Fixed #26515 -- Fixed Query.trim_joins() for nested ForeignObjects.

tests/foreign_object/models/customers.py

@@ -0,0 +1,38 @@
+from django.db import models
+from django.db.models.fields.related import ForeignObject
+
+
+class Address(models.Model):
+    company = models.CharField(max_length=1)
+    customer_id = models.IntegerField()
+
+    class Meta:
+        unique_together = [
+            ('company', 'customer_id'),
+        ]
+
+
+class Customer(models.Model):
+    company = models.CharField(max_length=1)
+    customer_id = models.IntegerField()
+    address = ForeignObject(
+        Address, models.CASCADE, null=True,
+        # order mismatches the Contact ForeignObject.
+        from_fields=['company', 'customer_id'],
+        to_fields=['company', 'customer_id'],
+    )
+
+    class Meta:
+        unique_together = [
+            ('company', 'customer_id'),
+        ]
+
+
+class Contact(models.Model):
+    company_code = models.CharField(max_length=1)
+    customer_code = models.IntegerField()
+    customer = ForeignObject(
+        Customer, models.CASCADE, related_name='contacts',
+        to_fields=['customer_id', 'company'],
+        from_fields=['customer_code', 'company_code'],
+    )