MongoDB aggregation sort not working

问题:

I'm having a problem applying a sort to an aggregation grouping. My raw data looks like the following:

    {             "_id" : ObjectId("52deab2fe4b0a491abb54108"),             "type" : "build",             "time" : ISODate("2014-01-21T17:15:27.471Z"),             "data" : {                     "buildNumber" : 43,                     "buildDuration" : 997308,                     "buildProjectName" : "TestABC",                     "buildResult" : "SUCCESS"             }     } 

I would like to sort this first by buildProjectName and then date. Here is my query:

db.builds.aggregate([     { $group: {          _id: {              month: { $month: "$time" },             day: { $dayOfYear: "$time" },             year: { $year: "$time" },              buildProjectName: "$data.buildProjectName",          },         buildDuration: { $avg: "$data.buildDuration" }      } },     { $sort: {buildProjectName: 1, year: 1, month: 1, day: 1} } ]) 

I've tried switching the order of the sort (i.e.: buildProjectName, day, month, year), but I always get the same result with the dates out of order:

{         "result" : [                 {                         "_id" : {                                 "month" : 1,                                 "day" : 20,                                 "year" : 2014,                                 "buildProjectName" : "TestABC"                         },                         "buildDuration" : 1170723.5                 },                 {                         "_id" : {                                 "month" : 1,                                 "day" : 21,                                 "year" : 2014,                                 "buildProjectName" : "TestABC"                         },                         "buildDuration" : 2284863.3333333335                 },                 {                         "_id" : {                                 "month" : 1,                                 "day" : 17,                                 "year" : 2014,                                 "buildProjectName" : "TestABC"                         },                         "buildDuration" : 2234662                 }         ],         "ok" : 1 } 

回答1:

The fields you're sorting on are part of the _id so you need to include that in your $sort field names:

db.builds.aggregate([     { $group: {          _id: {              month: { $month: "$time" },             day: { $dayOfYear: "$time" },             year: { $year: "$time" },              buildProjectName: "$data.buildProjectName",          },         buildDuration: { $avg: "$data.buildDuration" }      } },     { $sort: {         '_id.buildProjectName': 1,          '_id.year': 1,          '_id.month': 1,          '_id.day': 1     } } ]) 

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