mongodb-query

问题 How to get the most common distinct values of a key in query results. Consider a collection 'collectionSample' { name : 'a', value: 10, word : 'baz' }, { name : 'a', value: 65, word : 'bar' }, { name : 'a', value: 3, word : 'foo' }, { name : 'b', value: 110, word : 'bar' }, { name : 'b', value: 256, word : 'baz' } Here I want to find the mode of key 'name', that is the most repeated distinct 'name'. The result I'm hoping to get is like {'most_common_distinct_val':a} //since a is count 3 and b

问题 If I have a mongodb collection users like this: { "_id": 1, "name": { "first" : "John", "last" :"Backus" }, } How do I retrieve name.first from this without providing _id or any other reference. Also, is it possible that pulling just the `name^ can give me the array of embedded keys (first and last in this case)? How can that be done? db.users.find({"name.first"}) didn't work for me, I got a: SyntaxError "missing: after property id (shell):1 回答1: The first argument to find() is the query

问题 I have the following scenario: One of my mongo collections has documents in the following format: user: "test", tracks: [{artist: "A", ...}, {artist: "B", ...}, ..., { artist: "N", ...}] I would like to extract all the tracks, whose artists are in a given array arr . For that purpose I'm using the following query (which works fine). collection.find({ tracks: { $elemMatch: { artist: { $in: arr }}}}) However, now I would like to modify the query so that it returns only those documents in the

问题 Learning MongoDB for the past two days and I am trying to aggregate three collections but unable to achieve it Below are the four collection maintaining in the database university { "_id" : "5834ecf7432d92675bde9d82", "name": "NIFT" } college { "_id" : "5834ecf7432d92675bde9d83", "name": "NIFT Hyderabad", "university_id":"5834ecf7432d92675bde9d82" } departments { "_id" : "5834ecf7432d92675bde9d84", "department_name": "Fashion Technology", "college_id" : "5834ecf7432d92675bde9d83" }, { "_id" :

问题 I'm updating multiple elements in mongodb. Is it possible to return the number of affected objects? 回答1: Use getLastError. The n key will contain the number of updated documents > db.count.update({x : 1}, {$inc : {x : 1}}, false, true) > db.runCommand({getLastError : 1}) { "err" : null, "updatedExisting" : true, "n" : 5, "ok" : true } Note that this runs the command "getLastError" which returns the number of rows after the update command has completed. Database commands are listed here. 来源：

问题 In my small ExpressJS app, I have a Question model which was defined like that var mongoose = require('mongoose'), Schema = mongoose.Schema; /** * Question Schema */ var Question = new Schema({ title: { type: String, default: '', trim: true, required: 'Title cannot be blank' }, content: { type: String, default: '', trim: true }, created: { type: Date, default: Date.now }, updated: { type: Date, default: Date.now }, author: { type: Schema.ObjectId, ref: 'User', require: true }, answers : [{

问题 Document Sample: { "_id" : ObjectId("53329dfgg43771e49538b4567"), "u" : { "_id" : ObjectId("532a435gs4c771edb168c1bd7"), "n" : "Salman khan", "e" : "salman@gmail.com" }, "ps" : 0, "os" : 1, "rs" : 0, "cd" : 1395685800, "ud" : 0 } Query: db.collectiontmp.aggregate([ {$match: {os:1}}, {$project : { name:{$toUpper:"$u.e"} , _id:0 } }, {$group: { _id: "$u._id",total: {$sum:1} }}, {$sort: {total: -1}}, { $limit: 10 } ]); I need following things from the above query: Group by u._id Returns total

问题 Created a new mLab account and created a database as per the steps here http://docs.mlab.com/#create-sub . Trying to connect to the database using mongo shell and mongoose Node.js module but I see the 'Authentication Failed' errorin both cases. In Mongo shell the command is, I have double checked the credentials mongo ds012345.mlab.com:56789/dbname -u dbuser -p dbpassword Error: MongoError: authentication fail at Function.MongoError.create (E:\Gatsby\notmongoose\node_modules\mongodb-core\lib

问题 I want to achieve $sum with $cond by having $or on property: db.collectionName.aggregate( { "$group": { "_id":'$created_at', "count": {"$sum": 1}, "count_failure": { "$sum": { "$cond": [ { "$id": { "$in": [ 0,100,101,102,103,104,105 ] } }, 1, 0 ] } } } } ) But error says: Invalid operator "$id" What's wrong with syntax? Or I am writing query wrongly. Currently I am achieving this by: db.collectionName.aggregate( { "$group": { "_id":'$created_at', "count": {"$sum": 1}, "count_failure": { "$sum

问题 I have to write a complex mongo query using java but am not able to do it. The mongo query looks like this: db.video.findOne( { $or: [ { key1: { $in : [764] } }, { key2: {$in : [list2] } }, { $and [ { key2 : 3}, {key4:67} ] } ] }) I have to write the above query using the QueryBuilder class. In what way can I do it? Thanks 回答1: Using QueryBuilder your query should look like this DBObject query = QueryBuilder.start().or( QueryBuilder.start("key1").in(764).get(), QueryBuilder.start("key2").in