How can I pass additional query parameters in a REST put operation?

[CosmoMyzrailGorynych]

I would like to update an item inside a document's array via positional operator $ of Mongoose/MongoDB query, and thus need to not only pass ID of an updated document but also an additional query for array objects. Despite all attempts Mongoose says that "The positional operator did not find the match needed from the query. Unexpanded update: faculcies.$.name".

I call 'PUT' on URL like /univercities/{docID}?faculcies._id={faculcyID} via fetch:

fetch(`/univercities/${this.parent.univercity._id}?faculcies._id=${this.faculcy._id}`, {
    method: 'put',
    body:  JSON.stringify({
        '$set': {
            'faculcies.$.name': this.faculcy.name
        }
    }),
    headers: {
        Accept: 'application/json',
        'Content-Type': 'application/json',
        Authorization: sessionStorage.accessToken
    }
})
.then( … )

The hook.params.query becomes { 'faculcies._id': '589d3fc48fe3632ed854beee' }, but this additional query seems to be ignored. All IDs are valid and there are no spelling mistakes.
It is also impossible to 'PUT' something on /univercities?_id={univercityID}&faculcies._id={faculcyID}.

Am I missing something? Or is it something just not implemented?

[marshallswain]

@CosmoMyzrailGorynych I haven't tried that, yet. Can you set a breakpoint in feathers-mongoose and verify that the data is getting passed in properly?

[daffl]

From what I understand, faculcies is an array but faculcies._id will try to query for { faculcies: { _id } }. You will have to use the $elemMatch selector to find items in an array.

[DominikTrenz]

I can't get it working neither. I tried this:
userService.update({ "_id":"mainDocumentID", "subdocs": {$elemMatch: {_id: "someId"}} }, { $set:{ "subdocs.$.last_name":"New Lastname" } })
and that:
userService.update({ "_id":"mainDocumentID", "subdocs._id":"someId" }, { $set:{ "subdocs.$.last_name":"New Lastname" } })
as supposed in this threads:
https://stackoverflow.com/questions/20262405/update-array-element-by-id-with-mongo-query
https://stackoverflow.com/questions/37612448/mongodb-positional-operator-error

What am i missing?