Mongodb：在嵌套数组属性中查找ids $

Question

I have the following data structure for my users in my mongodb:

{
    _id: "someId",
    profile: {
        username: "oliv",
        friendRequests: [
            { fromUserId: "anId", accepted: false, created: "someDate"},
            { fromUserId: "otherId", accepted: true, created: "otherDate"}
        ]
}

I'd like to retrieve the user objects that are referenced in my logged user's friendsRequested . So I tried something like this:

Meteor.users.find({_id: {$in: Meteor.user().profile.friendRequests.fromUserId}});
// FYI: Meteor.users is the collection and Meteor.user() retrieves the current user

But it's not working. I'm assuming it's because of the nested array.
Is there any way of telling mongo to iterate through the fromUserId or something?

Thanks

Answer 1

Change your query to:

Meteor.users.find({_id: {$in: _.pluck(Meteor.user().profile.friendRequests, 'fromUserId') }});

Reasoning:

friendRequests is an array of objects, and $in wants an array of strings(the ids), using _.pluck you're able to pass an array of objects, and tell _ to only return the field fromUserId for each object in the array.

Question in comment ("what if I only want to get the ids from friend requests where "accepted" is false?"):

_.pluck(
    _.filter(Meteor.user().profile.friendRequests, function (req) {
        return !req.accepted;
    }),
    'fromUserid'
);

Underscore filter docs