nodejs Promise.all在一些猫鼬的承诺上返回null

Question

i am passing array of mongoose promises and for some reason sometimes customerFindPromise return null, and sometimes it return the requested object. am i doing something wrong here

******************** START result0: null result END ********************
 ******************** START result1: { _id: 5a18a637346826574416a588,
doc_fname: 'Bob',
doc_lname: 'Smith',
numOfCases: 1,
__v: 0 } result END ********************
******************** START result2: {"n":1,"ok":1} result END ********************

Code

var customer = {
    doctor_id: 5a18a637346826574416a588,
    cust_fname: 'dfsdf',
    cust_lname: 'sdasd',
    case_type: 'Crowns',
    _id: 5a1cd19438f14164b0087753 
}
test(customerCase);
async function test(customerCase) {

    console.log("******************** customerCaseDelete: "+ customerCase._id +" ********************");
    var _id = customerCase._id;
    var doctor_id = customerCase.doctor_id;
    var query = {_id:_id};

    const customerFindPromise = CustomerCases.findById(_id);
    const customerRemovePromise = CustomerCases.remove(query);
    const doctorUpdatePromise = Doctors.findOneAndUpdate({_id:doctor_id},{'$inc': {'numOfCases': -1}},{new:true});

    await Promise.all([customerFindPromise,doctorUpdatePromise,customerRemovePromise])
      .then((result) => {
        console.log("******************** START result0: "+ result[0] +" result END ********************");
        console.log("******************** START result1: "+ result[1] +" result END ********************");
        console.log("******************** START result2: "+ result[2] +" result END ********************");
        res.json(result);
      }).catch((err) => {
          console.log("******************** START err: "+ err +" err END ********************");
         throw err;
      });
}

Answer 1

The functions you are running are asynchronous and won't always run in order. Promise.all does not change the execution order of the promises either, it just waits for them all to be resolved.

Sometimes CustomerCases.remove will execute and resolve before CustomerCases.findById so null resolves when the document has been removed first.

Wait for the promises to resolve serially before executing the next query, seeing as you are using async / await it's fairly simple to add:

try{
  let find = await CustomerCases.findById(_id)
  console.log(`find: ${find}`)
  let update = await CustomerCases.remove(query)
  console.log(`update: ${update}`)
  let remove = await Doctors.findOneAndUpdate({_id:doctor_id},{'$inc': {'numOfCases': -1}},{new:true})
  console.log(`remove: ${update}`)
  res.json([find, update, remove])
} catch(err) {
  console.error(err)
  throw err // next(err)?
}

Try bluebirds Promise.each if you need a serial execution helper.