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Let's say I have a model for my email address book:

class contact(db.Model):
    email = db.EmailProperty()
    image = #Hmm.

My contacts' images will be stored in the Blobstore, and served at various sizes.

So, should I use a db.ReferenceProperty(BlobInfo) such that I can serve it by doing:

get_serving_url(alice.image.key, size=x)

Or should I use a db.StringProperty so that I don't have to make the second read in order to get the key:

get_serving_url(alice.image, size=x)

Or should I use a db.LinkProperty for the base URL, post-fixing the size needed:

alice.image+'=sx'

I don't foresee needing anything other than the key, so I think the second is better than the first.

Though I am unsure if the third is best because I am unsure whether it is as efficient as creating a unique URL, which can be cached to avoid repeatedly generating the same thumbnail - or is this handled automagically in both cases?

Dan McGrath
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OJFord
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  • http://stackoverflow.com/questions/9362001/store-photos-in-blobstore-or-as-blobs-in-datastore-which-is-better-more-effici could be an interesting thing to look at. if you are SURE your blobs won't have > 1Mb and you're not really looking at cost, would be simpler to save them in the datastore. If you look at cost or have > 1Mb blobs.... blobstore is needed – Patrice Aug 07 '14 at 20:20
  • @Julldar I'm not comparing where to store my blobs - I'm asking how best to reference my *Blobstore* blob from a *Datastore* entity. – OJFord Aug 07 '14 at 20:22
  • then in that case, yeah 2nd > 1st, simply because you cut one get, so you have less calls, cheaper and faster results... for the 3rd.... might need a google engineer to weigh-in, I don't know how they magically handle some of these things – Patrice Aug 07 '14 at 20:23

1 Answers1

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After some experimentation, I think I can answer my own question.

Well, sort of. It turns out that the answer is "this wasn't a real problem to begin with".

While get_serving_url() gives the impression that something fancy is being done, actually the 'serving URL' is nothing more than a post-fixing of the supplied BlobKey.

What's more, supplying size=x merely appends =sx - there's nothing special, more or less efficient, about doing it this way. My second and third options, really are identical.

Finally, the __BlobInfo__ entity kind uses the BlobKey as its key name, so it is also easy to access from the other.

I have decided to use, and would suggest to anyone with the same dilemma, my third option:

imgBlob = db.LinkProperty()

It is then easy to:

  • append any resizing/cropping requirements
  • give a default value/make required without overloading put()
OJFord
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