Mongo DB $$ROOT on 2.4

[gabrielstuff]

Hello,

I'm trying to implement a group by query using agregate.

Here is the query : 

db['cfs.medias.filerecord'].aggregate(
   [
      {
       $project:
         {
           year: { $year: "$uploadedAt" },
           month: { $month: "$uploadedAt" },
           day: { $dayOfMonth: "$uploadedAt" },
           hour: { $hour: "$uploadedAt" },
           minutes: { $minute: "$uploadedAt" },
           seconds: { $second: "$uploadedAt" },
           milliseconds: { $millisecond: "$uploadedAt" },
           dayOfYear: { $dayOfYear: "$uploadedAt" },
           dayOfWeek: { $dayOfWeek: "$uploadedAt" },
           week: { $week: "$uploadedAt" }
         }
     },
     { "$group" :
         { "_id" : {
                "year" : "$year",
                "month" : "$month",
                "day" : "$day"
             },
          "medias": {
                "$push":  {id:"$_id"}
                }
          }
      }
   ]
);

I'd like to push the current document inside the medias Array instead of its id. How would one do that with mongo 2.4 ?

Thanks a lot !

[Will Berkeley]

$$ROOT isn't available. As an approximation, you can use $addToSet or $push to add all the documents fields explicitly. For example,

> db.test.drop()
> db.test.insert({ "_id" : 0, "a" : 1, "b" : 2, "c" : 3 })
> db.test.insert({ "_id" : 1, "a" : 1, "b" : 4, "c" : 5 })
> db.test.aggregate([
    { "$group" : { "_id" : "$a", "bs" : { "$push" : "$b" }, "cs" : { "$push" : "$c" } } }
])
{ "_id" : 1, "bs" : [ 2, 4 ], "cs" : [ 3, 5 ] }

What are you trying to do with this pipeline, exactly? It's often a sort of anti-pattern to be trying to write a pipeline that wants to store all the documents of a group using $$ROOT, or, somewhat similarly, to want an output from a pipeline that looks like the documents from the original collection, though occasionally it's reasonable.

-Will