Fixes DateTimeField handling of date objects.

Fixes #191

mongoengine/fields.py

@@ -232,12 +232,16 @@ class DateTimeField(BaseField):
     """A datetime field.
 
     Note: Microseconds are rounded to the nearest millisecond.
-      Pre UTC microsecond support is effecively broken see
+      Pre UTC microsecond support is effecively broken.
-      `tests.field.test_datetime` for more information.
+      Use :class:`~mongoengine.fields.ComplexDateTimeField` if you
+      need accurate microsecond support.
     """
 
     def validate(self, value):
-        assert isinstance(value, datetime.datetime)
+        assert isinstance(value, (datetime.datetime, datetime.date))
+
+    def to_mongo(self, value):
+        return self.prepare_query_value(None, value)
 
     def prepare_query_value(self, op, value):
         if value is None:

tests/fields.py

@@ -182,6 +182,9 @@ class FieldTest(unittest.TestCase):
         log.time = datetime.datetime.now()
         log.validate()
 
+        log.time = datetime.date.today()
+        log.validate()
+
         log.time = -1
         self.assertRaises(ValidationError, log.validate)
         log.time = '1pm'
@@ -199,6 +202,15 @@ class FieldTest(unittest.TestCase):
 
         LogEntry.drop_collection()
 
+        # Test can save dates
+        log = LogEntry()
+        log.date = datetime.date.today()
+        log.save()
+        log.reload()
+        self.assertEquals(log.date.date(), datetime.date.today())
+
+        LogEntry.drop_collection()
+
         # Post UTC - microseconds are rounded (down) nearest millisecond and dropped
         d1 = datetime.datetime(1970, 01, 01, 00, 00, 01, 999)
         d2 = datetime.datetime(1970, 01, 01, 00, 00, 01)