MongoDB replace value during aggregation

Question

Suppose this document:

{
    _id : Object(“12918”),
    username : “username”,
    password : “password”,
    occupation: {
        name : “Football”,
        code : 254,
    }
},
{
    _id : Object(“12919”),
    username : “username2”,
    password : “password2”,
    occupation: {
        name : “Basketball”,
        code : 255,
    }
}

I want a query that returns:

{
    _id : Object(“12918”),
    occupation : {
        name : “*”,
        code : 254
    }
},
{
    _id : Object(“12919”),
    occupation : {
        name : “*”,
        code : 255
    }
}

So, a query that just returns the fields _id and occupation. And the field occupation.name must be replaced by * in all records.

I tried this query:

aggregate([
    {
        "$project" : 
        { 
            "_id" : 1, 
            “occupation" : 1,
            “occupation.name" : { $literal:“*” } 
        } 
    }
])

which returned the following exception:

{ "ok" : 0, "errmsg" : "can't add an expression for field occupation because there is already an expression for that field or one of its sub-fields.", "code" : 16400 }

Is there a way to achieve this?

What is your mongo server version ?

s7vr
– s7vr

2017-02-22 18:21:53 +00:00
Commented Feb 22, 2017 at 18:21 — s7vr
– s7vr, Commented Feb 22, 2017 at 18:21
It's version 3.0.1

José Miguel Melo
– José Miguel Melo

2017-02-22 18:25:40 +00:00
Commented Feb 22, 2017 at 18:25 — José Miguel Melo
– José Miguel Melo, Commented Feb 22, 2017 at 18:25

Bertrand Martel · Accepted Answer · 2017-02-22 18:26:00Z

3

You can specify the nested document projection of occupation like this :

db.test.aggregate([{
    "$project": {
        "_id": 1,
        "occupation": {
            code: 1,
            name: { $literal: "*" }
        }
    }
}])

answered Feb 22, 2017 at 18:26

Bertrand Martel

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2 Comments

José Miguel Melo Over a year ago

Thank you Bertrand!

Mir Hussain Over a year ago

but how too using 0 or 1 value replace with other value because when using 0 or 1 value using for hide and show key but how to using 0 or 1 value for replace previous value

Hasan Alper Ocalan · Accepted Answer · 2017-02-22 18:26:30Z

2

You can do it like this :

db.collectionName.aggregate([{$project:{
           _id:1,
           occupation:{"name":{$literal:"*"},
                       "code":"$occupation.code"
                      } 
           }    
   }])

answered Feb 22, 2017 at 18:26

Hasan Alper Ocalan

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