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Question

Im new to promises and I'm trying to to return the value of a promise like mongoose does but using mongoskin and bluebird. This works with mongoose return User.find().then(users => users) . This will return a list of users not a promise in apollo-server resolvers.

I've tried promise generator and async but with no luck. From what I've read a promise always returns a promise so no idea how mongoose is returning a value.

mongodb.js

import Promise from 'bluebird';
import mongoskin from 'mongoskin';

Object.keys(mongoskin).forEach(function (key) {
  var value = mongoskin[key];
  if (typeof value === 'function') {
    Promise.promisifyAll(value);
    Promise.promisifyAll(value.prototype);
  }
});

Promise.promisifyAll(mongoskin);

export default {
  connect (uri) {
    return mongoskin.db(uri, {native_parser:true});
  }
};

users.js

import mongodb from '../../databases/mongodb';

export default class User {
  constructor () {
    this.db = mongodb.connect('mongodb://127.0.0.1:27017/test', {native_parser:true});
    this.collection = this.db.collection('users');
  }

  find (query = {}, options = {}) {
    const findAsync = () => {
      return Promise.resolve().then(() => {
        return this.collection.findAsync(query, options);
     })
     .then((xx) => {
        xx.toArray((err, items) => {
         if (err) return err;
        return items;
       });
     });

    };

    async function getData () {
      let foo = await findAsync();

      return foo;
    }

    return getData();
  }
}

const user = new User();

function bar () {
  return user.find().then(x => console.log(x));
}

console.log(bar());

Answer 1

Your code seems overly complicated. I think what you want is this (I didn't promisify mongoskin because it's not very well suited for that; see below):

export default class User {
  constructor() {
    this.db         = mongoskin.connect(...);
    this.collection = this.db.collection('users');
  }

  find (query = {}, options = {}) {
    return new Promise((resolve, reject) => {
      this.collection.find(query, options).toArray((err, items) => {
        if (err) return reject(err);
        resolve(items);
      });
    });
  }
}

I have to say that Mongoskin feels pretty outdated. It's a skin on top of the official mongodb driver, which is pretty decent nowadays (it supports promises out-of-the-box, for one, something that Mongoskin doesn't propagate).

If you do want to promisify, then I should say that the following is a promise anti-pattern:

return Promise.resolve().then(() => {
  return this.collection.findAsync(query, options);
}).then(...)

You can rewrite it to this:

return this.collection.findAsync(query, options).then(...);

However, the toArray() makes things difficult again, because for that you do need to create a new promise, so the code becomes something like this:

return this.collection.findAsync(query, options).then((cursor) => {
  return new Promise((resolve, reject) => {
    cursor.toArray((err, items) => {
      if (err) return reject(err);
      resolve(items);
    });
  });
});

Which doesn't look very pretty at all, hence my choice to not promisify and just use callbacks in this case (although I'm sure that Bluebird has some nice tools that may the above code easier to look at, but still...).