Fixes #2918 -- Clarified the db_prep_save logic for DateField and Dat…

…eTimeField to prevent accidental conversion of non-datetime objects into strings, because SQLite doesn't appear to check for valid date format in a string used on an UPDATE of a datetime column.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@3960 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/fields/__init__.py

@@ -457,7 +457,9 @@ def get_follow(self, override=None):
 
     def get_db_prep_save(self, value):
         # Casts dates into string format for entry into database.
-        if value is not None:
+        if isinstance(value, datetime.datetime):
+            value = value.date().strftime('%Y-%m-%d')
+        elif isinstance(value, datetime.date):
             value = value.strftime('%Y-%m-%d')
         return Field.get_db_prep_save(self, value)
 
@@ -487,12 +489,19 @@ def to_python(self, value):
 
     def get_db_prep_save(self, value):
         # Casts dates into string format for entry into database.
-        if value is not None:
+        if isinstance(value, datetime.datetime):
             # MySQL will throw a warning if microseconds are given, because it
             # doesn't support microseconds.
             if settings.DATABASE_ENGINE == 'mysql' and hasattr(value, 'microsecond'):
                 value = value.replace(microsecond=0)
             value = str(value)
+        elif isinstance(value, datetime.date):
+            # MySQL will throw a warning if microseconds are given, because it
+            # doesn't support microseconds.
+            if settings.DATABASE_ENGINE == 'mysql' and hasattr(value, 'microsecond'):
+                value = datetime.datetime(value.year, value.month, value.day, microsecond=0)
+            value = str(value)
+
         return Field.get_db_prep_save(self, value)
 
     def get_db_prep_lookup(self, lookup_type, value):