Select users not in array of pointers - arrays

Question

Using Parse.com and its Cloud code, I want to fetch users that are not in array of users.
...
var query = new Parse.Query(Parse.User);
query.notContainedIn("objectId", request.object.get("recipients"));
...
query.find().then(
function(results) {
console.log("# of users:" + results.length);
},
function(error) {
console.error(error)
}
);
The constraint notContainedIn doesn't seem to work, all users are returned, not just the ones not contained in the recipients array coming as part of the request object.
The recipients array in REST request is defined like this
"recipients":[
{"__type":"Pointer","className":"_User","objectId":"qwerty1234"},
{"__type":"Pointer","className":"_User","objectId":"asdfgh1234"}]
The data I get as part of the request is ok, because e.g. request.object.get("recipients")[0].id returns the qwerty1234 value.
What am I doing wrong here?

Answer 1

You are asking parse to compare the objectId to an array of pointers. This would work fine if the column was a Pointer to a User, but you're using just the ID.
The easy solution is to map or extract the ID from the array of pointers, e.g.
// at the top, so you can use the Underscore library
var _ = require('underscore');
// ...
// in your Cloud function
var query = new Parse.Query(Parse.User);
// _.pluck() creates an array of a property from each object in the parent array
var recipientObjectIds = _.pluck(request.object.get('recipients'), 'objectId');
query.notContainedIn('objectId', recipientObjectIds);