Try the following in the shell, it will iterate each item within a collection and try to match each document based on ID. Say we have 2 collections db.col1 and db.col2: > db.col1.find() { “_id” : 1, “item” : 1 } { “_id” : 2, “item” : 2 } { “_id” : 3, “item” : … Read more
exit from mongoshell with quit() and try to run command in regular command prompt, it will work
in my case most ids will be generated within a large number of mobile clients, not within a limited set of servers. I wonder if in this case, there is a justified concern. That sounds like very bad architecture to me. Are you using a two-tier architecture? Why would the mobile clients have direct access … Read more
Dbref in my opinion should be avoided when work with mongodb, at least if you work with big systems that require scalability. As i know all drivers make additional request to load DBRef, so it’s not ‘join‘ within database, it is very expensive. Is there a way to reference other documents without having the somewhat … Read more
If you specified the correct port and still not able to connect to mongodb running in docker (like me), make sure you are using the service name (or container name) in your connection URL, e.g. mongodb://mongodb_service:27017/mydb, which is defined in your docker-compose.yml : services: mongodb_service: image: mongo I was using the hostname value and that’s … Read more
Inspired by this example on mongo’s website. GENERATE DUMMY DATA: > db.stack.insert({a:1,b:1,c:1,active:1}) > db.stack.insert({a:1,b:1,c:2,active:0}) > db.stack.insert({a:1,b:2,c:3,active:1}) > db.stack.insert({a:1,b:2,c:2,active:0}) > db.stack.insert({a:2,b:1,c:3,active:1}) > db.stack.insert({a:2,b:1,c:10,active:1}) > db.stack.insert({a:2,b:2,c:10,active:0}) > db.stack.insert({a:2,b:2,c:5,active:1}) MONGO QUERY: > db.stack.aggregate( … {$match:{active:1}}, … {$group:{_id:{a:”$a”, b:”$b”}, csum:{$sum:”$c”}}}, … {$sort:{“_id.a”:1}}) RESULT: {“result” : [ {“_id” : {“a” : 1,”b” : 2},”csum” : 3}, {“_id” : {“a” : … Read more
This behavior isn’t related to $lookup, it’s because the default behavior for $unwind is to omit documents where the referenced field is missing or an empty array. To preserve the unwound documents even when profile.universities is an empty array, you can set its preserveNullAndEmptyArrays option to true: db.users.aggregate([ { $unwind: “$profile”, $unwind: { path: “$profile.universities”, … Read more
You can run server-side code with db.eval(). db.eval(function() { db.collection.find({tag : “refurb”}).forEach(function(e) { e.Price = e.Price * 0.5; db.collection.save(e); }); }); Note this will block the DB, so it’s better to do find-update operation pair. See https://docs.mongodb.com/manual/core/server-side-javascript/
@Dummy is correct that bulk operations are generally faster than individual inserts, however, from version 2.6 and above, inserting multiple documents using collection.insert is just syntactic sugar for a BulkWrite. If you set the ordered flag to false, performance should be identical to an unordered bulk insert: db.collection.insert(<document array>,{ordered:false}) This operation will return a BulkWriteResult, … Read more
I was not satisfied with the highest rated answer here and so I’m providing a new one: I ended up using the node module ‘gridfs-stream’ (great documentation there!) which can be installed via npm. With it, and in combination with mongoose, it could look like this: var fs = require(‘fs’); var mongoose = require(“mongoose”); var … Read more