ class RegressionModelSplit(BadModelWithSplit):
     Model with a split method should not cause an error in add_lazy_relation
     """
     others = models.ManyToManyField('self')
+
+
+# Regression for #24505 -- Two ManyToManyFields with the same "to" model
+# and related_name set to '+'.
+class Post(models.Model):
+    primary_lines = models.ManyToManyField(Line, related_name='+')
+    secondary_lines = models.ManyToManyField(Line, related_name='+')

tests/m2m_regress/tests.py

@@ -5,7 +5,7 @@ from django.test import TestCase
 from django.utils import six
 
 from .models import (
-    Entry, RegressionModelSplit, SelfRefer, SelfReferChild,
+    Entry, Line, Post, RegressionModelSplit, SelfRefer, SelfReferChild,
     SelfReferChildSibling, Tag, TagCollection, Worksheet,
 )
 
@@ -111,3 +111,14 @@ class M2MRegressionTests(TestCase):
 
         c1.refresh_from_db()
         self.assertQuerysetEqual(c1.tags.order_by('name'), ["<Tag: t1>", "<Tag: t2>"])
+
+    def test_multiple_forwards_only_m2m(self):
+        # Regression for #24505 - Multiple ManyToManyFields to same "to"
+        # model with related_name set to '+'.
+        foo = Line.objects.create(name='foo')
+        bar = Line.objects.create(name='bar')
+        post = Post.objects.create()
+        post.primary_lines.add(foo)
+        post.secondary_lines.add(bar)
+        self.assertQuerysetEqual(post.primary_lines.all(), ['<Line: foo>'])
+        self.assertQuerysetEqual(post.secondary_lines.all(), ['<Line: bar>'])

tests/model_meta/results.py

@@ -319,7 +319,7 @@ TEST_RESULTS = {
     'get_all_related_objects_with_model_hidden_local': {
         Person: (
             ('+', None),
-            ('+', None),
+            ('_people_hidden_+', None),
             ('Person_following_inherited+', None),
             ('Person_following_inherited+', None),
             ('Person_friends_inherited+', None),
@@ -334,7 +334,7 @@ TEST_RESULTS = {
         ),
         BasePerson: (
             ('+', None),
-            ('+', None),
+            ('_basepeople_hidden_+', None),
             ('BasePerson_following_abstract+', None),
             ('BasePerson_following_abstract+', None),
             ('BasePerson_following_base+', None),
@@ -380,10 +380,10 @@ TEST_RESULTS = {
     },
     'get_all_related_objects_with_model_hidden': {
         Person: (
-            ('+', BasePerson),
             ('+', BasePerson),
             ('+', None),
-            ('+', None),
+            ('_basepeople_hidden_+', BasePerson),
+            ('_people_hidden_+', None),
             ('BasePerson_following_abstract+', BasePerson),
             ('BasePerson_following_abstract+', BasePerson),
             ('BasePerson_following_base+', BasePerson),
@@ -416,7 +416,7 @@ TEST_RESULTS = {
         ),
         BasePerson: (
             ('+', None),
-            ('+', None),
+            ('_basepeople_hidden_+', None),
             ('BasePerson_following_abstract+', None),
             ('BasePerson_following_abstract+', None),
             ('BasePerson_following_base+', None),
@@ -730,7 +730,7 @@ TEST_RESULTS = {
             ('friends_base_rel_+', None),
             ('followers_base', None),
             ('relating_basepeople', None),
-            ('+', None),
+            ('_basepeople_hidden_+', None),
         ),
         Person: (
             ('friends_abstract_rel_+', BasePerson),
@@ -738,11 +738,11 @@ TEST_RESULTS = {
             ('friends_base_rel_+', BasePerson),
             ('followers_base', BasePerson),
             ('relating_basepeople', BasePerson),
-            ('+', BasePerson),
+            ('_basepeople_hidden_+', BasePerson),
             ('friends_inherited_rel_+', None),
             ('followers_concrete', None),
             ('relating_people', None),
-            ('+', None),
+            ('_people_hidden_+', None),
         ),
         Relation: (
             ('m2m_abstract_rel', None),
@@ -757,13 +757,13 @@ TEST_RESULTS = {
             'friends_base_rel_+',
             'followers_base',
             'relating_basepeople',
-            '+',
+            '_basepeople_hidden_+',
         ],
         Person: [
             'friends_inherited_rel_+',
             'followers_concrete',
             'relating_people',
-            '+',
+            '_people_hidden_+',
         ],
         Relation: [
             'm2m_abstract_rel',

tests/model_meta/tests.py

@@ -237,7 +237,7 @@ class RelationTreeTests(TestCase):
         self.assertEqual(
             sorted([field.related_query_name() for field in BasePerson._meta._relation_tree]),
             sorted([
-                '+', '+', 'BasePerson_following_abstract+', 'BasePerson_following_abstract+',
+                '+', '_basepeople_hidden_+', 'BasePerson_following_abstract+', 'BasePerson_following_abstract+',
                 'BasePerson_following_base+', 'BasePerson_following_base+', 'BasePerson_friends_abstract+',
                 'BasePerson_friends_abstract+', 'BasePerson_friends_base+', 'BasePerson_friends_base+',
                 'BasePerson_m2m_abstract+', 'BasePerson_m2m_base+', 'Relating_basepeople+',