How to migrate from db.model to ndb.model?

Question

I have an old gae app that uses db.model. I understand that I should migrate to ndb.model. Is there an easy way or must I make many changes?

My code is fairly large and I have an old model that is db.model that I use to build index and search. Should I keep the old model and make a new ndb model or try and change the old model?

Some of the variables in the model are

cities = db.ListProperty(db.Key) #ndb.KeyProperty(repeated=True)
regions = db.ListProperty(db.Key) #ndb.KeyProperty(repeated=True)
blobs = db.ListProperty(db.BlobKey)  #ndb.BlobProperty(repeated=True)
primary_image = blobstore.BlobReferenceProperty()
usr = db.ReferenceProperty()  # ndb_model.KeyProperty()
hasimages = db.BooleanProperty(default=False,
                               verbose_name='has_images')
userID = db.StringProperty(verbose_name='User ID')
integer_price = db.IntegerProperty()
ip = ndb.StringProperty(verbose_name='ip')
ipcountry = db.StringProperty(indexed=False, verbose_name='origin')
tags = db.ListProperty(db.Category)
category = db.CategoryProperty(verbose_name='Category')
title = db.StringProperty(verbose_name='title')  # required
user = db.UserProperty(verbose_name='userid')
im = db.IMProperty(verbose_name='nickname')  # optional, xmpp
city = db.StringProperty()  # postaladdress should work instead
region = db.StringProperty()  # postaladdress should work instead
url = db.StringProperty(verbose_name='url')
geopt = db.GeoPtProperty(verbose_name='geopt')
text = db.TextProperty(verbose_name='text')

Answer 1

It shouldn't be particularly complex, and can be done incrementally, as you can mix db and ndb code in the same binary. See DB to NDB Client Library Migration.