Mongodb : array element projection with findOneAndUpdate doesn't work?

Question

I am using Mongoose and I'm trying to update an array element and get it back updated. This is my document structure :

{   name:String,
    friends:[
        {   name:String,
            age:Number
        }
    ]
}

When I execute the following query I get all the friends in the result but I only want to get 25 year old friends back :

theCollection.findOneAndUpdate(
    {   name : 'cherif',
        'friends.name':'kevin'
    },
    {   $set:{
            'friends.$.age':25
        }
    },
    {   friends:
        {   $elemMatch:
            {   age : 25 } 
        }
    },
    function(err,result){
        if (!err) {
            console.log(result);
        }});

JohnnyHK · Accepted Answer · 2013-09-24 16:51:58Z

11

As the docs for findOneAndUpdate specify, you need to include your projection object as the select property of the options parameter:

theCollection.findOneAndUpdate(
    {   name : 'cherif',
        'friends.name':'kevin'
    },
    {   $set:{
            'friends.$.age':25
        }
    },
    {   select: { 
            friends: {
               $elemMatch: 
               {   age : 25 } 
            }
        }
    },
    function(err,result){
        if (!err) {
            console.log(result);
        }
    });

answered Sep 24, 2013 at 16:51

JohnnyHK

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4 Comments

KwiZ Over a year ago

Is it possible to use $ projection here? For example Doc.findOneAndUpdate({ _id: id, 'comments._id': cmtId }, {...}, { select: 'comments.$': 1 }). I've tried this but strangely it returned { comments: [{}, {}, {}], _id:... }

admrply Over a year ago

@KwiZ Did you ever find a solution for this? I'm trying to use $ projection in the same way but with no luck!

JohnnyHK Over a year ago

@admrply Go ahead and post a new question with the full details about what you're trying to do.

Rui Sebastião Over a year ago

the answer to @KwiZ is use 0 instead of $ ( { select: 'comments.0': 1 })

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