pymongo: query mongo by object

[Jeff]

Hello,
having collection with compound _id field: {_id:{i:1, k:2}, data:"bar"}

// nothing found
collection.find_one({'_id':{"i" : 1, "k" : 2}})

// found, but slow, because index on _id object is not used
collection.find_one({"_id.i" : 1, "_id.k" : 2})


is this bug in pymongo? why the first query doesn't work otherwise?


Thanks
Jeff

[Jeff]

it happens only on this specific collection. I've created test one with similar structure and it works fine there. Still have no idea why it doesn't work with the real data

[Bernie Hackett]

why the first query doesn't work otherwise?

Because the python dict type is an unordered hash. See this FAQ answer:

https://api.mongodb.com/python/current/faq.html#key-order-in-subdocuments-why-does-my-query-work-in-the-shell-but-not-pymongo