ManyToManyField empty when setting related_name and related_query_name to "+"

[Hayder Mustafa]

I’ve encountered an issue in my Django project where using the following configuration in a ManyToManyField causes the field to return an empty queryset—even though the underlying join table contains records. Notably, this bug appears to be intermittent; sometimes the field behaves as expected, while other times it consistently returns an empty queryset.

move_lines = models.ManyToManyField(
    "accounting.AccountMoveLine",
    verbose_name="Move Lines",
    related_name="+",
    related_query_name="+",
    blank=True,
)

Steps to Reproduce:

Define a model with a ManyToManyField that includes related_name="+" and related_query_name="+" (to disable reverse relations).

Create and save related records so that there are entries in the join table.

Query the field using instance.move_lines.all().

Observe that the queryset is empty despite the related records existing. Note that the bug does not occur consistently—there are occasions where the field returns the expected records.

Expected Behavior:
The field should return all associated records when queried, regardless of the reverse relation being disabled.

Actual Behavior:
When related_name and related_query_name are set to "+", instance.move_lines.all() sometimes returns an empty queryset even though related records exist. Removing these attributes (thus allowing Django to generate default reverse names) consistently resolves the issue.

Additional Context:
This appears to be an issue where disabling the reverse relationship by setting the related names to "+" intermittently interferes with the ORM’s ability to construct the proper join, resulting in an empty result set on the forward lookup. Has anyone else experienced this behavior, or is there a known workaround or fix for this issue?

Thanks in advance for any help or insights!

[Sarah Boyce]

I cannot replicate, can you try to write a regression test?

This was what I have tested:

tests/m2m_regress/models.py

@@ -93 +93 @@
 class Post(models.Model):
     primary_lines = models.ManyToManyField(Line, related_name="+")
     secondary_lines = models.ManyToManyField(Line, related_name="+")
+
+
+class Test(models.Model):
+    lines = models.ManyToManyField(Line, related_name="+", related_query_name="+")

tests/m2m_regress/tests.py

@@ -11 +11 @@
     SelfReferChildSibling,
     Tag,
     TagCollection,
+    Test,
     Worksheet,
 )
 
@@ -141 +142 @@
         post.secondary_lines.add(bar)
         self.assertSequenceEqual(post.primary_lines.all(), [foo])
         self.assertSequenceEqual(post.secondary_lines.all(), [bar])
+
+    def test_related_name_and_related_query_name_plus(self):
+        instance = Test.objects.create()
+        foo = Line.objects.create(name="foo")
+        bar = Line.objects.create(name="bar")
+        instance.lines.add(foo)
+        instance.lines.add(bar)
+        self.assertSequenceEqual(instance.lines.all(), [foo, bar])
+        instance.refresh_from_db()
+        self.assertSequenceEqual(instance.lines.all(), [foo, bar])