Ported fix for Circular Reference bug to Master

Ready for a 0.5.2 release

AUTHORS

@@ -67,3 +67,5 @@ that much better:
  * Gareth Lloyd
  * Albert Choi
  * John Arnfield
+ * Julien Rebetez
+

docs/changelog.rst

@@ -2,6 +2,11 @@
 Changelog
 =========
 
+Changes in v0.5.2
+=================
+
+- A Robust Circular reference bugfix
+
 Changes in v0.5.1
 =================
 

mongoengine/base.py

@@ -724,18 +724,32 @@ def _mark_as_changed(self, key):
         if hasattr(self, '_changed_fields') and key not in self._changed_fields:
             self._changed_fields.append(key)
 
-    def _get_changed_fields(self, key=''):
+    def _get_changed_fields(self, key='', inspected=None):
         """Returns a list of all fields that have explicitly been changed.
         """
         from mongoengine import EmbeddedDocument
         _changed_fields = []
         _changed_fields += getattr(self, '_changed_fields', [])
-        for field_name in self._fields:
+
+        inspected = inspected or set()
+        if hasattr(self, 'id'):
+            if self.id in inspected:
+                return _changed_fields
+            inspected.add(self.id)
+
+        field_list = self._fields.copy()
+
+        for field_name in field_list:
             db_field_name = self._db_field_map.get(field_name, field_name)
             key = '%s.' % db_field_name
             field = getattr(self, field_name, None)
-            if isinstance(field, EmbeddedDocument) and db_field_name not in _changed_fields:  # Grab all embedded fields that have been changed
-                _changed_fields += ["%s%s" % (key, k) for k in field._get_changed_fields(key) if k]
+            if hasattr(field, 'id'):
+                if field.id in inspected:
+                    continue
+                inspected.add(field.id)
+
+            if isinstance(field, (EmbeddedDocument,)) and db_field_name not in _changed_fields:  # Grab all embedded fields that have been changed
+                _changed_fields += ["%s%s" % (key, k) for k in field._get_changed_fields(key, inspected) if k]
             elif isinstance(field, (list, tuple, dict)) and db_field_name not in _changed_fields:  # Loop list / dict fields as they contain documents
                 # Determine the iterator to use
                 if not hasattr(field, 'items'):
@@ -746,8 +760,7 @@ def _get_changed_fields(self, key=''):
                     if not hasattr(value, '_get_changed_fields'):
                         continue
                     list_key = "%s%s." % (key, index)
-                    _changed_fields += ["%s%s" % (list_key, k) for k in value._get_changed_fields(list_key) if k]
-
+                    _changed_fields += ["%s%s" % (list_key, k) for k in value._get_changed_fields(list_key, inspected) if k]
         return _changed_fields
 
     def _delta(self):

tests/dereference.py

@@ -188,6 +188,51 @@ def __repr__(self):
 
         self.assertEquals("[<Person: Mother>, <Person: Daughter>]", "%s" % Person.objects())
 
+    def test_circular_tree_reference(self):
+        """Ensure you can handle circular references with more than one level
+        """
+        class Other(EmbeddedDocument):
+            name = StringField()
+            friends = ListField(ReferenceField('Person'))
+
+        class Person(Document):
+            name = StringField()
+            other = EmbeddedDocumentField(Other, default=lambda: Other())
+
+            def __repr__(self):
+                return "<Person: %s>" % self.name
+
+        Person.drop_collection()
+        paul = Person(name="Paul")
+        paul.save()
+        maria = Person(name="Maria")
+        maria.save()
+        julia = Person(name='Julia')
+        julia.save()
+        anna = Person(name='Anna')
+        anna.save()
+
+        paul.other.friends = [maria, julia, anna]
+        paul.other.name = "Paul's friends"
+        paul.save()
+
+        maria.other.friends = [paul, julia, anna]
+        maria.other.name = "Maria's friends"
+        maria.save()
+
+        julia.other.friends = [paul, maria, anna]
+        julia.other.name = "Julia's friends"
+        julia.save()
+
+        anna.other.friends = [paul, maria, julia]
+        anna.other.name = "Anna's friends"
+        anna.save()
+
+        self.assertEquals(
+            "[<Person: Paul>, <Person: Maria>, <Person: Julia>, <Person: Anna>]",
+            "%s" % Person.objects()
+        )
+
     def test_generic_reference(self):
 
         class UserA(Document):