如何查询以获取Mongoose中的最后更新日期

Question

我有这个mongodb集合。有两个file1.pkg与lastUpdate日期不同。

{ 
    "_id" : ObjectId("550286416fee741b0379c2d8"), 
    "lastUpdate" : ISODate("2015-03-12T16:00:00.000Z"), 
    "file" : "file1.pkg", 
    "idBook" : "54f6d1d8c239491400aa495e", 
    "idUser" : "54c83f37e2e315bfbb43e98a" 
}, 
{ 
    "_id" : ObjectId("450286416fee741e0379c2d8"), 
    "lastUpdate" : ISODate("2015-03-10T16:00:00.000Z"), 
    "file" : "file1.pkg", 
    "idBook" : "54f6d1d8c239491400aa495e", 
    "idUser" : "54c83f37e2e315bfbb43e98a", 
}, 
{ 
    "_id" : ObjectId("560286416fee741b0379c24d"), 
    "lastUpdate" : ISODate("2015-03-12T16:00:00.000Z"), 
    "file" : "file2.pkg", 
    "idBook" : "54f6d1d8c239491400aa495e", 
    "idUser" : "54c83f37e2e315bfbb43e98a" 
} 

我想与最新的更新日期一样的文件：

{ 
    "_id" : ObjectId("550286416fee741b0379c2d8"), 
    "lastUpdate" : ISODate("2015-03-12T16:00:00.000Z"), 
    "file" : "file1.pkg", 
    "idBook" : "54f6d1d8c239491400aa495e", 
    "idUser" : "54c83f37e2e315bfbb43e98a" 
}, 
{ 
    "_id" : ObjectId("560286416fee741b0379c24d"), 
    "lastUpdate" : ISODate("2015-03-12T16:00:00.000Z"), 
    "file" : "file2.pkg", 
    "idBook" : "54f6d1d8c239491400aa495e", 
    "idUser" : "54c83f37e2e315bfbb43e98a" 
} 

我怎样才能在猫鼬查询得到这样的结果？我是Mongoose和MongoDB的新手。

Answer 1

您可以使用aggregation pipeline做到这一点：

MyModel.aggregate([ 
    // Sort the docs by lastUpdate descending to put the newest ones first. 
    {$sort: {lastUpdate: -1}}, 
    // Group on file, taking the first (newest) doc for each file name. 
    {$group: { 
     _id: '$file', 
     doc: {$first: '$$ROOT'} 
    }} 
], function(err, docs) { 
    // Reshape the docs array into just the docs. 
    docs = docs.map(function(doc) { 
     return doc.doc; 
    }); 
    // docs contains your desired result 
})