"'Comment' has not been registered" and "False is not a read preference."

tumblelog/models.py

@@ -2,6 +2,10 @@
 from flask import url_for
 from tumblelog import db
 
+class Comment(db.EmbeddedDocument):
+    created_at = db.DateTimeField(default=datetime.datetime.now, required=True)
+    body = db.StringField(verbose_name="Comment", required=True)
+    author = db.StringField(verbose_name="Name", max_length=255, required=True)
 
 class Post(db.DynamicDocument):
     created_at = db.DateTimeField(default=datetime.datetime.now, required=True)
@@ -40,9 +44,3 @@ class Image(Post):
 class Quote(Post):
     body = db.StringField(required=True)
     author = db.StringField(verbose_name="Author Name", required=True, max_length=255)
-
-
-class Comment(db.EmbeddedDocument):
-    created_at = db.DateTimeField(default=datetime.datetime.now, required=True)
-    body = db.StringField(verbose_name="Comment", required=True)
-    author = db.StringField(verbose_name="Name", max_length=255, required=True)

tumblelog/requirements.txt

@@ -1,5 +1,6 @@
 flask
 flask-script
 WTForms
+pymongo == 2.8.1
 mongoengine
 flask_mongoengine