mongodb aggregate that inserts an array into an existing array of a document

Question

I have a document in mongodb, like this one:

{ "_id" : "a", "array" : [ { "aa" : "11", "bb" : "22" } ] }

I want to insert an array in the array above, so the result looks like:

{"_id":"a","array":[{"aa":"11","bb":"22","cc":[{mm:"11"},{mm:"22"}]}]}

I am writing a node.js program and using the mongojs module to connect to mongodb. I have tried using db.collection.aggregate({"$unwind":"$name"}), but I don't know how to solve this.

did you try using $push to add the array field ?db.collection.update( { _id: "a" }, { $push: { array: {[{mm:"11"},{mm:"22"}]}}}) — s7vr
– s7vr, Commented Dec 12, 2016 at 16:05
The Aggregation framework is mean for reading data, but you appear to want to write to the document. Can you clarify exactly what you are looking to do? Do you want to add cc to the array in the document in the database or only during a read? — Pete Garafano
– Pete Garafano, Commented Dec 12, 2016 at 16:26

Jesse Kawell · Accepted Answer · 2019-09-23 15:25:15Z

1

If you want to update document then used update with push as below

db.collectionName.update(
  {"_id":"a"},
  {
    "$push":{
      "array":{
      "cc":[
        {"mm":"11"},
        {"mm":"22"}
      ]
    }
  }
})

Or if you want to add new field in aggregation then use project with literal as below

db.collectionName.aggregate({
  "$project":{
    "array":{
      "$map":{
        "input":"$array",
        "as":"el",
        "in":{
          "aa":"$$el.aa",
          "bb":"$$el.bb",
          "cc":{
            "$literal":[
              {"mm":"11"},
              {"mm":"22"}
            ]
          }
        }
      }
    }
  }
}).pretty()

edited Sep 23, 2019 at 15:25

Jesse Kawell

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answered Dec 12, 2016 at 16:18

Neo-coder

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5 Comments

Pete Garafano Over a year ago

My only concern here is $project doesn't actually add to the document in the database, just to the document returned. It is essentially ephemeral.

Neo-coder Over a year ago

@PeteGarafano So for this I was created two different query if OP want to update document then update work if want only in aggregation then aggregation ;), because OP not mentioned here to update document or not ?

Pete Garafano Over a year ago

I agree, OP's needs are unclear, I have commented asking for clarification

Courage Over a year ago

@Yogesh As PeteGarafano comment, 'Aggregation' is mean for reading, howerver as my code showed, I want to write the document. but if I type your code, the mongo console show: { "_id" : "a", "array" : [ { "aa" : "11", "bb" : "22" }, { "cc" : [ { "mm" : "11" }, { "mm" : "22" } ] } ] } what I mean is {"_id":"a","array":[{"aa":"11","bb":"22","cc":[{mm:"11"},{mm:"22"}]}]} I want to insert a array in first item of the array in the document. thanks your answer~

Courage Over a year ago

@all thanks everyone, I already solve this question with db.course.update({_id:1},{"$addToSet":{"arr.0.content":"ok"}}) Again thank you Yogesh and PeteGarafano time to reply my question

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