CODEWITHSUNDEEP
node.jsmongodbmongodb-query
tsturzl
tsturzl

Reputation: 3137

MongoDB cannot project string value from _id

I have an aggregate to pull metrics from a collection of "share" actions. These metrics are grouped by day and the platform(twitter, pintrest, etc). Each stage works fine except when it comes to formatting the output in a $project stage, I cannot seem to get the platform string to project in my output. I see it in the _id still, however I cannot get it to project to the other field.

The aggregation is as follows:

{
  $unwind: "$platforms"
},
{
  $project: {
    day: {$dayOfMonth: "$created_at"},
    month: {$month: "$created_at"},
    year: {$year: "$created_at"},
    platforms: 1
  }
},
{
  $group: {
    _id: {
      platorms: "$platforms",
      day: "$day",
      month: "$month",
      year: "$year"
    },
    count: {$sum: 1}
  }
},
{
  $project: {
    day: "$_id.day",
    month: "$_id.month",
    year: "$_id.year",
    platform: "$_id.platforms",
    count: 1
  }
}

The output of the following is:

{
"result" : [ 
    {
        "_id" : {
            "platorms" : "EMAIL",
            "day" : 28,
            "month" : 4,
            "year" : 2015
        },
        "count" : 1,
        "day" : 28,
        "month" : 4,
        "year" : 2015
    }, 
    {
        "_id" : {
            "platorms" : "EMAIL",
            "day" : 27,
            "month" : 4,
            "year" : 2015
        },
        "count" : 10,
        "day" : 27,
        "month" : 4,
        "year" : 2015
    }, 
    {
        "_id" : {
            "platorms" : "SMS",
            "day" : 27,
            "month" : 4,
            "year" : 2015
        },
        "count" : 1,
        "day" : 27,
        "month" : 4,
        "year" : 2015
    }, 
    {
        "_id" : {
            "platorms" : "FACEBOOK",
            "day" : 27,
            "month" : 4,
            "year" : 2015
        },
        "count" : 1,
        "day" : 27,
        "month" : 4,
        "year" : 2015
    }, ...

The integers for day, month, and year project fine, however platforms does not.

Upvotes: 0

Views: 137

Answers (1)

Sede
Sede

Reputation: 61293

This is because in your $group stage you have compound _id with platorms: "$platforms" (missing f in field name) and you are projecting the $_id.platforms in your last $project stage and since such field doesn't exist you will not get any result. You can also exclude the _id field using _id: 0.

Change your $group stage to:

{
  $group: {
    _id: {
      platforms: "$platforms",
      day: "$day",
      month: "$month",
      year: "$year"
    },
    count: {$sum: 1}
  }
}

Upvotes: 1

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