def get_dos_from_id(self, task_id):
        """
        Overrides the get_dos_from_id for the MIT gridfs format.
        """
        args = {'task_id': task_id}
        fields = ['calculations']
        structure = self.get_structure_from_id(task_id)
        dosid = None
        for r in self.query(fields, args):
            dosid = r['calculations'][-1]['dos_fs_id']
        if dosid is not None:
            self._fs = gridfs.GridFS(self.db, 'dos_fs')
            with self._fs.get(dosid) as dosfile:
                s = dosfile.read()
                try:
                    d = json.loads(s)
                except:
                    s = zlib.decompress(s)
                    d = json.loads(s.decode("utf-8"))
                tdos = Dos.from_dict(d)
                pdoss = {}
                for i in range(len(d['pdos'])):
                    ados = d['pdos'][i]
                    all_ados = {}
                    for j in range(len(ados)):
                        orb = Orbital(j)
                        odos = ados[str(orb)]
                        all_ados[orb] = {Spin(int(k)): v
                                         for k, v
                                         in odos['densities'].items()}
                    pdoss[structure[i]] = all_ados
                return CompleteDos(structure, tdos, pdoss)
        return None
Overrides the get_dos_from_id for the MIT gridfs format.