download file from mongo gridfs with python - mongodb

Question

I have uploaded files to the mongo.But when I want to download from mongo by httpresonse on the web browser,that did not work.
Here is the views.py:
if filename is not None:
file_ = db.fs.files.find_one({
'filename':filename
})
file_id = file_['_id']
wrapper = fs.get(file_id).read()
response = StreamingHttpResponse(FileWrapper(wrapper),content_type=file_['contentType'])
response['Content-Disposition'] = 'attachment; filename=%s' % str(filename)
response['Content-Length'] = file_['length']
return response
I got this error:
Traceback (most recent call last):
File "/usr/lib/python2.7/wsgiref/handlers.py", line 86, in run
self.finish_response()
File "/usr/lib/python2.7/wsgiref/handlers.py", line 126, in finish_response
for data in self.result:
File "/usr/local/lib/python2.7/dist-packages/django/utils/six.py", line 473, in next
return type(self).__next__(self)
File "/usr/local/lib/python2.7/dist-packages/django/http/response.py", line 292, in __next__
return self.make_bytes(next(self._iterator))
File "/usr/lib/python2.7/wsgiref/util.py", line 30, in next
data = self.filelike.read(self.blksize)
AttributeError: 'str' object has no attribute 'read'
But when I change the StreamingHttpResponse to HttpResponse,the error is as follow:
[30/Jul/2014 17:29:43] "GET /download/cs101/ HTTP/1.1" 200 664
/usr/lib/python2.7/wsgiref/handlers.py:126: DeprecationWarning:
Creating streaming responses with `HttpResponse` is deprecated.
Use `StreamingHttpResponse`instead if you need the streaming behavior.
for data in self.result:
Traceback (most recent call last):
File "/usr/lib/python2.7/wsgiref/handlers.py", line 86, in run
self.finish_response()
File "/usr/lib/python2.7/wsgiref/handlers.py", line 126, in finish_response
for data in self.result:
File "/usr/local/lib/python2.7/dist-packages/django/utils/six.py", line 473, in next
return type(self).__next__(self)
File "/usr/local/lib/python2.7/dist-packages/django/http/response.py", line 292, in __next__
return self.make_bytes(next(self._iterator))
File "/usr/lib/python2.7/wsgiref/util.py", line 30, in next
data = self.filelike.read(self.blksize)
AttributeError: 'str' object has no attribute 'read'
Thanks in advance!

Answer 1

You're calling the read method in:
wrapper = fs.get(file_id).read()
So you're getting a str (assuming Python 2, if 3, you're getting bytes). FileWrapper needs file like object, which of course str is not one.
Try to use:
wrapper = fs.get(file_id)
This will return file like object.
OTOH, pymongo's .get() returns a GridOut instance, which already supports iteration, so why not try something like:
wrapper = fs.get(file_id)
response = StreamingHttpResponse(wrapper, content_type=file_['contentType'])