Save no longer tramples over documents now sets or unsets explicit fields.

Fixes #146, refs #18
Thanks @zhangcheng for the initial code

docs/changelog.rst

@@ -5,9 +5,10 @@ Changelog
 Changes in dev
 ==============
 
+- Fixed saving so sets updated values rather than overwrites
 - Added ComplexDateTimeField - Handles datetimes correctly with microseconds
-- Added ComplexBaseField - for improved flexibility and performance.
+- Added ComplexBaseField - for improved flexibility and performance
-- Added get_FIELD_display() method for easy choice field displaying.
+- Added get_FIELD_display() method for easy choice field displaying
 - Added queryset.slave_okay(enabled) method
 - Updated queryset.timeout(enabled) and queryset.snapshot(enabled) to be chainable
 - Added insert method for bulk inserts

mongoengine/base.py

@@ -92,6 +92,9 @@ class BaseField(object):
         """Descriptor for assigning a value to a field in a document.
         """
         instance._data[self.name] = value
+        # If the field set is in the _present_fields list add it so we can track
+        if hasattr(instance, '_present_fields') and self.name not in instance._present_fields:
+            instance._present_fields.append(self.name)
 
     def to_python(self, value):
         """Convert a MongoDB-compatible type to a Python type.
@@ -592,13 +595,14 @@ class BaseDocument(object):
             if field.choices:  # dynamically adds a way to get the display value for a field with choices
                 setattr(self, 'get_%s_display' % attr_name, partial(self._get_FIELD_display, field=field))
 
-            # Use default value if present
             value = getattr(self, attr_name, None)
             setattr(self, attr_name, value)
+
         # Assign initial values to instance
         for attr_name in values.keys():
             try:
-                setattr(self, attr_name, values.pop(attr_name))
+                value = values.pop(attr_name)
+                setattr(self, attr_name, value)
             except AttributeError:
                 pass
 
@@ -739,7 +743,6 @@ class BaseDocument(object):
             cls = subclasses[class_name]
 
         present_fields = data.keys()
-
         for field_name, field in cls._fields.items():
             if field.db_field in data:
                 value = data[field.db_field]

mongoengine/document.py

@@ -95,6 +95,16 @@ class Document(BaseDocument):
             collection = self.__class__.objects._collection
             if force_insert:
                 object_id = collection.insert(doc, safe=safe, **write_options)
+            elif '_id' in doc:
+                # Perform a set rather than a save - this will only save set fields
+                object_id = doc.pop('_id')
+                collection.update({'_id': object_id}, {"$set": doc}, upsert=True, safe=safe, **write_options)
+
+                # Find and unset any fields explicitly set to None
+                if hasattr(self, '_present_fields'):
+                    removals = dict([(k, 1) for k in self._present_fields if k not in doc and k != '_id'])
+                    if removals:
+                        collection.update({'_id': object_id}, {"$unset": removals}, upsert=True, safe=safe, **write_options)
             else:
                 object_id = collection.save(doc, safe=safe, **write_options)
         except pymongo.errors.OperationFailure, err:

setup.py

@@ -45,6 +45,6 @@ setup(name='mongoengine',
       long_description=LONG_DESCRIPTION,
       platforms=['any'],
       classifiers=CLASSIFIERS,
-      install_requires=['pymongo', 'blinker', 'django>=1.3'],
+      install_requires=['pymongo', 'blinker', 'django==1.3'],
       test_suite='tests',
 )

tests/document.py

@@ -789,6 +789,90 @@ class DocumentTest(unittest.TestCase):
         except ValidationError:
             self.fail()
 
+    def test_update(self):
+        """Ensure that an existing document is updated instead of be overwritten.
+        """
+        # Create person object and save it to the database
+        person = self.Person(name='Test User', age=30)
+        person.save()
+
+        # Create same person object, with same id, without age
+        same_person = self.Person(name='Test')
+        same_person.id = person.id
+        same_person.save()
+
+        # Confirm only one object
+        self.assertEquals(self.Person.objects.count(), 1)
+
+        # reload
+        person.reload()
+        same_person.reload()
+
+        # Confirm the same
+        self.assertEqual(person, same_person)
+        self.assertEqual(person.name, same_person.name)
+        self.assertEqual(person.age, same_person.age)
+
+        # Confirm the saved values
+        self.assertEqual(person.name, 'Test')
+        self.assertEqual(person.age, 30)
+
+        # Test only / exclude only updates included fields
+        person = self.Person.objects.only('name').get()
+        person.name = 'User'
+        person.save()
+
+        person.reload()
+        self.assertEqual(person.name, 'User')
+        self.assertEqual(person.age, 30)
+
+        # test exclude only updates set fields
+        person = self.Person.objects.exclude('name').get()
+        person.age = 21
+        person.save()
+
+        person.reload()
+        self.assertEqual(person.name, 'User')
+        self.assertEqual(person.age, 21)
+
+        # Test only / exclude can set non excluded / included fields
+        person = self.Person.objects.only('name').get()
+        person.name = 'Test'
+        person.age = 30
+        person.save()
+
+        person.reload()
+        self.assertEqual(person.name, 'Test')
+        self.assertEqual(person.age, 30)
+
+        # test exclude only updates set fields
+        person = self.Person.objects.exclude('name').get()
+        person.name = 'User'
+        person.age = 21
+        person.save()
+
+        person.reload()
+        self.assertEqual(person.name, 'User')
+        self.assertEqual(person.age, 21)
+
+        # Confirm does remove unrequired fields
+        person = self.Person.objects.exclude('name').get()
+        person.age = None
+        person.save()
+
+        person.reload()
+        self.assertEqual(person.name, 'User')
+        self.assertEqual(person.age, None)
+
+        person = self.Person.objects.get()
+        person.name = None
+        person.age = None
+        person.save()
+
+        person.reload()
+        self.assertEqual(person.name, None)
+        self.assertEqual(person.age, None)
+
     def test_delete(self):
         """Ensure that document may be deleted using the delete method.
         """