MongoDB的汇聚$组，然后$推对象

Question

，这是我的数据：

> db.bookmarks.find({"userId" : "56b9b74bf976ab70ff6b9999"}).pretty() 
{ 
    "_id" : ObjectId("56c2210fee4a33579f4202dd"), 
    "userId" : "56b9b74bf976ab70ff6b9999", 
    "items" : [ 
     { 
      "itemId" : "28", 
      "timestamp" : "2016-02-12T18:07:28Z" 
     }, 
     { 
      "itemId" : "29", 
      "timestamp" : "2016-02-12T18:07:29Z" 
     }, 
     { 
      "itemId" : "30", 
      "timestamp" : "2016-02-12T18:07:30Z" 
     }, 
     { 
      "itemId" : "31", 
      "timestamp" : "2016-02-12T18:07:31Z" 
     }, 
     { 
      "itemId" : "32", 
      "timestamp" : "2016-02-12T18:07:32Z" 
     }, 
     { 
      "itemId" : "33", 
      "timestamp" : "2016-02-12T18:07:33Z" 
     }, 
     { 
      "itemId" : "34", 
      "timestamp" : "2016-02-12T18:07:34Z" 
     } 
    ] 
} 

我想有像（其实我希望_id能成为用户id太）：

{ 
    "_id" : "56b9b74bf976ab70ff6b9999", 
    "items" : [ 
     { "itemId": "32", "timestamp": "2016-02-12T18:07:32Z" }, 
     { "itemId": "31", "timestamp": "2016-02-12T18:07:31Z" }, 
     { "itemId": "30", "timestamp": "2016-02-12T18:07:30Z" } 
    ] 
} 

我现在拥有的一切：

> db.bookmarks.aggregate(
...  { $match: { "userId" : "56b9b74bf976ab70ff6b9999" } }, 
...  { $unwind: '$items' }, 
...  { $sort: { 'items.timestamp': -1} }, 
...  { $skip: 2 }, 
...  { $limit: 3}, 
...  { $group: { '_id': '$userId' , items: { $push: '$items.itemId' } } } 
...).pretty() 
{ "_id" : "56b9b74bf976ab70ff6b9999", "items" : [ "32", "31", "30" ] } 

我试图读取蒙戈的文件，并找出我可以$推，但不知何故，我不能找到一种方法，这样的推对象，它在整个对象的任何地方都没有定义。我想要时间戳也..但我不知道我应该如何修改$组（或其他人??）这样做。感谢您的帮助！

Answer 1

此代码，这是我在MongoDB中3.2.1测试壳，应该给你你想要的输出格式：

> db.bookmarks.aggregate( 
{ "$match" : { "userId" : "Ursula" } }, 
{ "$unwind" : "$items" }, 
{ "$sort" : { "items.timestamp" : -1 } }, 
{ "$skip" : 2 }, 
{ "$limit" : 3 }, 
{ "$group" : { "_id" : "$userId", items: { "$push" : { "myPlace" : "$items.itemId", "myStamp" : "$items.timestamp" } } } } ).pretty() 

运行上面会产生这样的输出：

{ 
    "_id" : "Ursula", 
    "items" : [ 
     { 
      "myPlace" : "52", 
      "myStamp" : ISODate("2016-02-13T18:07:32Z") 
     }, 
     { 
      "myPlace" : "51", 
      "myStamp" : ISODate("2016-02-13T18:07:31Z") 
     }, 
     { 
      "myPlace" : "50", 
      "myStamp" : ISODate("2016-02-13T18:07:30Z") 
     } 
    ] 
} 

在MongoDB 3.2.x版中，您还可以在聚合管道的最后阶段使用$ out操作符，并将聚合查询的输出写入集合。下面是我使用的代码：

> db.bookmarks.aggregate( 
{ "$match" : { "userId" : "Ursula" } }, 
{ "$unwind" : "$items" }, 
{ "$sort" : { "items.timestamp" : -1 } }, 
{ "$skip" : 2 }, 
{ "$limit" : 3 }, 
{ "$group" : { "_id" : "$userId", items: { "$push" : { "myPlace" : "$items.itemId", "myStamp" : "$items.timestamp" } } } }, 
{ "$out" : "ursula" }) 

这给了我一个名为 “邦女郎” 集合：

> show collections 
ursula 

，我可以查询该集合：

> db.ursula.find().pretty() 
{ 
    "_id" : "Ursula", 
    "items" : [ 
     { 
      "myPlace" : "52", 
      "myStamp" : ISODate("2016-02-13T18:07:32Z") 
     }, 
     { 
      "myPlace" : "51", 
      "myStamp" : ISODate("2016-02-13T18:07:31Z") 
     }, 
     { 
      "myPlace" : "50", 
      "myStamp" : ISODate("2016-02-13T18:07:30Z") 
     } 
    ] 
} 
> 

所有的最后，这是我在聚合查询中使用的输入文档。您可以将此文档与我如何对聚合查询进行编码以查看构建新项目数组的方式进行比较。

> db.bookmarks.find({ "userId" : "Ursula" }).pretty() 
{ 
    "_id" : ObjectId("56c240ed55f2f6004dc3b25c"), 
    "userId" : "Ursula", 
    "items" : [ 
     { 
      "itemId" : "48", 
      "timestamp" : ISODate("2016-02-13T18:07:28Z") 
     }, 
     { 
      "itemId" : "49", 
      "timestamp" : ISODate("2016-02-13T18:07:29Z") 
     }, 
     { 
      "itemId" : "50", 
      "timestamp" : ISODate("2016-02-13T18:07:30Z") 
     }, 
     { 
      "itemId" : "51", 
      "timestamp" : ISODate("2016-02-13T18:07:31Z") 
     }, 
     { 
      "itemId" : "52", 
      "timestamp" : ISODate("2016-02-13T18:07:32Z") 
     }, 
     { 
      "itemId" : "53", 
      "timestamp" : ISODate("2016-02-13T18:07:33Z") 
     }, 
     { 
      "itemId" : "54", 
      "timestamp" : ISODate("2016-02-13T18:07:34Z") 
     } 
    ] 
}