Find objects not in a relation - parse-platform

Question

I have a custom object Team in Parse with a relation field for the default User object. What I would like to do is retrieve all User objects which are not related to any Team object. Can anyone point me in the right direction on how to do this using the JavaScript SDK? I've been going over the documentation for the Query object but I can't find anything.
Perhaps another type of relation, or placing the relation at another place is a better solution. What I want to accomplish is the following: Each user is allowed to be in one team and one team only. In addition I need to be able to query the following information from Parse:
I want to retrieve the User objects of all the users assigned to a team
I want to retrieve the User objects of all the users who are not assigned to any team
I have tried using a join table with both the user and team object ids. Then I tried to following query to get all users not assigned to a team:
var teammember = Parse.Object.extend('TeamMember'),
query = new Parse.Query("User");
var innerQuery = new Parse.Query("TeamMember");
query.doesNotMatchQuery('user', innerQuery);
query.find({
success: function(results) {
response.success(results);
},
error : function(error) {
response.error(error);
}
})
But this just gets me the following response: error: "{"code":102,"message":"bad type for $notInQuery"}".
I like the Relation type as I can add or remove multiple members at once with a single call to the REST API. I also have no problems retrieving the information on team members when using the Relation type to connect the users to the teams. It is just getting the users which are not assigned to any team that is giving me problems.

Answer 1

It doesn't sound like you need a relation at all. Instead, add a Pointer column to User that points to Team. It ensures that a User can only belong to one team, and your other requirements can be captured as follows.
// All users assigned to a team
query = new Parse.Query('User');
query.exists('team');
// All users assigned to a specific team
query = new Parse.Query('User');
query.equalTo('team', specificTeam);
// All unassigned users
query = new Parse.Query('User');
query.doesNotExist('team');
Update: If you need to support multiple teams per User in the future, then I would suggest creating a Parse table called Membership with two columns: a Pointer to User and a Pointer to Team. This essentially gives you more control than relying on Parse relations, but it gets a little more complicated.
_ = require('underscore'); // Or lodash
// All users assigned to a team
query = new Parse.Query('Membership');
query.find().then(function (results) {
// http://underscorejs.org/#uniq
users = _.uniq(results, false, function (user) { return user.id; });
});
// All users assigned to a specific team
query = new Parse.Query('Membership');
query.equalTo('team', specificTeam);
// All unassigned users
var assignedUsers = []
var unassignedUsers = []
memberQuery = new Parse.Query('Membership');
userQuery = new Parse.Query('User');
memberQuery.find().then(function (memberResults) {
// http://underscorejs.org/#map
var ids = _.map(memberResults, function (user) { return user.id; });
// http://underscore.js.org/#uniq
assignedUsers = _.uniq(ids);
userQuery.find();
}).then(function (userResults) {
var users = _.map(userResults, function (user) { return user.id; });
// http://underscorejs.org/#difference
unassignedUsers = _.difference(users, assignedUsers);
});
To add and remove Users to/from Teams, you would create Membership objects and save API calls with Parse.Object.saveAll() and Parse.Object.destroyAll().

Answer 2

I ran into trouble with the answer provided by Seth. When retrieving the users not assigned to a team the difference between the two arrays would be incorrect. I am assuming this is due to the assignedUsers having object of type Membership and userResults being of type User. This would make it impossible for underscore to make a proper match.
I would up using this as my Cloud Code:
Parse.Cloud.define("getTeamlessUsers", function(request, response) {
var _ = require("underscore"),
assignedUsers = [],
companyUsers = [],
memberQuery = new Parse.Query("TeamMembers"),
userQuery = new Parse.Query("User"),
index,
ubound;
memberQuery.find().then(function(memberResults) {
// Make sure each User ID will appear just once
memberResults = _.unique(memberResults, false, function(item) { return item.get('user').id; });
// Loop over the unique team members and push the User ID into the array
for (index = 0, ubound = memberResults.length; index < ubound; index++) {
var user = memberResults[index].get("user");
assignedUsers.push(user.id);
}
// Get al the users
return userQuery.find();
}).then(function(userResults) {
// Loop over all the users and push the ID into the array
for (index = 0, ubound = userResults.length; index < ubound; index++) {
companyUsers.push(userResults[index].id);
}
// Create an array of user IDs which are not present in the assignedUsers array
var result = _.difference(companyUsers, assignedUsers);
// Return the IDs of user not assigned to any team
response.success(result);
}).fail(function(error) {
response.error(error);
});
});