From 49ef21d9ea3070aba863af83b22d1ff6dba69f45 Mon Sep 17 00:00:00 2001
From: Karen Tracey <kmtracey@gmail.com>
Date: Tue, 21 Oct 2008 14:04:24 +0000
Subject: [PATCH] Fixed #9039 -- Don't perform unique checks on NULL values,
 since NULL != NULL in SQL.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9239 bcc190cf-cafb-0310-a4f2-bffc1f526a37
---
 django/forms/models.py                 | 21 +++++++--------
 tests/modeltests/model_forms/models.py | 36 +++++++++++++++++++++++++-
 2 files changed, 44 insertions(+), 13 deletions(-)

diff --git a/django/forms/models.py b/django/forms/models.py
index acfa9cec3e..180aec60db 100644
--- a/django/forms/models.py
+++ b/django/forms/models.py
@@ -216,34 +216,31 @@ class BaseModelForm(BaseForm):
     def validate_unique(self):
         from django.db.models.fields import FieldDoesNotExist
 
-        # Gather a list of checks to perform. Since this is a ModelForm, some
-        # fields may have been excluded; we can't perform a unique check on a
-        # form that is missing fields involved in that check.
+        # Gather a list of checks to perform. We only perform unique checks 
+        # for fields present and not None in cleaned_data.  Since this is a 
+        # ModelForm, some fields may have been excluded; we can't perform a unique 
+        # check on a form that is missing fields involved in that check.  It also does
+        # not make sense to check data that didn't validate, and since NULL does not 
+        # equal NULL in SQL we should not do any unique checking for NULL values.
         unique_checks = []
         for check in self.instance._meta.unique_together[:]:
-            fields_on_form = [field for field in check if field in self.fields]
+            fields_on_form = [field for field in check if field in self.cleaned_data and not self.cleaned_data[field] is None]
             if len(fields_on_form) == len(check):
                 unique_checks.append(check)
 
         form_errors = []
 
         # Gather a list of checks for fields declared as unique and add them to
-        # the list of checks. Again, skip fields not on the form.
+        # the list of checks. Again, skip empty fields and any that did not validate.
         for name, field in self.fields.items():
             try:
                 f = self.instance._meta.get_field_by_name(name)[0]
             except FieldDoesNotExist:
                 # This is an extra field that's not on the ModelForm, ignore it
                 continue
-            # MySQL can't handle ... WHERE pk IS NULL, so make sure we
-            # don't generate queries of that form.
-            is_null_pk = f.primary_key and self.cleaned_data[name] is None
-            if name in self.cleaned_data and f.unique and not is_null_pk:
+            if f.unique and name in self.cleaned_data and not self.cleaned_data[name] is None:
                 unique_checks.append((name,))
 
-        # Don't run unique checks on fields that already have an error.
-        unique_checks = [check for check in unique_checks if not [x in self._errors for x in check if x in self._errors]]
-
         bad_fields = set()
         for unique_check in unique_checks:
             # Try to look up an existing object with the same values as this
diff --git a/tests/modeltests/model_forms/models.py b/tests/modeltests/model_forms/models.py
index 0b99a84cda..96b92a3233 100644
--- a/tests/modeltests/model_forms/models.py
+++ b/tests/modeltests/model_forms/models.py
@@ -145,7 +145,15 @@ class Inventory(models.Model):
 
    def __unicode__(self):
       return self.name
-      
+
+class Book(models.Model):
+    title = models.CharField(max_length=40)
+    author = models.ForeignKey(Writer, blank=True, null=True)
+    special_id = models.IntegerField(blank=True, null=True, unique=True)
+    
+    class Meta:
+        unique_together = ('title', 'author')
+
 __test__ = {'API_TESTS': """
 >>> from django import forms
 >>> from django.forms.models import ModelForm, model_to_dict
@@ -1201,6 +1209,32 @@ False
 >>> form.is_valid()
 True
 
+# Unique & unique together with null values
+>>> class BookForm(ModelForm): 
+...     class Meta: 
+...        model = Book
+>>> w = Writer.objects.get(name='Mike Royko')
+>>> form = BookForm({'title': 'I May Be Wrong But I Doubt It', 'author' : w.pk})
+>>> form.is_valid()
+True
+>>> form.save()
+<Book: Book object>
+>>> form = BookForm({'title': 'I May Be Wrong But I Doubt It', 'author' : w.pk})
+>>> form.is_valid()
+False
+>>> form._errors
+{'__all__': [u'Book with this Title and Author already exists.']}
+>>> form = BookForm({'title': 'I May Be Wrong But I Doubt It'})
+>>> form.is_valid()
+True
+>>> form.save()
+<Book: Book object>
+>>> form = BookForm({'title': 'I May Be Wrong But I Doubt It'})
+>>> form.is_valid()
+True
+>>> form.save()
+<Book: Book object>
+
 # Choices on CharField and IntegerField
 >>> class ArticleForm(ModelForm):
 ...     class Meta: