Mongoose Query resolves even if it wasn't awaited

[samislam]

I have the following Model:

const userSchema = new mongoose.Schema({
  // long long schema... etc
  age: Number,
})
const UserModel = mongoose.model('User', userSchema, 'users')

I have the following function:

async function x(y) {
  // @param y: function | asyncfunction
  const YreturnValue = await y()
  YreturnValue.sort('age')
  return YreturnValue // returns a Mongoose Query
}

and I have the following route:

router.route('/').get(async (req, res, next) => {
  const query = await x(() => UserModel.find({}))
  const docs = await query 
  res.status(200).json({ data: docs })
})

When I request the GET /, I get this error:

I am awaiting the function x because it's an async function (i.e, it returns a Promise), and the resolved value of the function x is expected to be a mongoose Query object.

• the function x receives one argument, a function, or an async function, in both cases, your argument must return a mongoose Query object.

What's the problem?

I have asked this question on StackOverflow, but I didn't get any fulfilling response.
https://stackoverflow.com/posts/73166696/edit

[josegl]

I think that the problem comes because you are awaiting the y function inside the x function. That will return the query results, but I guess that what you want actually is to sort the query, and for such case you should act like this:

// @param y: function | asyncfunction
function x(y) {
  return new Promise((resolve, reject) => {
    y.sort('age').exec((err, results) => {
      if(err){
        reject(err);
      }else{
        resolve(results);
      }
    });
  });  
}

In your version:

async function x(y) {
  // @param y: function | asyncfunction
  const YreturnValue = await y()
  YreturnValue.sort('age')
  return YreturnValue // returns a Mongoose Query
}

When you await the y function it resolves to the query results, so YreturnValue is not a Query as you think, it is an array, and when you want to sort, what you are sorting is an array, so it fails because the sort function expects a function or undefined.

You maybe could try this version that I'm not sure if it would work:

// @param y: function | asyncfunction
async function x(y) {
  sortedQuery = y.sort('age');
  const YreturnValue = await sortedQuery();
  return YreturnValue // returns an Array
}

If what you want is to return a Query instance with the sort configuration, then you could try:

// @param y: function | asyncfunction
async function x(y) {
  sortedQuery = y.sort('age');
  return sortedQuery;
}

And then here:

router.route('/').get(async (req, res, next) => {
  const query = await x(() => UserModel.find({}))
  const docs = await query 
  res.status(200).json({ data: docs })
})

query will be an actual Mongoose Query with the sort configuration applied. However as I said above, I'm not sure if you can await a sorted query and get the results, or if you have to use the first implementation that I suggested.

[vkarpov15]

If you return something that has a then() function from an async function, JavaScript will automatically call then(). There's no way to return a thenable from an async function.

You would have to wrap your query in an object, like:

async function x(y) {
  // @param y: function | asyncfunction
  const YreturnValue = await y()
  YreturnValue.sort('age')
  return { query: YreturnValue } // returns a Mongoose Query
}