CODEWITHSUNDEEP
arraysmongodbslice
Matt Lightbourn
Matt Lightbourn

Reputation: 597

Mongo aggregate $slice to object instead of array

I have upgraded Mongo to 3.2 and am delighted that aggregating using $slice works. However, my problem is that I want to assign the value to an object not an array. I cannot find how to do this.

My script applied:

db.std_sourceBusinessData.aggregate(
  { $match : {objectType: "Account Balances"}},
  { $project: {_id: 1,entity_id: 1,accountBalances: 1}},
  { $unwind: "$accountBalances" },
  { $match: {"accountBalances": "Sales"}},
  {$project: {
      _id :1, 
      "Value" : {$slice: ["$accountBalances",1,1]},
      "key" : {$literal: "sales"},
      "company": "$entity_id"
  }}
)

Comes back with:

{
"_id" : ObjectId("566f3da3d58419e8b0fc76c7"),
"Value" : [ 
    "5428.64"
],
"key" : "sales"
}

Notice that Value is an array. What I want is:

{
"_id" : ObjectId("566f3da3d58419e8b0fc76c7"),
"Value" : "5428.64",
"key" : "sales"
}

Thanks, Matt

Upvotes: 1

Views: 1585

Answers (1)

JohnnyHK
JohnnyHK

Reputation: 311865

You can use $arrayElemAt instead of $slice to directly get a single array element.

Modify your final $project stage to be:

{$project: {
    _id: 1, 
    "Value": {$arrayElemAt: ["$accountBalances", 1]}, 
    "key": {$literal: "sales"},
    "company": "$entity_id"
}}

Upvotes: 4

Related Questions