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POWhy does the Google App Engine python Blob care about what is stored in it
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  1. POWhy does the Google App Engine python Blob care about what is stored in it
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    copied!<p>I have been struggling with some very basic understanding of how google app engine store data</p> <p>I have defined a class defining a client profile as such :</p> <pre><code>class ClientProfile(ndb.Model): nickname = ndb.StringProperty(required=True) photo = ndb.BlobProperty() uuid = ndb.StringProperty(required = True) </code></pre> <p>I retrieve an image data only uploading image.src via a POST using jquery.ajax(...)</p> <p>The data are properly sent to Google app engine and I can assign them to a variable with</p> <pre><code>imagesrc = self.request.get('photosrcbase64') </code></pre> <p>The data content is something looking like : </p> <pre><code>"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA... </code></pre> <p>So fare so good, the data is an image/png and the encoding is Base64, but should I care if it end in a Blob ?</p> <p>Now if I try to put the data in the photo Blob</p> <p>with for example :</p> <p><code>clientprofile.photo = imagesrc</code> I get a Bad Value Error, in this case :</p> <blockquote> <p>BadValueError: Expected str, got u'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAMgAA</p> </blockquote> <p>I tried all kind of combinations using different solutions and get back all kind of BadValue or type errors.</p> <p>My question are : 1) Why does the Blob care, if it is a binary storage, I should be able to dump in it anything without having to interpret it and/or convert it, so is a Blob really a Binary/Raw storage and why does it care about how things are stored in it ?</p> <p>2) I have started having problems with this 2 years ago when still using db instead of ndb, I found a solution that I did not understand by stripping out the MIME information at the beginning of the data string, decoding the string Base64 and using db.Blob(...) to convert my string to a Blob. the problem is that db.Blob() does not seem to exist in ndb so I can't do this any more.</p> <p>I am convinced that I am missing something fundamental in the way informations are exchanged between google app engine and the browser and thank you in advance for a mind clearing answer</p>
 

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