Use Django views for handling blobstore uploads

Question

In stead of using the BlobstoreUploadHandler supplied in AppEngine, I\'d prefer to use a Django view, so I can keep all the urls and view functions together. Howeve

Answer 1

The key info isn't directly in the file, it's in file.blobstore_info.key()

1. post your form containing your image to a url created using blobstore.create_upload_url():

   from google.appengine.ext import blobstore
   
   upload_url = blobstore.create_upload_url('/add_image/')
   

the created url will save the image in the blobstore and redirect the request (with modified file object) to /add_image/

2. define a url pattern and view for /add_image/ and handle the image:

   def add_action_image(request):
       image = request.data.get('image')
       image_key = image.blobstore_info.key()
       ... addl' logic to save a record with the image_key...
   

Answer 2

I had the same problem yesterday. Thanks to your post I realizad that the problem was django and his class views. I finally use a code that I have since 2011 and it still works. It does not use BlobstoreUploadHandler, but it gets the blob_infos from the request after automatically upload it to blobstore.

You can use that function in the next way from your callback django function or class (I finally did not try it in a class view from Django but I think it will work. Currently I'm using it in a function view from Django with its request):

media_blobs = get_uploads(request, populate_post=True)

The function is the next:

import cgi 
from google.appengine.ext import blobstore
def get_uploads(request, field_name=None, populate_post=False):
    """Get uploads sent to this handler.
    Args:
    field_name: Only select uploads that were sent as a specific field.
    populate_post: Add the non blob fields to request.POST
    Returns:
      A list of BlobInfo records corresponding to each upload.
      Empty list if there are no blob-info records for field_name.
    """

    if hasattr(request,'__uploads') == False:
        request.META['wsgi.input'].seek(0)
    ja = request.META['wsgi.input']
    fields = cgi.FieldStorage(request.META['wsgi.input'], environ=request.META)

    request.__uploads = {}
    if populate_post:
        request.POST = {}

    for key in fields.keys():
        field = fields[key]
        if isinstance(field, cgi.FieldStorage) and 'blob-key' in field.type_options:
            request.__uploads.setdefault(key, []).append(blobstore.parse_blob_info(field))
        elif populate_post:
            if isinstance(field, list):
                request.POST[key] = [val.value for val in field]
            else:
                request.POST[key] = field.value
    if field_name:
        try:
            return list(request.__uploads[field_name])
        except KeyError:
            return []
    else:
        results = []
        for uploads in request.__uploads.itervalues():
            results += uploads
        return results

The last function is not mine. I do not remember where I got it three or four years ago. But I think it will help someone.

UPDATE:

You also can use a view handler of webapp.WSGIApplication and at the same time use django. This way will allow you to use BlobstoreUploadHandler and BlobstoreDownloadHandler (for video stream as example). You only need to add the view class in main.py and create its handler:

class ServeVideoHandler(blobstore_handlers.BlobstoreDownloadHandler):
    def get(self, resource):
        ...

downloader_handler = webapp.WSGIApplication([('/pathA/pathB/([A-Za-z0-9\-\=_]+)', ServeVideoHandler),], debug=True)

And in app.yaml add the handler before the script main.application that contains your django app.

- url: /pathA/pathB/(.+)
  script: main.downloader_handler

Answer 3

It took me a long time to find, but the content_type: message/external-body requires extra parameters, to find the actual file, in AppEngine's case, this is the blob-key. However, Django doesn't support these extra content_type parameters, so they are indeed lost in the process. There seems to be a patch, but I don't think it's in the AppEngine Django version yet.

https://code.djangoproject.com/ticket/13721

Answer 4

As you noted, BlobstoreUploadHandler is open source, so you can see the logic they use to parse the key out of the request params. Note that request.params just includes variables from both the query string and the request body (for POST requests). So you might want to start with your djnago request's REQUEST object.