How to filter custom fields?

I’m trying to filter the fields with the custom directive, but I can’t find a way to implement it.

This is the graphql schema I defined

type Spot @remote {
    value: Int @search

type Device {
    id: ID!
    name: String! @id
    temperature: Spot! @custom(http: {
        url: "$name/spots/temperature",
        method: GET

After doing the mutation, I want to find out all the devices whose temperature value is higher than 0, so I made the following query

query {
    queryDevice {
        temperature (filter:{value:{gt:0}}) {

I found that I cannot do that because the remote type is not part of the dgraph and the custom field cannot be filtered.I have also read the lambda command and made various attempts, but I don’t know how to achieve this kind of filtering.

How should I implement that kind of query, or am I wrong in the first place?