Fix error if DBRef exists in DynamicEmbeddedDocument

[spengjie]

If assign a document to DynamicEmbeddedDocument, DBRef will be used to store the reference. The data can be stored successfully. But mongoengine.errors.FieldDoesNotExist error raised while reading the data from the database.

class Tag(Document): meta = {"collection": "tags"} name = StringField() class Post(DynamicEmbeddedDocument): pass class Page(Document): meta = {"collection": "pages"} post = EmbeddedDocumentField(Post) tag = Tag(name="test").save() post = Post(book_tag=tag) Page(post=post).save() page = Page.objects.first() # mongoengine.errors.FieldDoesNotExist raised here

Error message:
mongoengine.errors.FieldDoesNotExist: The fields "{'_ref'}" do not exist on the document "XXX"
Solution:
Dereference the field value if it is a dict with both '_cls' and '_ref' in it.