这确实是一个棘手的问题。这里的基础是，
.populate()当然也不是“用虚拟机填充”，并不是为了像您期望的那样工作。问题说明
本质上，实质上
.populate()是向MongoDB发出的另一个查询，以检索相关数据。为此，它基本上发出一个查询，
$in其中包含要匹配的目标的所有“相关字段”值。
“问题4321”的核心是，具有这样的选项，
"sort"而
"limit"需要提供此类
$in参数的实际查询实际上是一条
.aggregate()语句，该语句将能够
“获取
n为每个键分组的最后结果”。这实际上不是Mongoose当前发布给MongoDB的东西，这时
n按可用 *** 作对项目进行分组也不现实。
您可以
.aggregate()手动解决该问题，如提供的清单末尾所示，但是当然实际上仅在少数情况下。
// Get latest transactions for each master Transaction.aggregate([ { '$match': { '_asset': { '$in': masters.map(m => m._id) } }}, { '$sort': { '_asset': 1, 'createdAt': -1 } }, { '$group': { '_id': '$_asset', 'amount': { '$first': '$amount' }, 'createdAt': { '$first': '$createdAt' }, 'updatedAt': { '$first': '$updatedAt' }, 'did': { '$first': '$_id' } }}, { '$project': { '_id': '$did', '_asset': '$_id', 'amount': 1, 'createdAt': 1, 'updatedAt': 1 }} ])这不是很好，也不是一个真正有效的解决方案，但是比其他类似的替代方案要好。我相信，尽管还有更好的方法。
更好的解决方案对于您这里的情况，我会怀疑很多类似的情况，由于所产生的数组的潜在大小，您甚至不想在父文档中包括“完整”事务列表作为参考。这种“反模式”通常是“虚拟人群”所使用的，实际上
$lookup是要避免的。
但是，在您的特定用例 “获取最新交易”中 ，这两个都不是可行的解决方案。因为两者本质上都需要查看“所有”交易，然后才
n从中检索结果。
因此，这里的“最新”或实际上是“最新”的情况实际上是退回到“嵌入”（至少是引用）的“有限数量”，以提供可行的解决方案。因此，提案就是要做到这一点，并
"recent"在父公司内部保留交易清单。这为您提供了所包含场景中的文档，如下所示：
{ "_id" : ObjectId("5959e34adf833e1451a32661"), "__v" : 0, "name" : "One", "recent" : [ ObjectId("5959e34bdf833e1451a32676"), ObjectId("5959e34bdf833e1451a32674"), ObjectId("5959e34bdf833e1451a32672"), ObjectId("5959e34bdf833e1451a32670"), ObjectId("5959e34bdf833e1451a3266e") ]}在此请注意，这些并非“全部”相关交易，而仅是“最新”交易。关键是仅保留一个适合此目的的“小”列表。
这样，您可以直接查询“父级”，而仅查询
$slice包含在
"recent"项中的数组。在清单中，我这样做是：
Master.find().select({ 'recent': { '$slice': 1 } })这将从阵列中返回“最新”条目，而无需对服务器进行任何其他查询。在这种情况下，它是“最新的”，因为相反，我们在写入
"transactions"包含所有内容的集合的同时，将项目“前置”到了该数组中：
Transaction.create({ _asset: master._id, amount: data.amount }) .then(transaction => Master.update( { _id: transaction._asset }, { "$push": { "recent": { "$each": [transaction._id], "$position": 0, "$slice": 5 } }} )$push父
$position级数组中的关键元素在数组的开头用前缀“
preprend”进行了修改，因此“第一”项始终是要添加的与父级相关的“最新”事务。
然后在
$slice这里使用修饰符将
"recent"数组保持在限制
n项目数量。因此，当添加较新的项目时，“最旧的”项目将“从”列表中删除。
然后，这里还有另一个实际目的，即在分页方案中列出“主”和“事务”时，第一个请求可以
"recent"直接使用该数组。然后，对新“页面”的其他请求可以简单地通过过滤掉
"recent"数组中包含的项目，
$nin并使用常规
.skip()和/
.limit()或备用“范围”分页实践来检索结果的每个“页面”。
为了完整地演示所有概念，请参见下面的清单和所有生成的结果。
演示清单：
const async = require('async'), mongoose = require('mongoose'), Schema = mongoose.Schema;mongoose.set('debug',true);mongoose.Promise = global.Promise;mongoose.connect('mongodb://localhost/prepend');const transactionSchema = new Schema({ _asset: { type: Schema.Types.ObjectId, ref: 'Master' }, amount: Number},{ timestamps: { createdAt: 'createdAt' }});const Transaction = mongoose.model('Transaction', transactionSchema);const masterSchema = new Schema({ name: String, recent: [{ type: Schema.Types.ObjectId, ref: 'Transaction' }]});masterSchema.virtual('transactions', { ref: 'Transaction', localField: '_id', foreignField: '_asset', justOne: false});const Master = mongoose.model('Master', masterSchema);function log(data) { console.log(JSON.stringify(data, undefined, 2))}async.series( [ // Clean data (callback) => async.each(mongoose.models,(model,callback) => model.remove({},callback),callback), // Create Masters (callback) => Master.insertMany(['One','Two'].map( name => ({ name })),callback), // Add 10 transactions to each master (callback) => async.each(['One','Two'],(name,callback) => async.eachSeries( Array.apply(null,Array(10)).map((e,i) => ({ name, amount: i+1 })), (data,callback) => { Master.findOne({ name: data.name }) .then(master => Transaction.create({ _asset: master._id, amount: data.amount }) ) .then(transaction => Master.update( { _id: transaction._asset }, { "$push": { "recent": {"$each": [transaction._id],"$position": 0,"$slice": 5 } }} ) ) .then(res => callback()) .catch(callback) }, callback ), callback), // Show populated recent 1 entry only (callback) => Master.find().select({ 'recent': { '$slice': 1 } }) .populate('recent').exec((err,results) => { if (err) callback(err); log(results); callback(); }), // Populate recent - page 1 then fetch next page (callback) => async.waterfall( [ (callback) => Master.findOne({ name: 'One' }).populate('recent') .lean() .exec((err,master) => { if (err) callback(err); log(master); callback(null,{ _asset: master._id, exclude: master.recent.map( r => r._id ) }); }), (options,callback) => Transaction.find({ _asset: options._asset, _id: { '$nin': options.exclude } }).sort({ 'createdAt': -1 }).limit(5) .exec((err,transactions) => { if (err) callback(err); log(transactions) callback(); }) ], callback ), // Issue 4321 - Fix - Manual populate with aggregate (callback) => Master.find().select('-recent').exec() .then(masters => { // Get latest transactions for each master Transaction.aggregate([ { '$match': { '_asset': { '$in': masters.map(m => m._id) } }}, { '$sort': { '_asset': 1, 'createdAt': -1 } }, { '$group': { '_id': '$_asset', 'amount': { '$first': '$amount' }, 'createdAt': { '$first': '$createdAt' }, 'updatedAt': { '$first': '$updatedAt' }, 'did': { '$first': '$_id' } }}, { '$project': { '_id': '$did', '_asset': '$_id', 'amount': 1, 'createdAt': 1, 'updatedAt': 1 }} ]).exec((err,transactions) => { // Map latest transactions to master masters = masters.map( m => Object.assign( m.toObject(), { transactions: transactions.filter( t => t._asset.toHexString() === m._id.toHexString() ) } ) ); log(masters); callback(); }) }).catch(callback) ], (err) => { if (err) throw err; mongoose.disconnect(); });示范输出
Mongoose: transactions.remove({}, {})Mongoose: masters.remove({}, {})Mongoose: masters.insertMany([ { __v: 0, name: 'One', _id: 5959e34adf833e1451a32661, recent: [] }, { __v: 0, name: 'Two', _id: 5959e34adf833e1451a32662, recent: [] } ], null)Mongoose: masters.findOne({ name: 'One' }, { fields: {} })Mongoose: masters.findOne({ name: 'Two' }, { fields: {} })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:14 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:14 GMT"), _asset: ObjectId("5959e34adf833e1451a32662"), amount: 1, _id: ObjectId("5959e34adf833e1451a32663"), __v: 0 })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32661"), amount: 1, _id: ObjectId("5959e34adf833e1451a32664"), __v: 0 })Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32661") }, { '$push': { recent: { '$each': [ ObjectId("5959e34adf833e1451a32664") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32662") }, { '$push': { recent: { '$each': [ ObjectId("5959e34adf833e1451a32663") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.findOne({ name: 'One' }, { fields: {} })Mongoose: masters.findOne({ name: 'Two' }, { fields: {} })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32662"), amount: 2, _id: ObjectId("5959e34bdf833e1451a32665"), __v: 0 })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32661"), amount: 2, _id: ObjectId("5959e34bdf833e1451a32666"), __v: 0 })Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32661") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a32666") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32662") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a32665") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.findOne({ name: 'One' }, { fields: {} })Mongoose: masters.findOne({ name: 'Two' }, { fields: {} })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32662"), amount: 3, _id: ObjectId("5959e34bdf833e1451a32667"), __v: 0 })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32661"), amount: 3, _id: ObjectId("5959e34bdf833e1451a32668"), __v: 0 })Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32661") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a32668") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32662") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a32667") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.findOne({ name: 'One' }, { fields: {} })Mongoose: masters.findOne({ name: 'Two' }, { fields: {} })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32662"), amount: 4, _id: ObjectId("5959e34bdf833e1451a32669"), __v: 0 })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32661"), amount: 4, _id: ObjectId("5959e34bdf833e1451a3266a"), __v: 0 })Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32661") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a3266a") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32662") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a32669") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.findOne({ name: 'One' }, { fields: {} })Mongoose: masters.findOne({ name: 'Two' }, { fields: {} })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32662"), amount: 5, _id: ObjectId("5959e34bdf833e1451a3266b"), __v: 0 })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32661"), amount: 5, _id: ObjectId("5959e34bdf833e1451a3266c"), __v: 0 })Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32661") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a3266c") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32662") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a3266b") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.findOne({ name: 'One' }, { fields: {} })Mongoose: masters.findOne({ name: 'Two' }, { fields: {} })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32662"), amount: 6, _id: ObjectId("5959e34bdf833e1451a3266d"), __v: 0 })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32661"), amount: 6, _id: ObjectId("5959e34bdf833e1451a3266e"), __v: 0 })Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32661") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a3266e") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32662") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a3266d") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.findOne({ name: 'One' }, { fields: {} })Mongoose: masters.findOne({ name: 'Two' }, { fields: {} })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32662"), amount: 7, _id: ObjectId("5959e34bdf833e1451a3266f"), __v: 0 })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32661"), amount: 7, _id: ObjectId("5959e34bdf833e1451a32670"), __v: 0 })Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32661") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a32670") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32662") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a3266f") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.findOne({ name: 'One' }, { fields: {} })Mongoose: masters.findOne({ name: 'Two' }, { fields: {} })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32662"), amount: 8, _id: ObjectId("5959e34bdf833e1451a32671"), __v: 0 })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32661"), amount: 8, _id: ObjectId("5959e34bdf833e1451a32672"), __v: 0 })Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32661") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a32672") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32662") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a32671") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.findOne({ name: 'One' }, { fields: {} })Mongoose: masters.findOne({ name: 'Two' }, { fields: {} })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32662"), amount: 9, _id: ObjectId("5959e34bdf833e1451a32673"), __v: 0 })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32661"), amount: 9, _id: ObjectId("5959e34bdf833e1451a32674"), __v: 0 })Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32661") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a32674") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32662") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a32673") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.findOne({ name: 'One' }, { fields: {} })Mongoose: masters.findOne({ name: 'Two' }, { fields: {} })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32662"), amount: 10, _id: ObjectId("5959e34bdf833e1451a32675"), __v: 0 })Mongoose: transactions.insert({ updatedAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), createdAt: new Date("Mon, 03 Jul 2017 06:25:15 GMT"), _asset: ObjectId("5959e34adf833e1451a32661"), amount: 10, _id: ObjectId("5959e34bdf833e1451a32676"), __v: 0 })Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32661") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a32676") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.update({ _id: ObjectId("5959e34adf833e1451a32662") }, { '$push': { recent: { '$each': [ ObjectId("5959e34bdf833e1451a32675") ], '$slice': 5, '$position': 0 } } }, {})Mongoose: masters.find({}, { fields: { recent: { '$slice': 1 } } })Mongoose: transactions.find({ _id: { '$in': [ ObjectId("5959e34bdf833e1451a32676"), ObjectId("5959e34bdf833e1451a32675") ] } }, { fields: {} })[ { "_id": "5959e34adf833e1451a32661", "__v": 0, "name": "One", "recent": [ { "_id": "5959e34bdf833e1451a32676", "updatedAt": "2017-07-03T06:25:15.282Z", "createdAt": "2017-07-03T06:25:15.282Z", "_asset": "5959e34adf833e1451a32661", "amount": 10, "__v": 0 } ] }, { "_id": "5959e34adf833e1451a32662", "__v": 0, "name": "Two", "recent": [ { "_id": "5959e34bdf833e1451a32675", "updatedAt": "2017-07-03T06:25:15.280Z", "createdAt": "2017-07-03T06:25:15.280Z", "_asset": "5959e34adf833e1451a32662", "amount": 10, "__v": 0 } ] }]Mongoose: masters.findOne({ name: 'One' }, { fields: {} })Mongoose: transactions.find({ _id: { '$in': [ ObjectId("5959e34bdf833e1451a32676"), ObjectId("5959e34bdf833e1451a32674"), ObjectId("5959e34bdf833e1451a32672"), ObjectId("5959e34bdf833e1451a32670"), ObjectId("5959e34bdf833e1451a3266e") ] } }, { fields: {} }){ "_id": "5959e34adf833e1451a32661", "__v": 0, "name": "One", "recent": [ { "_id": "5959e34bdf833e1451a32676", "updatedAt": "2017-07-03T06:25:15.282Z", "createdAt": "2017-07-03T06:25:15.282Z", "_asset": "5959e34adf833e1451a32661", "amount": 10, "__v": 0 }, { "_id": "5959e34bdf833e1451a32674", "updatedAt": "2017-07-03T06:25:15.264Z", "createdAt": "2017-07-03T06:25:15.264Z", "_asset": "5959e34adf833e1451a32661", "amount": 9, "__v": 0 }, { "_id": "5959e34bdf833e1451a32672", "updatedAt": "2017-07-03T06:25:15.216Z", "createdAt": "2017-07-03T06:25:15.216Z", "_asset": "5959e34adf833e1451a32661", "amount": 8, "__v": 0 }, { "_id": "5959e34bdf833e1451a32670", "updatedAt": "2017-07-03T06:25:15.195Z", "createdAt": "2017-07-03T06:25:15.195Z", "_asset": "5959e34adf833e1451a32661", "amount": 7, "__v": 0 }, { "_id": "5959e34bdf833e1451a3266e", "updatedAt": "2017-07-03T06:25:15.180Z", "createdAt": "2017-07-03T06:25:15.180Z", "_asset": "5959e34adf833e1451a32661", "amount": 6, "__v": 0 } ]}Mongoose: transactions.find({ _id: { '$nin': [ ObjectId("5959e34bdf833e1451a32676"), ObjectId("5959e34bdf833e1451a32674"), ObjectId("5959e34bdf833e1451a32672"), ObjectId("5959e34bdf833e1451a32670"), ObjectId("5959e34bdf833e1451a3266e") ] }, _asset: ObjectId("5959e34adf833e1451a32661") }, { sort: { createdAt: -1 }, limit: 5, fields: {} })[ { "_id": "5959e34bdf833e1451a3266c", "updatedAt": "2017-07-03T06:25:15.164Z", "createdAt": "2017-07-03T06:25:15.164Z", "_asset": "5959e34adf833e1451a32661", "amount": 5, "__v": 0 }, { "_id": "5959e34bdf833e1451a3266a", "updatedAt": "2017-07-03T06:25:15.135Z", "createdAt": "2017-07-03T06:25:15.135Z", "_asset": "5959e34adf833e1451a32661", "amount": 4, "__v": 0 }, { "_id": "5959e34bdf833e1451a32668", "updatedAt": "2017-07-03T06:25:15.080Z", "createdAt": "2017-07-03T06:25:15.080Z", "_asset": "5959e34adf833e1451a32661", "amount": 3, "__v": 0 }, { "_id": "5959e34bdf833e1451a32666", "updatedAt": "2017-07-03T06:25:15.039Z", "createdAt": "2017-07-03T06:25:15.039Z", "_asset": "5959e34adf833e1451a32661", "amount": 2, "__v": 0 }, { "_id": "5959e34adf833e1451a32664", "updatedAt": "2017-07-03T06:25:15.009Z", "createdAt": "2017-07-03T06:25:15.009Z", "_asset": "5959e34adf833e1451a32661", "amount": 1, "__v": 0 }]Mongoose: masters.find({}, { fields: { recent: 0 } })Mongoose: transactions.aggregate([ { '$match': { _asset: { '$in': [ 5959e34adf833e1451a32661, 5959e34adf833e1451a32662 ] } } }, { '$sort': { _asset: 1, createdAt: -1 } }, { '$group': { _id: '$_asset', amount: { '$first': '$amount' }, createdAt: { '$first': '$createdAt' }, updatedAt: { '$first': '$updatedAt' }, did: { '$first': '$_id' } } }, { '$project': { _id: '$did', _asset: '$_id', amount: 1, createdAt: 1, updatedAt: 1 } } ], {})[ { "_id": "5959e34adf833e1451a32661", "__v": 0, "name": "One", "transactions": [ { "amount": 10, "createdAt": "2017-07-03T06:25:15.282Z", "updatedAt": "2017-07-03T06:25:15.282Z", "_id": "5959e34bdf833e1451a32676", "_asset": "5959e34adf833e1451a32661" } ] }, { "_id": "5959e34adf833e1451a32662", "__v": 0, "name": "Two", "transactions": [ { "amount": 10, "createdAt": "2017-07-03T06:25:15.280Z", "updatedAt": "2017-07-03T06:25:15.280Z", "_id": "5959e34bdf833e1451a32675", "_asset": "5959e34adf833e1451a32662" } ] }]欢迎分享，转载请注明来源：内存溢出
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