How to select only unique values ​​from MongoDB?

Question

NoSQL

Good afternoon!
Let's say we have a collection like this:

[{
  "task":       1,
  "creator":    1,
  "progress" :  0,
}, {
  "task":       1,
  "creator":    1,
  "progress" :  0.3,
}, {
  "task":       1,
  "creator":    1,
  "progress" :  0.7,
}, {
  "task":       2,
  "creator":    1,
  "progress" :  0.1,
}, {
  "task":       2,
  "creator":    1,
  "progress" :  0.5,
}, {
  "task":       2,
  "creator":    1,
  "progress" :  0.9,
}]

those. we have a user ID, a task ID and its progress.
The task is as follows: select only the latest (unique) progress for each task, for a specific user.
Those. the output should be:

[{
  "task":       1,
  "creator":    1,
  "progress" :  0.7,
}, {
  "task":       2,
  "creator":    1,
  "progress" :  0.9,
}]

Now I tried to do

const uniqTasks = Task.find({
  creator:  1
})
  .distinct('task')
  .exec();

This gives us a dictionary, and then findOne + sort({_id: -1}) in Promise.all.

Promise.all(uniqTasks.map(task) => {
  return Task.findOne({
    creator:  1,
    task: task
  })
    .sort({_id: -1})
    .exec();
});

As you understand, these are N parallel queries to the database, that is, to put it mildly, shit code. How can these queries be aggregated so that the output has the same result?

Answer 1

Do not store duplicates and that's all.