Still generate uniqueness lookups when a uniqueness field is empty.

In our specific example, we have Sections, with uniqueness on the tuple
of (parent, instance). parent is optional and can be None, but we still
want uniqueness of the tuple when that is the case.

sluggable/tests/models.py

@@ -42,3 +42,9 @@ class DayPost(models.Model):
     date = models.DateField()
     slug = SluggableField(unique_with='date')
     slugs = generic.GenericRelation(PostSlug)
+
+class WordPost(models.Model):
+    user = models.ForeignKey(User)
+    word = models.CharField(max_length=50, blank=True)
+    slug = SluggableField(unique_with=('user', 'word'))
+    slugs = generic.GenericRelation(PostSlug)

sluggable/tests/tests.py

@@ -4,7 +4,7 @@
 
 from django.test import TestCase
 
-from .models import Poll, PollSlug, UserSlug, User, Post, DayPost, PostSlug
+from .models import Poll, PollSlug, UserSlug, User, Post, DayPost, WordPost, PostSlug
 
 
 class SluggableTests(TestCase):
@@ -174,3 +174,18 @@ def test_unique_with(self):
 
     def test_unique_with_date(self):
         self._unique_with(DayPost, 'date', date(2014, 1, 1), date(2014, 2, 1))
+
+    def test_unique_with_blank_word(self):
+        user = User.objects.create(username='matthew')
+
+        post1 = WordPost.objects.create(user=user, word='word', slug='a-slug')
+        post2 = WordPost.objects.create(user=user, word='word', slug='a-slug')
+        post3 = WordPost.objects.create(user=user, word='', slug='a-slug')
+        post4 = WordPost.objects.create(user=user, word='', slug='a-slug')
+
+        self.assertEquals(PostSlug.objects.count(), 4)
+
+        self.assertEquals(post1.slug, 'a-slug')
+        self.assertEquals(post2.slug, 'a-slug-2')
+        self.assertEquals(post3.slug, 'a-slug')
+        self.assertEquals(post4.slug, 'a-slug-2')

sluggable/utils.py

@@ -100,9 +100,7 @@ def get_uniqueness_lookups(field, instance, unique_with):
                              % (instance._meta.object_name, field_name))
 
         value = getattr(instance, field_name)
-        if not value:
-            if other_field.blank:
-                break
+        if not value and not other_field.blank:
             raise ValueError('Could not check uniqueness of %s.%s with'
                              ' respect to %s.%s because the latter is empty.'
                              ' Please ensure that "%s" is declared *after*'