aggregation-framework

问题 I need a way to change the elements of an array field to values of a dict with a single attribute. I don't have to write the result back into my table. I just have to read it that way. My table has rows like this : {a: 1, b:[ {...}, ..., {...} ], c: 2} I need a query that returns each row rewritten like this : {a: 1, b: [ {foo: { ... }}, ..., {foo: {...}} ], c: 2} In other words, each element of b becomes a dict with a single attribute, foo . This feels like a job for $project or $replaceRoot

问题 Let's say a have a simple document: { array: ["a", "b", "c", "d"] } How to modify the second value in aggregation ? With update it is very simple: db.collection.updateOne({}, { $set: { "array.1": "B" } } ) gives: { array: ["a", "B", "c", "d"] } In aggregation framework you can use this one: db.collection.aggregate([ { $set: { "array": { $map: { input: "$array", in: { $cond: { if: { $eq: [{ $indexOfArray: ["$array", "$$this"] }, 1] }, then: "B", else: "$$this" } } } } } } ]) However, this

问题 I have two collections. articles and bookmarks. articles { _id: "5faa889ade5e0a6326a873d3", name: "article 1" }, { _id: "5faa889ade5e0a6326a873d", name: "article 2" } bookmarks { _id: "5faa889ade5e0a6326a873d1", user_id: "5fc7b50da483a66a86aa7e9e", model_id: "5faa889ade5e0a6326a873d3" } I want to join article with bookmark. if user bookmarked a article. what i have tried const aggregate = await Articles.aggregate([{ $lookup: { from: "categories", localField: "category_id", foreignField: "_id"

问题 I have a model Entry to which includes details of a hospital at a particular time. The data looks like this: { "_id": "5ef9c7337874820008c1a026", "date": 1593427763640, //... some data "hospital": { "_id": "5ef8d06630c364000840bb6d", "name": "City Hospital", //... some data }, } I want to get the last query of each day grouped by the hospital ID. In MySQL, it can be achieved using INNER JOIN. How can I do it using MongoDB? 回答1: Given a day, calculate start and end of a day. This is to be used

问题 I have 2 collections, the first storing the animes watched by each user, their status etc: const listSchema = mongoose.Schema({ user: { type: Schema.Types.ObjectId, ref: 'user' }, animes: [{ _id: false, anime: { type: Schema.Types.ObjectId, ref: 'anime', unique: true }, status: String, episodes: Number, rating: Number }] }); and the second storing all animes and the relevant information. I want to show that second collection but adding status and episodes fields that are filled from the list

问题 I have 2 collections, the first storing the animes watched by each user, their status etc: const listSchema = mongoose.Schema({ user: { type: Schema.Types.ObjectId, ref: 'user' }, animes: [{ _id: false, anime: { type: Schema.Types.ObjectId, ref: 'anime', unique: true }, status: String, episodes: Number, rating: Number }] }); and the second storing all animes and the relevant information. I want to show that second collection but adding status and episodes fields that are filled from the list

问题 I'm linking two objects in one query and use aggregate function for it. Some data is localized and I'm using a solution from here to get data for specified locale. I am struggling to do the same with data from the linked object (rooms). Specifically, list data for given locale from the roomDetails. Please take a look at the Mongo playground 回答1: You just need to add filter in your second $addFields stage that you are filtering roomTypes and rest of the stages would be same, just highlighted

问题 I'm linking two objects in one query and use aggregate function for it. Some data is localized and I'm using a solution from here to get data for specified locale. I am struggling to do the same with data from the linked object (rooms). Specifically, list data for given locale from the roomDetails. Please take a look at the Mongo playground 回答1: You just need to add filter in your second $addFields stage that you are filtering roomTypes and rest of the stages would be same, just highlighted

问题 I'm linking two objects in one query and use aggregate function for it. Some data is localized and I'm using a solution from here to get data for specified locale. I am struggling to do the same with data from the linked object (rooms). Specifically, list data for given locale from the roomDetails. Please take a look at the Mongo playground 回答1: You just need to add filter in your second $addFields stage that you are filtering roomTypes and rest of the stages would be same, just highlighted

问题 I have collection database with 10 000 000 call records. I want to compare call usage of previous month to next month. Example of collection document { "_id" : ObjectId("54ed74d76c68d23af73e230a"), "msisdn" : "9818441000", "callType" : "ISD" "duration" : 10.109999656677246, "charges" : 200, "traffic" : "Voice", "Date" : ISODate("2014-01-05T19:51:01.928Z") } { "_id" : ObjectId("54ed74d76c68d23af73e230b"), "msisdn" : "9818843796", "callType" : "Local", "duration" : 1, "charges" : 150, "traffic"