Promise.all返回双精度数组

Question

In my node Router I have the following:

router.get("/single-base/:id", (req, res) => {
Base.find({ _id: req.params.id })
    .then(bases => {
        let basefetches = [];

        for (let base of bases) {
            basefetches.push(BaseUser.find({ baseId: req.params.id }));
        }
        return Promise.all(basefetches).then(users =>
            res.json(users.map(user => user.serialize()))
        );
    })
    .catch(err => {
        console.error(err);
        res.status(500).json({ message: "Internal server error" });
    });
});

when console logging return Promise.all(basefetches).then(users => console.log(users)) I receive:

[ [ { created: 2018-08-27T21:37:42.151Z,
  _id: 5b846f268cb4481264298f82,
  userId: 'tester2',
  baseId: 5b81528e1314da25bc498085,
  acceptedMembership: false,
  isCreator: false,
  __v: 0 } ] ]

I have the exact same method in another place, and it returns only an empty array (this array should be empty in the beginning as well). Why/when/how is this pushing an array into another array, how do I solve this so that the users.map does not throw:

TypeError: Cannot read property 'push' of undefined
at Base.find.then.bases

EDIT : I believe this has to do with the BaseUser.find({}) method. When console logging: Promise.all(basefetches).then(users => console.log(users)); I get the following:

{ created: 2018-08-25T12:43:02.640Z,
  _id: 5b81528e1314da25bc498085,
  creatorId: 5b7efd4db3036a13601ad8d7,
  title: 'testBase1',
  __v: 0 }
[ [ { created: 2018-08-27T21:37:42.151Z,
      _id: 5b846f268cb4481264298f82,
      userId: 'tester2',
      baseId: 5b81528e1314da25bc498085,
      acceptedMembership: false,
      isCreator: false,
      __v: 0 } ] ]

I

Answer 1

Looks like MongoDB data. And if BaseUser.find() uses MongoDB's db.collection.find() , then it returns a cursor (hence the conversion to array at this level I guess).

If the baseId is intended to be unique (ie you expect one result at the most), you might want to use db.collection.findOne() instead.

However, I don't understand why you wrap

basefetches.push(BaseUser.find({ baseId: req.params.id }));

in a loop over bases , since bases is not used at all in the loop. Seems like you just repeat the exact same query yielding the exact same result for as many bases as you got.

Anyway: one array because of find() , and one because of the promises-slash-loop-over- bases .