Demonstration of MongDB FileField's Losing File Reference

demo.py

# -*- coding:utf-8 -*-

import tempfile

import pymongo, gridfs, mongoengine

class TheDocument(mongoengine.Document):
    the_file = mongoengine.FileField()

if __name__ == '__main__':

    connection = pymongo.Connection('127.0.0.1', 27017)
    db = connection['TestDB']

    mongoengine.connect('TestDB', host='127.0.0.1', port=27017)

    with tempfile.TemporaryFile() as f:
        f.write("Hello World!")
        f.flush()

        print '==== ==== Test A: Without Initial FileField Value ==== ===='
        doc_a = TheDocument()
        doc_a.save()
        print 'New Document: %s' % doc_a.id

        # Query the document just created
        doc_b = TheDocument.objects.with_id(doc_a.id)
        print 'Query the same document: %s' % doc_b.id

        print 'Call replace() ...'
        doc_b.the_file.replace(f, filename='doc_b')
        print 'After replace(), grid_id is %s' % doc_b.the_file.grid_id

        doc_b.save()
        print 'Save document ...'

        # Query Again
        doc_c = TheDocument.objects.with_id(doc_b.id)
        print 'Query again: %s' % doc_c.id
        print 'grid_id is %s' % doc_c.the_file.grid_id



        print '\n==== ==== Test B: With Initial FileField Value ==== ===='
        doc_d = TheDocument(the_file='')
        doc_d.save()
        print 'New Document: %s' % doc_d.id

        doc_e = TheDocument.objects.with_id(doc_d.id)
        print 'Query the same document: %s' % doc_e.id

        print 'Call replace() ...'
        doc_e.the_file.replace(f, filename='doc_e')
        print 'After replace(), grid_id is %s' % doc_e.the_file.grid_id

        doc_e.save()
        print 'Save document ...'

        doc_f = TheDocument.objects.with_id(doc_e.id)
        print 'Query again: %s' % doc_f.id
        print 'grid_id is %s' % doc_f.the_file.grid_id

    print '\n==== ==== MongoDB GridFS File ==== ===='
    grid_fs = gridfs.GridFS(db)
    print grid_fs.list()

    connection.drop_database('TestDB')
    connection.close()