Q:

Creating URLs for entities stored on the Google Appengine datastore

I have a bunch of Blob-typed entities stored on the datastore. Each of them stores video-data bytes. I intend to use the video HTML5 tag to display the video but I can't find anyway of creating a URL for the Blobs. Any suggestions?

A:

You can not create a URL for blob typed properties automatically, or for properties of any type, or for entities for that matter. You will have to write a handler that loads the entity and serves the blob. 
A better solution would be to use the BlobStore API. You still cannot serve them automatically, but the storage is better suited to blobs. You can use use BlobStoreService.serve to do most of the work for you.
Or you could use the cloud file API. This automatically generates a public URL for blobs you create.

