fix(document): allow calling push() with different $position arguments

[vkarpov15]

Fix #14244
Re: #4322

Summary

When we originally implemented push() with $position in #4322, we made it so that calling push() with different $position arguments would throw a sync error. This decision is not completely unreasonable because the MongoDB server doesn't support $push with different $position arguments. However, this decision is inconsistent with the rest of the array API: as a general rule, Mongoose arrays revert to just making the operation a $set on the entire array when Mongoose can't represent the user's desired update using atomic operators. With this PR, we will convert from atomic update to $set on the whole array if the user calls push() with multiple different $position arguments.

With this change, a modified version of the repro script from #14244 prints the following:

Mongoose: events.insertOne({ name: 'event object', arr: [ 'x', 'y', 'z' ], _id: new ObjectId("65a1512d0debc605ade502af"), __v: 0}, {})
true
[ 'x', 'y', 'z', '8' ]
[ 'x', 'y', 'z', '8' ]
[ 'x', 'y', 'b', 'z', '8' ]
[ 'x', 'c', 'y', 'b', 'z', '8' ]
Mongoose: events.updateOne({ _id: new ObjectId("65a1512d0debc605ade502af"), __v: 0 }, { '$set': { arr: [ 'x', 'c', 'y', 'b', 'z', '8' ] }, '$inc': { __v: 1 }}, {})

Modified version as follows:

const mongoose = require('mongoose');

mongoose.set('debug', true);
const util = require('util')
console.log(mongoose.version)
let Schema = mongoose.Schema
var eventSchema = new Schema({
  name: { type: String },
  arr: { type: Array, patch: true },
})

var Event = mongoose.model('Event', eventSchema)
async function run() {
  await mongoose.connect('mongodb://localhost:27017');
  let eventObj = new Event({ name: 'event object', arr: ['x', 'y', 'z'] })
  eventObj.save(function (err, eventObj) {
    console.log(util.types.isProxy(eventObj['arr']))
    eventObj['arr'].push('8')
    console.log(eventObj['arr'])
    eventObj['arr'].push({
      $each: ['a'],
      $position: 3
    })
    console.log(eventObj['arr'])
    eventObj['arr'].push({
      $each: ['b'],
      $position: 2
    })
    console.log(eventObj['arr'])
    eventObj['arr'].push({
      $each: ['c'],
      $position: 1
    })
    console.log(eventObj['arr']);

    eventObj.save();
  })
}
run();

Examples