Question

On Google App Engine, I used to store images in db:

class Images(db.Model):
    image = db.BlobProperty()

After inserting an entity (say, ‘advertisement’), I can use the following to render an image in an HTML page:

    <img src="/image?entity_id={{advertisement.key}}" class="advertise" /></a><br />

At the server side, the image is retrieved by:

class GetImage(webapp2.RequestHandler):
    def get(self):
        entity_id = self.request.get('entity_id')
        entity = db.get(entity_id)
        if entity and entity.image:
            self.response.headers['Content-Type'] = 'image/png'
            self.response.out.write(entity.image)

And now, I would like to convert the datastore to ndb, but I am having troubles.

1. Can I still use ‘Advertisement.key’ in the HTML?

2. There is no db.get() method in ndb. How do I retrieve an entity by its key?

Answer 1

You can use ndb.Key.to_old_key()

https://developers.google.com/appengine/docs/python/ndb/keyclass#Key_to_old_key

<img src="/image?entity_id={{advertisement.key.to_old_key()}}" class="advertise" />

to retrieve ndb entities use key.urlsafe:

class Images(ndb.Model):
  image = ndb.BlobProperty()

<img src="/image?entity_id={{advertisement.key.urlsafe()}}" class="advertise" /></a><br />

class GetImage(webapp2.RequestHandler):
  def get(self):
    entity_id = self.request.get('entity_id')
    entity = ndb.Key(urlsafe=entity_id).get()
    if entity and entity.image:
      self.response.headers['Content-Type'] = 'image/png'
      self.response.out.write(entity.image)

https://developers.google.com/appengine/docs/python/ndb/keyclass#Key_urlsafe