How to save a list of blob keys that belong to an entity?

Question

With my webapp users can upload images as blobs in GAE. I want an easy connection between the article and the images (blobs) so I tried the following:

class Article(db.Model):
    blobs = db.ListProperty(db.Key)

and then in the blobstoreuploadhandler:

for upload in self.get_uploads():
    try:
        article.blobs.append(upload.key())

But then it gets an exception:

 /upload_form 404 3753ms 1kb Mozilla/5.0 (Windows NT 6.1; rv:28.0) Gecko/20100101 Firefox/28.0 module=default version=leakagefix
0.1.0.30 - - [20/Mar/2014:04:46:27 -0700] "POST /upload_form HTTP/1.1" 404 1331 "http://www.koolbusiness.com/ai" "Mozilla/5.0 (Windows NT 6.1; rv:28.0) Gecko/20100101 Firefox/28.0" "www.koolbusiness.com" ms=3754 cpu_ms=2036 cpm_usd=0.000149 app_engine_release=1.9.1 instance=00c61b117c8167bb98b5f7f69bd68254df45fe64
E 2014-03-20 12:46:27.190
There was an exception:Items in the blobs list must all be Key instances
E 2014-03-20 12:46:27.216
Items in the blobs list must all be Key instances

Can you tell me how it should be done and what was wrong with this attempt?

Answer 1

Blob keys are different from Datastore keys. Use BlobKey class:

https://developers.google.com/appengine/docs/python/blobstore/blobkeyclass?hl=ja