Sorting in MongoDB's aggregation framework

aggregation-framework, mongodb, pymongo

Solution

From the docs:

As python dictionaries don’t maintain order you should use `SON` or `collections.OrderedDict` where explicit ordering is required eg "$sort"

from bson.son import SON
db.users.aggregate([
    {"$sort": SON([("posts", 1), ("age", -1)])}
])

Problem

The docs for MongoDB seem to suggest that in order to sort the results of an `aggregate` call you should specify a dictionary/object like this: ``` db.users.aggregate( { $sort : { age : -1, posts: 1 } } ); ``` This is supposed to sort by `age` and then by `posts`. What do I do if I want to sort by `posts` and then by `age`? Changing the order of the keys seems to have no effect, probably because this is a JS object's properties. In other words, sorting, it seems, is always according to the lexical order of the keys, which seems rather odd as a design choice... Am I missing something? Is there a way to specify an ordered list of keys to sort by?

Original source