aggregation-framework

问题 Per Mongo's latest $group documentation, there is a special optimization for $first: Optimization to Return the First Document of Each Group If a pipeline sorts and groups by the same field and the $group stage only uses the $first accumulator operator, consider adding an index on the grouped field which matches the sort order. In some cases, the $group stage can use the index to quickly find the first document of each group. It makes sense, since only the first entry in an ordered index

问题 I have two different collections (example below) methods & items . As for now, I'm using pre 3.6 vanilla aggregation query for $lookup : MongoPlayground Example { $lookup: { from: "items", localField: "reagents._id", foreignField: "_id", as: "reagent_items" } } The problem is that if I am using it, I miss quantity field (from methods.reagents embedded) during $lookup stage from original collection. For now, I return quantity right after lookup but as I heard, Mongo introduced from 3.6 a new

问题 I have two different collections (example below) methods & items . As for now, I'm using pre 3.6 vanilla aggregation query for $lookup : MongoPlayground Example { $lookup: { from: "items", localField: "reagents._id", foreignField: "_id", as: "reagent_items" } } The problem is that if I am using it, I miss quantity field (from methods.reagents embedded) during $lookup stage from original collection. For now, I return quantity right after lookup but as I heard, Mongo introduced from 3.6 a new

问题 I'm using MongoDB's aggregation. Using $in I'm checking if a value exists in an array or not, And I want to return the matched object from calificacion array into calificacion_usuario field. (my _id is unique in the array). I tried using $first" to return the current element. It's not working, not sure why & what to use. How can I do it? Sample Doc : { "cargo" : "Presidente", "calificacion" : [ { "_id" : "5e894ae6fa9fd23780bcf472", "estrellas" : 3 }, { "_id" : "5e895187fa9fd23780bcf478",

问题 Using MongoDB Charts, how can I chart cumulative growth? Using the _id value of a document which contains the information of when it was created, I'd like to chart the number of documents in my database over time. E.g., if in July 10 documents were created, and in August another 10 were created, then the chart should display 10 for July and 20 for August. It's easy to bin document creation dates per months (see below example), but I'd like to turn this into a cumulative growth chart. MongoDB

问题 Using MongoDB Charts, how can I chart cumulative growth? Using the _id value of a document which contains the information of when it was created, I'd like to chart the number of documents in my database over time. E.g., if in July 10 documents were created, and in August another 10 were created, then the chart should display 10 for July and 20 for August. It's easy to bin document creation dates per months (see below example), but I'd like to turn this into a cumulative growth chart. MongoDB

问题 I have this mongodb query db.getCollection('myCollection').aggregate( [{ $project: { length: { $strLenCP: "$prefix" } } }, { $sort: { length: -1 } }] ) that I want to use into a spring java project but I can't manage to write the correct java code (the sort is not the issue). I tried this Aggregation agg = newAggregation(project().andExpression("strLenCP(prefix)").as("prefixLength")); AggregationResults < RequestSettingsWithPrefixLength > results = mongoTemplate.aggregate(agg, RequestSettings

问题 { "no" : "2020921008981", "date" : ISODate("2020-04-01T05:19:02.263+0000"), "sale" : { "soldItems" : [ { "itemId" : "5b55ac7f0550de00210a3b24", "qty" : NumberInt(1), }, { "itemId" : "5b55ac7f0550de00210a3b25", "qty" : NumberInt(2), } ], "items" : [ { "_id" : ObjectId("5b55ac7f0550de00210a3b24"), unit :"KG" }, { "_id" : ObjectId("5b55ac7f0550de00210a3b25"), unit :"ML" } ] } } Desired output : { "no" : "2020921008981", "sale" : {} "qtyList" : "1 KG \n 2 ML" } In order to build itemQtyList

问题 I have a user document like: { _id: "s0m3Id", _skills: ["skill1", "skill2"], } Now I want to unwind this document by the _skills field and add a score for each skill. So my aggregate looks like: { '$unwind': {'path': '$_skills', 'preserveNullAndEmptyArrays': true}, }, { '$project': { '_skills': 'label': '$_skills', 'skill_score': 1 }, } }, Sometimes the _skills field can be empty, however in this case I still want the user document to flow through the aggregation - hence the

问题 I have the following document structure { "_id" : 1, "prices" : { "100" : [ 5.67, . . 1.7, ], "101" : [ 4.67, . . 1.4, }, "v" : 2 } We need to get the last value from each of the fields "100" and "101", e.g 1.7 & 1.4, using mongodb v3.0.2. Currently we are loading the whole document and then getting the required values in the application. It has become quite a bottleneck as each document may be ~1MB, which for 100s of documents is adding up. We are hoping there is a suitable feature of