BlobReferenceProperty and ReferenceProperty model design

I have a design question is BlobReferenceProperty basically ReferenceProperty? Should I do prefetch (suggested by Nick http://blog.notdot.net/2010/01/ReferenceProperty-prefetching-in-App-Engine) like for ReferenceProperty?

Currently I have this design:

class Entry(db.Model):
  creator     = db.ReferenceProperty(User, required=True, collection_name='entries')
  created_at  = db.DateTimeProperty(auto_now_add=True)

  # image
  image_id    = db.StringProperty() # key_name for Image
  image_url   = db.LinkProperty(indexed=False)
  width       = db.IntegerProperty(default=0, indexed=False)
  height      = db.IntegerProperty(default=0, indexed=False)


class Image(db.Model):
  created_at    = properties.DateTimeProperty(auto_now_add=True)
  blob          = blobstore.BlobReferenceProperty(required=True)
  filename      = db.StringProperty(indexed=False)
  published     = db.BooleanProperty(default=False, indexed=True)
  width         = db.IntegerProperty(default=0, indexed=False)
  height        = db.IntegerProperty(default=0, indexed=False)

Would this be better or worse? I have moved the blob to Entry instead.

class Entry(db.Model):
  creator     = db.ReferenceProperty(User, required=True, collection_name='entries')
  created_at  = db.DateTimeProperty(auto_now_add=True)

  # image     
  image_blob  = blobstore.BlobReferenceProperty(required=False)
  filename    = db.Stri开发者_JAVA百科ngProperty(indexed=False)
  image_id    = db.StringProperty()
  image_url   = db.LinkProperty(indexed=False)
  width       = db.IntegerProperty(default=0, indexed=False)
  height      = db.IntegerProperty(default=0, indexed=False)

Thanks.

Blobreference property is similar to db.ReferenceProperty, except for the fact that the entity actually lies in the blobstore. So prefetching ReferenceProperty applies to BlobReferenceProperty as well. blobstore.py also includes get_value_for_datastore using which you can prefetch blob entities.

Coming to your second question,moving the blob to Entry , it depends on your functionality.

You can use something like your first models if you are going to need a one-to-many relation between entry and image, if you want every entry to be able to match many images. I use a relationship somewhat like that:

class Article(db.Model):      
    user=db.UserProperty(verbose_name="userid") 

class Image(db.Model):       
    reference=db.ReferenceProperty(Article,collection_name='matched_images')
    primary_image = blobstore.BlobReferenceProperty()