Reading from the blobstore

[Rik Scarborough]

I see that you have to have the BlobKey to read a file from the blobstore.  How do you get that key from an already existing blob?

Or is there a better way to store a JSON or XML file that is transmitted to new users?

~Rik

[Robert Fischer]

Although the easier way to save the XML/JSON is to have the results
cached for you at the routes level:

https://gaelyk.appspot.com/tutorial/url-routing#caching

~~ Robert.
Science tells us we are merely beasts, but we don't feel like that. We
feel like angels trapped inside the bodies of beasts, forever craving
transcendence.
(VS Ramachandran, cognitive neuroscientist)

On Mon, Apr 9, 2012 at 11:12 AM, Robert Fischer <smokej...@gmail.com> wrote:
> Either you have the user give you the blobstore key (via the URL), or
> you have them give you a key which you look up in the DataStore (you
> can store Blobstore Keys as properties in the data store).
>
> ~~ Robert.
> Science tells us we are merely beasts, but we don't feel like that. We
> feel like angels trapped inside the bodies of beasts, forever craving
> transcendence.
> (VS Ramachandran, cognitive neuroscientist)

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[Robert Fischer]

Either you have the user give you the blobstore key (via the URL), or
you have them give you a key which you look up in the DataStore (you
can store Blobstore Keys as properties in the data store).

~~ Robert.
Science tells us we are merely beasts, but we don't feel like that. We
feel like angels trapped inside the bodies of beasts, forever craving
transcendence.
(VS Ramachandran, cognitive neuroscientist)

On Mon, Apr 9, 2012 at 10:52 AM, Rik Scarborough <rik...@gmail.com> wrote:

[Rik Scarborough]

So, when I save the blob to the blobstore, I have to save the key off to the datastore?

~Rik

[Rik Scarborough]

I'm already caching the data. The cache is then lost when the instance is shut down and I have to scan the entire table to reload the cache. If I can save a snapshot of the data, I only have to query the database for updates.

~Rik

[Robert Fischer]

When you save the blob to the blobstore, you have to provide some way
to look up the blob later on. This means deriving the key from a
user's later request. This usually involves storing the key to the
data store or giving it to the user. You can also give it to the user
and have the user give it back to you somehow — although in that case,
I'd also suggest a queue entry with the blob key to clean up the
blobstore when the blob expires.

~~ Robert.
Science tells us we are merely beasts, but we don't feel like that. We
feel like angels trapped inside the bodies of beasts, forever craving
transcendence.
(VS Ramachandran, cognitive neuroscientist)

[Guillaume Laforge]

For information...

JavaDoc of the BlobKey class:

https://developers.google.com/appengine/docs/java/javadoc/com/google/appengine/api/blobstore/BlobKey

One can get a string representation of the BlobKey calling blobKey.keyString (ie. getKeyString()).

You can store that string representation somewhere (datastore, memcache, url parameter, etc).

And then, you can call new BlobKey(stringRepresentation) to get the key.

Guillaume

Guillaume Laforge
Groovy Project Manager
SpringSource, a division of VMware

Blog: http://glaforge.appspot.com/

Social: @glaforge / Google+

[Rik Scarborough]

Ah, I think that last part may have been something I was doing wrong. I will try that tonight.

~Rik