[1.7.x] Fixed #23455 -- Forced related_name to be a unicode string during deconstruction.

Backport of 45bd7b3bd9 from master

django/db/models/fields/related.py

@@ -14,7 +14,7 @@ from django.db.models.lookups import IsNull
 from django.db.models.related import RelatedObject, PathInfo
 from django.db.models.query import QuerySet
 from django.db.models.sql.datastructures import Col
-from django.utils.encoding import smart_text
+from django.utils.encoding import force_text, smart_text
 from django.utils import six
 from django.utils.deprecation import RenameMethodsBase, RemovedInDjango18Warning
 from django.utils.translation import ugettext_lazy as _
@@ -1363,7 +1363,7 @@ class ForeignObject(RelatedField):
         kwargs['from_fields'] = self.from_fields
         kwargs['to_fields'] = self.to_fields
         if self.rel.related_name is not None:
-            kwargs['related_name'] = self.rel.related_name
+            kwargs['related_name'] = force_text(self.rel.related_name)
         if self.rel.related_query_name is not None:
             kwargs['related_query_name'] = self.rel.related_query_name
         if self.rel.on_delete != CASCADE:
@@ -2099,7 +2099,7 @@ class ManyToManyField(RelatedField):
         if self.rel.db_constraint is not True:
             kwargs['db_constraint'] = self.rel.db_constraint
         if self.rel.related_name is not None:
-            kwargs['related_name'] = self.rel.related_name
+            kwargs['related_name'] = force_text(self.rel.related_name)
         if self.rel.related_query_name is not None:
             kwargs['related_query_name'] = self.rel.related_query_name
         # Rel needs more work.

docs/releases/1.7.1.txt

@@ -76,3 +76,7 @@ Bugfixes
 
 * Added ``SchemaEditor`` for MySQL GIS backend so that spatial indexes will be
   created for apps with migrations (:ticket:`23538`).
+
+* Coerced the ``related_name`` model field option to unicode during migration
+  generation to generate migrations that work with both Python 2 and 3
+  (:ticket:`23455`).

tests/field_deconstruction/tests.py

@@ -1,3 +1,5 @@
+from __future__ import unicode_literals
+
 import warnings
 
 from django.db import models
@@ -209,6 +211,12 @@ class FieldDeconstructionTests(TestCase):
         self.assertEqual(path, "django.db.models.ForeignKey")
         self.assertEqual(args, [])
         self.assertEqual(kwargs, {"to": "auth.Permission", "related_name": "foobar"})
+        # Test related_name unicode conversion
+        field = models.ForeignKey("auth.Permission", related_name=b"foobar")
+        name, path, args, kwargs = field.deconstruct()
+        self.assertEqual(path, "django.db.models.ForeignKey")
+        self.assertEqual(args, [])
+        self.assertEqual(kwargs, {"to": "auth.Permission", "related_name": "foobar"})
 
     @override_settings(AUTH_USER_MODEL="auth.Permission")
     def test_foreign_key_swapped(self):
@@ -289,6 +297,12 @@ class FieldDeconstructionTests(TestCase):
         self.assertEqual(path, "django.db.models.ManyToManyField")
         self.assertEqual(args, [])
         self.assertEqual(kwargs, {"to": "auth.Permission", "related_name": "custom_table"})
+        # Test related_name unicode conversion
+        field = models.ManyToManyField("auth.Permission", related_name=b"custom_table")
+        name, path, args, kwargs = field.deconstruct()
+        self.assertEqual(path, "django.db.models.ManyToManyField")
+        self.assertEqual(args, [])
+        self.assertEqual(kwargs, {"to": "auth.Permission", "related_name": "custom_table"})
 
     @override_settings(AUTH_USER_MODEL="auth.Permission")
     def test_many_to_many_field_swapped(self):