Question

Let’s say I have two types of MongoDB documents: ‘Projects’ and ‘Tasks’. A Project can have many tasks. In my case it is more suitable to link the documents rather than embed.

When a user wants to save a task I first verify that the project the task is being assigned to exists, like so:

// Create new task
var task = new Task(data);
// Make sure project exists
Project.findById(task.project, function(err, project) {
  if(project) {
    // If project exists, save task
    task.save(function(err){
      ...    
    });
  } else {
    // Project not found
  }
});

My concern is that if another user happens to delete the project after the Project.findById() query is run, but before the task is saved, the task will be created anyway without a referenced project.

Is this a valid concern? Is there any practice that would prevent this from happening, or is this just something that has to be faced with MongoDB?

Answer 1

Technically yes, this is something you need to face when using MongoDB. But it’s not really a big deal as it’s rarely someone to delete a project and another person is unaware of it and creating task for that project. I would not use the if statement to check the project status, rather just leave task created as a bad record. You can either manually remove those bad records or schedule a cron task to clean them.