def getall(self):
        try:
            spec = {'data': {'$exists': 1}}
            fields = {'_id': 0}
            sort = [('tid', 1)]
            cur = self.db.docs.find(spec, fields, sort=sort)
        except Exception as e:
            raise DatabaseException(e)
        return [Document(**row) for row in cur]
def linear_search(lst,size,value):
    i = 0
    while i < size:
        if lst[i] == value:
            return i
        i = i + 1
    return -1