Add option to merge rather than overwrite schema-level `populate()` options

Prerequisites

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

Issue

hi, i have two schemas with below descriptions

User Schema

class User {
    @Prop() _id: number;
    @Prop() events: object; // it has two keys : create and delete
}

Custom Schema

class Custom {
    @Prop() _id: number;
    @Prop() user_id: number
}

CustomSchema.virtual('user' , {
  ref: 'user',
  localField: 'user_id',
  foreignField: '_id',
  options: {
      match: {
          'events.delete': null
      }
  }
})

custom schema has relation with user which is defined via a virtual.

How to produce problem

run this query :

custom.findOne({ _id:1 }).populate({ path: 'user, match: {'events.create': {$ne : null } } }).exec();

Expected behavior

populate user if events.delete is null and events.create is not null

Result

populate user if events.create is not null

What is the problem?

match defined in populate overwrites match defined in virtual. how to append match defined in populate with match defined in virtual?

thanks.

[vkarpov15]

We should add an option to merge rather than overwrite properties in populate().

[vkarpov15]

Right now we don’t have an easy workaround. The best option would be to store the schema-level match as a variable, and merge it manually:

const mongoose = require('mongoose');

const testSchema = new mongoose.Schema({
  name: String,
  events: {}
});

const otherSchema = new mongoose.Schema({
  userId: {type: mongoose.Schema.Types.ObjectId, ref: 'Test'}
}, {toObject: {virtuals: true}});

const userVirtualMatch = { 'events.delete': null };
otherSchema.virtual('user', {
  ref: 'Test',
  localField: 'userId',
  foreignField: '_id',
  options: { match: userVirtualMatch}
});

const Test = mongoose.model('Test', testSchema);

const Other = mongoose.model('Other', otherSchema);

async function run() {
  await mongoose.connect('mongodb://localhost:27017');
  await mongoose.connection.dropDatabase();

  const entry = await Test.create({
    name: 'Test',
    events: { delete: null, create: 'hi'}
  });

  const other = await Other.create({
    userId: entry._id
  });
  await Other.create();


  const result = await Other.findOne({ _id: other._id }).populate({path: 'user', match: {...userVirtualMatch, 'events.create': {$ne: null}}});
  console.log(result);
  console.log(result.user[0].events);
}

run();