It is somewhat confusing since the names are similar, but the group() command is a different feature and implementation from the $group pipeline operator in the Aggregation Framework. The group() command, Aggregation Framework, and MapReduce are collectively aggregation features of MongoDB. There is some overlap in features, but I’ll attempt to explain the differences and …
You probably want to make a range query, for example, all items created after a given date: db.gpsdatas.find({“createdAt” : { $gte : new ISODate(“2012-01-12T20:15:31Z”) }}); I’m using $gte (greater than or equals), because this is often used for date-only queries, where the time component is 00:00:00. If you really want to find a date that …
You are correct that the “default” for specifying multiple field in a query is that each field serves as a conditional filter, and thus is an AND operation. You can perform MongoDB queries with an OR clause by using the $or operand which has the following syntax : db.col.find({$or:[clause1, clause2]}) Where each clause can be …
As asked, this is not possible. The server issue you linked to is still under “issues we’re not sure of”. MongoDB has some intelligence surrounding the use of arrays, and I think that’s part of the complexity surrounding such a feature. Take the following query db.foo.find({ ‘a.b’ : 4 } ). This query will match …
I think I got an answer. This is follow dsims answer and also from what I’ve seen in the documentation regarding logging. I have an initialize file (config/initializers/mongoid.rb) and in there I have: Mongoid.logger = Logger.new($stdout) Mongo::Logger.logger = Logger.new($stdout) It dumps out the mongo info the console. You probably want to change this for a …
MongoDB is complaining because you have an unrecognised pipeline stage specification “count”: { “$sum”: 1 } in your pipeline. Your original pipeline when formatted properly db.hashtag.aggregate([ { “$group”: { “_id”: { “year”: { “$year”: “$tweettime” }, “dayOfYear”: { “$dayOfYear”: “$tweettime” }, “interval”: { “$subtract”: [ { “$minute”: “$tweettime” }, { “$mod”: [{ “$minute”: “$tweettime”}, 15] …
if username Alex is unique, you can use next code: db.test.insert({username:”Alex”, tags: [‘C#’, ‘Java’, ‘C++’] }); db.test.aggregate( {$match: {username : “Alex”}}, {$unwind: “$tags”}, {$project: {count:{$add:1}}}, {$group: {_id: null, number: {$sum: “$count” }}} ); { “result” : [ { “_id” : null, “number” : 3 } ], “ok” : 1 }
You are beginning to think along the right lines here as you were headed in the right direction. Changing your SQL mindset, “distinct” is really just another way of writing a $group operation in either language. That means you have two group operations happening here and, in aggregation pipeline terms, two pipeline stages. Just with …
2017 Update Such a well put question deserves a modern response. The sort of array filtering requested can actually be done in modern MongoDB releases post 3.2 via simply $match and $project pipeline stages, much like the original plain query operation intends. db.accounts.aggregate([ { “$match”: { “email” : “john.doe@acme.com”, “groups”: { “$elemMatch”: { “name”: “group1”, …
With modern releases ( since MongoDB 3.4 ) you would use $switch, which is basically the counterpart to switch or case keywords in other language implementations: db.items.aggregate([ { “$project”: { “name”: 1, “customfield”: { “$switch”: { “branches”: [ { “case”: { “$eq”: [ “$field1”, “4” ] }, “then”: 30 }, { “case”: { “$eq”: [ …