Promises w/ Parse Cloud Code Example

gistfile1.txt

Parse.Cloud.beforeSave("Entry", function(request, response) {
    var entry = request.object;
    var contest = request.object.get("contest");

    var fetchedUser, fetchedContest;
    var errorMessage;

    entry.get("user").fetch().then(function(result) {
        fetchedUser = result;
        return contest.fetch();
    }).then(function(result) {
        fetchedContest = result;
        return fetchedContest.get("timeSlot").fetch();
    }).then(function(fetchedTimeSlot) {
        // now we have all the variables we need to determine validity
        var now = new Date();
        var hasSufficientFunds = fetchedUser.get("fundsAvailable") >= fetchedContest.get("entryFee");
        var contestNotStarted = fetchedTimeSlot.get("startDate") >= now;
        if (hasSufficientFunds && contestNotStarted) {
            contest.increment("entriesCount");
            contest.increment("entriesLimit", 0); //have to do this, otherwise entriesLimit is undefined in save callback (?)
            return contest.save();
        } else {
            errorMessage = (hasSufficientFunds)? 'This contest has already started.' : 'Insufficient Funds.';
            return null;
        }
    }).then(function(result) {
        if (!result) {
            response.error(errorMessage);
        } else {
            if (contest.get("entriesCount") > contest.get("entriesLimit")) {
                response.error('The contest is full.');
            } else {
                response.success();
            }
        }
    }, function(error) {
        response.error(error);
    });
});