Simultaneous beforeSave actions permitting repetitions

To prevent certain objects from being created, I incorporated a conditional in the beforeSave cloud function of that object type.

However, when two objects are created at the same time, the conditional fails to work as expected.

Check out my code snippet below:

Parse.Cloud.beforeSave("Entry", function(request, response) {
    var theContest = request.object.get("contest");
    theContest.fetch().then(function(contest){
      if (contest.get("isFilled") == true) {
          response.error('This contest is full.');
      } else {
          response.success();
    });
});

The goal is to prevent an Entry object creation if a Contest is already at maximum capacity. However, in situations where there is only 1 spot left in the Contest and two entries are saved simultaneously, both end up getting added.

I understand this scenario may be rare, but it's still a valid concern.

javascriptparse-platformparse-cloud-code

Answer №1

Utilizing Mongodb, Parse leverages a NoSQL database known for its scalability but lacking in synchronization capabilities. The key element required here is mutual exclusion, an aspect not directly supported on a Boolean field. However, Parse offers atomicity for counters and array fields to help impose some level of control.

For more information, check out these resources: and

Answer №2

Resolved the issue by implementing an increment method and performing the check in the save callback function rather than retrieving the object and checking a Boolean value.

Here is a snippet of the solution:

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

  theContest.increment("entries");
  theContest.save().then(function(contest) {
    if (contest.get("entries") > contest.get("maxEntries")) {
      response.error('The contest is full.');
    } else {
      response.success();
    }
  });
}

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