How to select specific sub-documents by criteria?

Question

MongoDB

Having such a scheme of articles with subdocuments of comments, you need to select only certain authors

article: {
        text: {type: String, require: true},
        comments: [{
            text: {type: String, required: true},
            user_id: {
                type: mongoose.Schema.Types.ObjectId,
                ref: 'users'
            }
        }],
        created_at: { type: Date,  "default": Date.now}
    },

Wrote this query

db.getCollection('article').findOne({
        '_id': ObjectId("564680c59bfd4a0a49745282"),
        'comments.user_id': {$in : [ObjectId("563e3337e2bf6c431b297d41"), ObjectId("563e3337e2bf6c431b297d42")]}
        })

I expected to see comments only from these authors, but I see from everyone. Apparently, according to 1 condition with Id, mongo pulls out all the data for this article, I went further, wrote such a request

db.getCollection('article').find(
        {'_id': ObjectId("564680c59bfd4a0a49745282")},
        { comments : { $elemMatch: { user_id : {$in : [ObjectId("563e3337e2bf6c431b297d41"),ObjectId("563e3337e2bf6c431b297d42") ]}} } } 
        )

but also everything is not correct, it returns only 1 record,
please tell me how to solve this seemingly simple task.

Answer 1

if I don't confuse anything, in the second request you need to specify "storage" ('comments') as a key, and not what we are looking for, but in $elemMatch we are already talking about what, only just 'user_id'

Answer 2

The find command is designed to find the documents themselves, not their contents (although there are partial get functions). Therefore, you can receive documents completely and filter them already on the "client", if you filter a lot, then it makes sense to select comments in a separate collection.