Add support for fields in LiveQuery

[rogerhu]

Issue Description

Parse LiveQuery specifications are supposed to take a fields in the query. Parse server does not handle these fields, nor do the iOS and Android clients.

https://github.com/ParsePlatform/parse-server/wiki/Parse-LiveQuery-Protocol-Specification

{
  "op": "subscribe",
  "requestId": 1,
  "query": {
      "className": "Player",
      "where": {"name": "test"},
      "fields": ["name"] // Optional
  },
  "sessionToken": "" // Optional
}

https://github.com/ParsePlatform/ParseLiveQuery-iOS-OSX/blob/master/Sources/ParseLiveQuery/Internal/QueryEncoder.swift

parse-community/ParseLiveQuery-Android#18

Steps to reproduce

Create a Parse Query with fields:

@ParseClassName("Message")
public class Message extends ParseObject {
    public static final String USER_ID_KEY = "userId";
    public static final String BODY_KEY = "body";

    public String getUserId() {
        return getString(USER_ID_KEY);
    }

    public String getBody() {
        return getString(BODY_KEY);
    }

    public void setUserId(String userId) {
        put(USER_ID_KEY, userId);
    }

    public void setBody(String body) {
        put(BODY_KEY, body);
    }
}

ParseLiveQueryClient<Message> parseLiveQueryClient =
                    ParseLiveQueryClient.Factory.getClient(new URI(ChatApplication.wsURI));

ParseQuery<Message> parseQuery = ParseQuery.getQuery(Message.class);
parseQuery.selectKeys(["userId"]);

            SubscriptionHandling<Message> subscriptionHandling = parseLiveQueryClient.subscribe(parseQuery);
            subscriptionHandling.handleEvents(
   new SubscriptionHandling.HandleEventsCallback<Message>() {
                        @Override
                        public void onEvents(ParseQuery<Message> query,
                                SubscriptionHandling.Event event,
                                Message object)
                        {
          }
}

Expected Results

Expect only fields to come out.

Actual Outcome

All fields are returned.

Environment Setup

• Server

  • parse-server version (Be specific! Don't say 'latest'.) : 2.3.7
  • Operating System: MacOS
  • Hardware: [FILL THIS OUT]
  • Localhost or remote server? (AWS, Heroku, Azure, Digital Ocean, etc): localhost, Heroku

• Database

  • MongoDB version: 3.2.1

Logs/Trace

Include all relevant logs. You can turn on additional logging by configuring VERBOSE=1 in your environment.

[TimNZ]

@flovilmart

I just went looking through JS SDK for fields support on live query subscriptions.

Can we just add an additional 'options' or 'fields' arg to 'subscribe' function in LiveQueryClient.js, and upstream subscribe functions that call it?

[flovilmart]

It would require some serverside work, i’ll Be happy to review a Pull Request :) that would be easier than the CLP’s

[TimNZ]

Oh, the server isn't complete either?
I was using the Live Query protocol wiki as a guide and hadn't looked at the server code.

Ok, will add to my future dev list :)

[TimNZ]

As far as I can tell Parse Server is using subscriptionInfo.fields if specified to filter the response object, before pushing it to the client.

Do you know for a fact that the server needs dev for this?

lib/LiveQuery/Client.js

_pushEvent(type: string): Function {
    return function(subscriptionId: number, parseObjectJSON: any): void {
      const response: Message = {
        'op' : type,
        'clientId' : this.id
      };
      if (typeof subscriptionId !== 'undefined') {
        response['requestId'] = subscriptionId;
      }
      if (typeof parseObjectJSON !== 'undefined') {
        let fields;
        if (this.subscriptionInfos.has(subscriptionId)) {
          fields = this.subscriptionInfos.get(subscriptionId).fields;
        }
        response['object'] = this._toJSONWithFields(parseObjectJSON, fields);
      }
      Client.pushResponse(this.parseWebSocket, JSON.stringify(response));
    }
  }

[montymxb]

@TimNZ we could always use more devs ;)

[TimNZ]

Ok, still on my todo list :)

[TimNZ]

Submitted pull.
No changes to server required.

parse-community/Parse-SDK-JS#518