How to remove a field from an array using aggregate on MongoDB?

Question

    {Crs:{[
       {Cr: {
            "_id" : ObjectId("5a75baada0f20bd4e612d480"),
            "Number" : 400,
            "Page" : 24,
            "DC" : "NE",
        }},
       {Cr: {
            "_id" : ObjectId("5a75baada0f20bd4e612d489"),
            "Number" : 300,
            "Page" : 14,
            "DC" : "100",
        }},
 ]}}

I have this data that i model using aggregate and I would like to know how can i remove "DC" field from all elements of the array using aggregate.

  >db.crs.aggregate(
    [
        {$group : {_id : null, crs : {$push : {cr : "$$ROOT"}}}},
        {$project : {_id : 0}}
    ]
)

This is what did to model that data. I think its something related with $project.

@chridam I'm really new in this so i didnt use any validate method. I just modeled the data that I imported from a csv file using aggregate. — pp fernandes
– pp fernandes, Commented Feb 5, 2018 at 13:46
Can you edit your question to show the actual JSON output that you get when you run the query db.crs.find({}).limit(2).pretty()? — chridam
– chridam, Commented Feb 5, 2018 at 14:47
@chridam Its kinda hard to do that because is this not my actual work, its just an example to understand better how this works. — pp fernandes
– pp fernandes, Commented Feb 5, 2018 at 14:56

Prashant Pokhriyal · Accepted Answer · 2019-09-11 09:10:23Z

2

First of all, your document is not a valid JSON schema. You might reconsider the following schema for that particular document.

{
    Crs:[
        {
            "_id" : ObjectId("5a75baada0f20bd4e612d480"),
            "Number" : 400,
            "Page" : 24,
            "DC" : "NE"
        },
        {
            "_id" : ObjectId("5a75baada0f20bd4e612d489"),
            "Number" : 300,
            "Page" : 14,
            "DC" : "100"
        }
    ]
}

Having above schema, you can easily remove DC field using $unset aggregate operator.

db.crs.aggregate([{$unset: 'Crs.DC'}]);

answered Sep 11, 2019 at 9:10

Prashant Pokhriyal

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