find a specific ObjectId in array of embedded docs with ref in it

Question

This is my schema

var Schema = new Schema{
     name:String
     topics:[{item:{type: ObjectId, ref: 'tag'},comment:String}]
}

So 'topics' field contains an array of embedded docs. Each of those contains a ref and a string 'comment'. There is a way I can find a specific ref id (the item field)?

I tried some projection but this make some sense don't you think? Obiouvsly doesn't work..:)

    Model
    .find(
        { topics: {
            $in: [{     item: ObjectId("56e0aa684e7c55c414a51d82")      }]
        }
        },{name:1})
    .exec(function(err, data) {
        res.json(data)
    });

EDIT: I came up with this solution:

           Model
            .find(
                {'topics':
                    {$elemMatch :
                        {
                            item: "56e0aa684e7c55c414a51d82"
                        }
                    }
                }
            )
    .exec(function(err, data) {
        res.json(data)
    });

zangw · Accepted Answer · 2016-03-16 08:23:54Z

1

Please try this one

Model.find({'topics.item': "56e916772acfbbf805612555"}, {name: 1})
    .exec(function(err, data){
        if (err)
            console.log(err);
        else
            console.log(data);
    });

Test with data

{ "_id" : ObjectId("56e916772acfbbf805612559"), 
  "name" : "topic1", 
  "topics" : [
          { "item" : ObjectId("56e916772acfbbf805612555"), 
            "comment" : "tag1", 
            "_id" : ObjectId("56e916772acfbbf80561255b") }, 
          { "item" : ObjectId("56e916772acfbbf805612556"), 
            "comment" : "tag2", 
            "_id" : ObjectId("56e916772acfbbf80561255c") } ]
}

Return

[ { name: 'topic1', _id: 56e916772acfbbf805612559 } ]

answered Mar 16, 2016 at 8:23

zangw

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3 Comments

alfredopacino Over a year ago

thanks! please refer to my edit too, what's do you think is the better? The strange part of my solution is if I cast to ObjectId: item: mongoose.Schema.Types.ObjectId("56e0aa684e7c55c414a51d82") I get wrong results!

zangw Over a year ago

@the.websurfer, per this doc, Since the $elemMatch only specifies a single condition, the $elemMatch expression is not necessary, and instead you can use the following query: db.survey.find( { "results.product": "xyz" } )

zangw Over a year ago

@the.websurfer, you do not need to cast to ObjectId...in your wrong case.

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