Finding nested array data with elemMatch in MongoDB/Meteor

Question

collection structure as such:

{"_id" : "abc",
"potentialUsers" : [{"userID" : "def"}, 
                    {"userID" : "ghi"}]
},

{"_id" : "123",
"potentialUsers" : [{"userID" : "456"}, 
                    {"userID" : "789"}]
},

I want to query if user abc has the user def in their potential users array. My current query (client) is

    getPendingLiftRequests: function() {
        return collection.find({}, {potentialUsers: {$elemMatch: {userID: Meteor.user().services.facebook.id}}});
    }

On the server I publish all of that collection to the user, and then just selectively show it based on the view of the client. However, when I try to use an elemMatch on the array, it just shows all of the records, when it should only show 1.

I don't know meteor, but that {} as first argument in a mongo find looks pretty suspicious. It looks like an empty query which returns all documents. What is the first argument supposed to be? — Mario Trucco
– Mario Trucco, Commented Sep 7, 2015 at 21:51

David Weldon · Accepted Answer · 2015-09-07 21:58:46Z

2

You don't need $elemMatch here. This should work:

var fId = Meteor.user().services.facebook.id;
return collection.find({'potentialUsers.userID': fid});

answered Sep 7, 2015 at 21:58

David Weldon

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Stuiterbal · Accepted Answer · 2015-11-09 15:10:43Z

2

Have look at the documentation for minimongo in Meteor: http://docs.meteor.com/#/full/find

You have to use the fields option to get the desired result.

getPendingLiftRequests: function() {
    return collection.find({}, { fields: { potentialUsers: {$elemMatch: {userID: Meteor.user().services.facebook.id}}}});
}

answered Nov 9, 2015 at 15:10

Stuiterbal

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