Fixed distinct casting issue with ListField of EmbeddedDocuments (#470)

docs/changelog.rst

@@ -4,6 +4,7 @@ Changelog
 
 Changes in 0.8.5
 ================
+- Fixed distinct casting issue with ListField of EmbeddedDocuments (#470)
 - Fixed Django 1.6 sessions (#454, #480)
 
 Changes in 0.8.4

mongoengine/queryset/base.py

@@ -621,8 +621,15 @@ class BaseQuerySet(object):
         try:
             field = self._fields_to_dbfields([field]).pop()
         finally:
-            return self._dereference(queryset._cursor.distinct(field), 1,
-                                     name=field, instance=self._document)
+            distinct = self._dereference(queryset._cursor.distinct(field), 1,
+                                         name=field, instance=self._document)
+
+            # We may need to cast to the correct type eg. ListField(EmbeddedDocumentField)
+            doc_field = getattr(self._document._fields.get(field), "field", None)
+            instance = getattr(doc_field, "document_type", False)
+            if instance:
+                distinct = [instance(**doc) for doc in distinct]
+            return distinct
 
     def only(self, *fields):
         """Load only a subset of this document's fields. ::

tests/queryset/queryset.py

@@ -2519,6 +2519,27 @@ class QuerySetTest(unittest.TestCase):
 
         Product.drop_collection()
 
+    def test_distinct_ListField_EmbeddedDocumentField(self):
+
+        class Author(EmbeddedDocument):
+            name = StringField()
+
+        class Book(Document):
+            title = StringField()
+            authors = ListField(EmbeddedDocumentField(Author))
+
+        Book.drop_collection()
+
+        mark_twain = Author(name="Mark Twain")
+        john_tolkien = Author(name="John Ronald Reuel Tolkien")
+
+        book = Book(title="Tom Sawyer", authors=[mark_twain]).save()
+        book = Book(title="The Lord of the Rings", authors=[john_tolkien]).save()
+        book = Book(title="The Stories", authors=[mark_twain, john_tolkien]).save()
+        authors = Book.objects.distinct("authors")
+
+        self.assertEquals(authors, [mark_twain, john_tolkien])
+
     def test_custom_manager(self):
         """Ensure that custom QuerySetManager instances work as expected.
         """