在mongodb中不显示$ Sum输出

我编码了一个简单的查询$总，但它似乎并没有显示我的输出我想要的。 它应该显示所有machine_unit的平均air_temperature。

var express = require('express'); var app = express(); var mongojs = require('mongojs'); var db = mongojs('meibanlist', ['meibanlist']); var bodyParser = require('body-parser'); app.use(express.static(__dirname + '/public')); app.use(bodyParser.json()); app.get('/meibanlist', function (req, res) { console.log('I received a GET request'); db.meibanlist.find(function (err, docs) { console.log(docs); res.json(docs); }); }); app.post('/meibanlist', function (req, res) { console.log(req.body); db.meibanlist.insert(req.body, function(err, doc) { res.json(doc); }); }); app.delete('/meibanlist/:id', function (req, res) { var id = req.params.id; console.log(id); db.meibanlist.remove({_id: mongojs.ObjectId(id)}, function (err, doc) { res.json(doc); }); }); app.get('/meibanlist/:id', function (req, res) { var id = req.params.id; console.log(id); db.meibanlist.findOne({_id: mongojs.ObjectId(id)}, function (err, doc) { res.json(doc); }); }); app.put('/meibanlist/:id', function (req, res) { var id = req.params.id; console.log(req.body.machine_unit); db.meibanlist.findAndModify({ query: {_id: mongojs.ObjectId(id)}, update: {$set: {machine_unit: req.body.machine_unit, air_temperature: req.body.air_temperature, water_temperature: req.body.water_temperature, heat_temperature: req.body.heat_temperature, room_temperature: req.body.room_temperature, date: req.body.date, time: req.body.time}}, new: true}, function (err, doc) { res.json(doc); } ); }); 

///这是所有的错误

 db.meibanlist.aggregate([{$project:{ "Average": { $avg: ["$air_temperature"] }}}], function(err, meibanlist){ if (err || !meibanlist) console.log ("Record not found"); else meibanlist.forEach (function(machine_unit){ console.log(machine_unit); }); }); app.listen(3000); console.log("Server running on port 3000"); 

Answer 1

为了得到所有machine_unit的平均air_temperature，你可以用下面的方法来完成，假设你的machine_unit是唯一的。

 db.meibanlist.aggregate({$group: {_id: null,"average": {$avg: "$air_temperature"}}}).pretty() 

如果你想分组machine_unit，并获得平均air_temperature的基础上machine_unit你可以做到这一点，我遵循

 db.meibanlist.aggregate({$group: {_id: "$machine_unit","average": {$avg: "$air_temperature"}}}).pretty() 

如果数组存储在air_temperature中，并且想要投影并获得每个logging的air_temperature的平均值。 你可以通过以下方式实现它：

 db.meibanlist.aggregate({"$project": {"average": {$avg: "$air_temperature"}}}).pretty()