CODEWITHSUNDEEP
mongodbaggregation-framework
Bongsakorn
Bongsakorn

Reputation: 27

Mongo projection field that field not same

there

My question may be confuse. Let's me explain further more.

I have document for aggregation like this.

{
  "metric" : "user_act",
  "stream_id" : "f00001",
  "values" : {
    "likes" : 57,
    "comments" : 0,
    "shares" : 0
  }
}
{
    "metric" : "user_act",
    "stream_id" : "f00002",
    "values" : {
      "likes" : 28,
      "comments" : 0,
      "shares" : 1
    }
}

{
    "metric" : "user_act",
    "stream_id" : "t00001",
    "values" : {
      "favorites" : 5,
      "retweets" : 15
    }
}

I would like to calculate engagement by sum likes, comments and shares together. So before calculating, I have to projection data before grouping. I would like to mapping values.favorites to likes, values.retweets to shares and comments if don't have any data set default to 0.

I try projection like below but does not work because value of second line of $ifNull override the first line.

{
  $project: {
    "stream_id" : 1, 
    "shares": {
      $ifNull: ["$values.retweets",0],
      $ifNull: ["$values.shares", 0]
    } ,
    "likes": {
      $ifNull: ["$values.favorites",0],
      $ifNull: ["$values.likes", 0]
    } ,
    "comments": {
      $ifNull: ["$values.replys",0],
      $ifNull: ["$values.comments", 0]
    }
  }
}

Anyone any idea? Thank you in advanced.

[Update] I try to projection like this but not work in case: how can I check the field exists?

{
  $project: {
    "stream_id" : 1,
      "shares": {
        $switch: {
          branches: [
            { case: {$ne: ["$values.retweets", 0]},
              then: {$ifNull: ["$values.retweets", "$values.retweets"]}
            },
            { case: {$ne: ["$values.shares", 0]},
              then: {$ifNull: ["$values.shares", "$values.shares"]}
            }
          ],
          default: 0
        }
      }
  }
}

Upvotes: 2

Views: 166

Answers (1)

s7vr
s7vr

Reputation: 75994

You can try $cond projection.

db.collection.aggregate({
  $project: {
    "stream_id" : 1, 
    "shares": { $cond: [ { $eq:[ { $ifNull: [ "$values.shares", 0 ] }, 0 ] },{ $ifNull: [ "$values.retweets", 0 ] }, "$values.shares" ] },
    "likes": { $cond: [ { $eq:[ { $ifNull: [ "$values.likes", 0 ] }, 0 ] }, { $ifNull: [ "$values.favorites", 0 ] }, "$values.likes" ] },
    "comments": { $cond: [ { $eq:[ { $ifNull: [ "$values.comments", 0] }, 0 ] }, { $ifNull: [ "$values.replys", 0 ] }, "$values.comments" ] }
}})

Using $switch

db.collection.aggregate([{
  $project: {
    "stream_id" : 1,
      "shares": {
        $switch: {
          branches: [
            { case: { $ifNull: [ "$values.shares", false ] },
              then: "$values.shares"
            },
           { case: { $ifNull: [ "$values.retweets", false ] },
              then: "$values.retweets"
            }],
          default: 0
        }
      }
  }
}])

Upvotes: 1

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