mongodb-query

With the reference of my previous question, I have a question about $lookup with add some conditions. You may get enough reference about question from below link description. Photo: {_id: 1, photo_name: '1.jpg', photo_description: 'description 1', album_id: 1, flag:1 }, {_id: 2, photo_name: '2.jpg', photo_description: 'description 2', album_id: 1, flag:1 }, {_id: 3, photo_name: '3.jpg', photo_description: 'description 3', album_id: 1, flag:1 }, {_id: 4, photo_name: '4.jpg', photo_description: 'description 4', album_id: 2, flag:0 }, {_id: 5, photo_name: '5.jpg', photo_description: 'description

When I try to remove a document in collection in MongoDB . It didn't remove because the collection is capped . My question is why? And is there a solution or other function can remove the document in this case? No You cannot delete documents from a capped collection. And there is no possible workaround. The only thing you can do is drop() the collection. Gaurav Radadiya You can not use remove function for capped collection. There are some restrictions on capped collections. Also you can refer this document for capped collection in mongoDB. 来源： https://stackoverflow.com/questions/33048282/how

In mongodb there are documents in the following structure: { "_id" : ObjectId("52d017d4b60fb046cdaf4851"), "dates" : [ 1399518702000, 1399126333000, 1399209192000, 1399027545000 ], "dress_number" : "4", "name" : "J. Evans", "numbers" : [ "5982", "5983", "5984", "5985" ] } Is it possible unwind data from multiple arrays and get only paired elements from arrays: { "dates": "1399518702000", "numbers": "5982" }, { "dates": "1399126333000", "numbers": "5983" }, { "dates": "1399209192000", "numbers": "5984" }, { "dates": "1399027545000", "numbers": "5985" } From version 3.2 you can do it with

I want to retrieve values of only certain keys from a MongoDB collection. But, the collection has some keys which have a 'space' in their name like: "Parent":{"key1": //some string, "key2": //some string, "key 3": //some string} I know this is a wrong approach as there shouldn't ideally be spaces in a key name but nevertheless how do I query this key? I am using Python and PyMongo. For normal keys I can do this: db.coll_name.find({"key": "India"}, {"_id": 0, "Parent.key1": 1, "Parent.key2": 1}) So how do I use the key "Parent['key 3']" in the second argument of the above query? Is there any

Suppose I have a single document in my mongo collection that looks like this: { "_id": 123, "field_to_prune": { "keep_field_1": "some value", "random_field_1": "some value", "keep_field_2": "some value", "random_field_2": "some value", "random_field_3": "some value" } } I want to prune that document to look like this: { "_id": 123, "field_to_prune": { "keep_field_1": "some value", "keep_field_2": "some value" } } However, my issue is that I don't know what the "random" field names are. In mongo, how would i $unset all fields except a couple of known fields? I can think of a couple of ways, but