getters array in virtualtype for "id" virtual is not deduped

[kmonagle]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

7.4.0

Node.js version

14.x

MongoDB server version

4.4

Typescript version (if applicable)

No response

Description

In Mongoose 5 the getters array for the "id" virtual was deduped. In Mongoose 6+ this no longer happens.

In Mongoose 6+, If models are repeatedly recreated, a new idGetter is added to the getters array with each model recreation. In my app, after a load test, the "id" getters array can grow to thousands of redundant idGetter functions. We use lean virtuals, so those thousands of functions are executed for every new object, and performance is severely degraded after a while.

Use case: we hot load and dynamically recreate models very frequently in our app.

In Mongoose 5 when a model was compiled there was a check to ensure that redundant functions didn't get added to the "id" virtual getter array:

Document.prototype.$__setSchema = function(schema) {
  schema.plugin(idGetter, { deduplicate: true });

Schema.prototype.plugin = function(fn, opts) {
  if (typeof fn !== 'function') {
    throw new Error('First param to `schema.plugin()` must be a function, ' +
      'got "' + (typeof fn) + '"');
  }

  if (opts && opts.deduplicate) {
    for (const plugin of this.plugins) {
      if (plugin.fn === fn) {
        return this;
      }
    }
  }
  this.plugins.push({ fn: fn, opts: opts });

  fn(this, opts);
  return this;
};

This check does not appear to exist in 6+, so the array can grow dramatically with redundant functions when models are regularly recreated.

Steps to Reproduce

const mongoose = require("mongoose")

const nameSchema = new mongoose.Schema({"name" : {
  "type" : "String"
}});

const Name = mongoose.model('Name', nameSchema);
console.log(mongoose.models);


for(let i = 0;i<10;i++){
  mongoose.model('Name', nameSchema);
  delete mongoose.models['Name'];
}

I added some console output in the mongoose source code, Virtualtype get method:

VirtualType.prototype.get = function(fn) {
  this.getters.push(fn);
  console.log("virtual path: ", this.path);
  console.log("getters size: ", this.getters.length);
  console.log("getters: ", this.getters);
  return this;
};

The output of the last few iterations of the loop in the script above show the "id" getters array growing with duplicate idGetter functions:

virtual path:  id
getters size:  8
getters:  [
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter]
]
autoIdGetter:  true
adding ID getter 
virtual path:  id
getters size:  9
getters:  [
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter]
]
autoIdGetter:  true
adding ID getter 
virtual path:  id
getters size:  10
getters:  [
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter],
  [Function: idGetter]
]

Expected Behavior

I'd expect Mongoose to do a 5.x-type sanity check to prevent duplicate functions from proliferating in virtual getter arrays. Something like this would fix the issue:

VirtualType.prototype.get = function(fn) {

  for (const getter of this.getters) {
     if (getter === fn) {
       return this;
     }
  } 

  this.getters.push(fn);
  return this;
};

[IslandRhythms]

const mongoose = require('mongoose');

const nameSchema = new mongoose.Schema({"name" : {
  "type" : "String"
}});

const Name = mongoose.model('Name', nameSchema);
console.log(mongoose.models);
console.log(Name.schema.virtuals)

for(let i = 0;i<10;i++){
  mongoose.model('Name', nameSchema);
  delete mongoose.models['Name'];
}

console.log(Name.schema.virtuals);