Inconsistent behavior default values nested paths using findOneAndUpdate with setDefaultsOnInsert

[curledUpSheep]

Mongoose version: 5.12.8

Reproduction script (drops existing test DB on local):

const mongoose = require('mongoose');

mongoose.set('useFindAndModify', false);

const schema = new mongoose.Schema({
  name: String,
  meta: {
    created: { type: Date, default: Date.now },
  },
});
const Model = mongoose.model('Test', schema);

run().catch(err => console.log(err));

async function run() {
  console.log("Mongoose version", mongoose.version);

  await mongoose.connect('mongodb://localhost:27017/test', {
    useNewUrlParser: true,
    useUnifiedTopology: true
  });
  await mongoose.connection.dropDatabase();

  const create1 = { name: 'create1' };
  const create2 = { name: 'create2', meta: {} };
  const findOneAndUpdate1 = { name: 'findOneAndUpdate1' };
  const findOneAndUpdate2 = { name: 'findOneAndUpdate2', meta: {} };

  const create1Doc = await Model.create(create1);
  const create2Doc = await Model.create(create2);

  const findOneAndUpdate1Doc = await Model.findOneAndUpdate(
    { name: 'findOneAndUpdate1' }, findOneAndUpdate1, { new: true, upsert: true, setDefaultsOnInsert: true });
  const findOneAndUpdate2Doc = await Model.findOneAndUpdate(
    { name: 'findOneAndUpdate2' }, findOneAndUpdate2, { new: true, upsert: true, setDefaultsOnInsert: true });

  console.log(create1Doc, create2Doc, findOneAndUpdate1Doc, findOneAndUpdate2Doc);
}

Console output:

Mongoose version 5.12.8
{
  meta: { created: 2021-05-11T10:44:24.773Z },
  _id: 609a6008d09bfddb908ebd6c,
  name: 'create1',
  __v: 0
} {
  _id: 609a6008d09bfddb908ebd6d,
  name: 'create2',
  meta: { created: 2021-05-11T10:44:24.789Z },
  __v: 0
} {
  meta: { created: 2021-05-11T10:44:24.794Z },
  _id: 609a6008d09bfddb908ebd6e,
  name: 'findOneAndUpdate1',
  __v: 0
} {
  meta: { created: 2021-05-11T10:44:24.799Z },
  _id: 609a6008d09bfddb908ebd6f,
  name: 'findOneAndUpdate2',
  __v: 0
}

DB:

 
    "_id" : ObjectId("609a6008d09bfddb908ebd6c"), 
    "meta" : {
        "created" : ISODate("2021-05-11T10:44:24.773+0000")
    }, 
    "name" : "create1", 
    "__v" : NumberInt(0)
}
{ 
    "_id" : ObjectId("609a6008d09bfddb908ebd6d"), 
    "name" : "create2", 
    "meta" : {
        "created" : ISODate("2021-05-11T10:44:24.789+0000")
    }, 
    "__v" : NumberInt(0)
}
{ 
    "_id" : ObjectId("609a6008d09bfddb908ebd6e"), 
    "name" : "findOneAndUpdate1", 
    "__v" : NumberInt(0), 
    "meta" : {
        "created" : ISODate("2021-05-11T10:44:24.794+0000")
    }
}
{ 
    "_id" : ObjectId("609a6008d09bfddb908ebd6f"), 
    "name" : "findOneAndUpdate2", 
    "__v" : NumberInt(0), 
    "meta" : {

    }
}

Expected behavior: Every document has meta.created.

Actual behavior: Every document returned by Mongoose has meta.created, but in DB findOneAndUpdate2 is missing meta.created.

[IslandRhythms]

const mongoose = require('mongoose');

mongoose.set('useFindAndModify', false);

const schema = new mongoose.Schema({
  name: String,
  meta: {
    created: { type: Date, default: Date.now },
  },
});
const Model = mongoose.model('Test', schema);

run().catch(err => console.log(err));

async function run() {
  console.log("Mongoose version", mongoose.version);

  await mongoose.connect('mongodb://localhost:27017/test', {
    useNewUrlParser: true,
    useUnifiedTopology: true
  });
  await mongoose.connection.dropDatabase();

  const create1 = { name: 'create1' };
  const create2 = { name: 'create2', meta: {} };
  const findOneAndUpdate1 = { name: 'findOneAndUpdate1' };
  const findOneAndUpdate2 = { name: 'findOneAndUpdate2', meta: {} };

  const create1Doc = await Model.create(create1);
  const create2Doc = await Model.create(create2);
  const findOneAndUpdate1Doc = await Model.findOneAndUpdate(
    { name: 'findOneAndUpdate1' }, findOneAndUpdate1, { new: true, upsert: true, setDefaultsOnInsert: true });
  const findOneAndUpdate2Doc = await Model.findOneAndUpdate(
    { name: 'findOneAndUpdate2' }, findOneAndUpdate2, { new: true, upsert: true, setDefaultsOnInsert: true });

  console.log(create1Doc, create2Doc, findOneAndUpdate1Doc, findOneAndUpdate2Doc);
  const db1 = await Model.findOne({name:'findOneAndUpdate1'}).lean();
  console.log(db1);
  const db2 = await Model.findOne({name:'findOneAndUpdate2'}).lean();
  console.log(db2);
}

[vkarpov15]

I took a closer look and this is expected behavior that there's no real workaround for. That's because setDefaultsOnInsert only sets defaults on paths that aren't modified in the update, and the below update technically updates meta.created by deleting any existing value of the key.

  const findOneAndUpdate2Doc = await Model.findOneAndUpdate(
    { name: 'findOneAndUpdate2' }, { meta: {} }, { new: true, upsert: true, setDefaultsOnInsert: true });

The only potential workaround Mongoose could to would be to add $setOnInsert like so: { $set: { meta: {} }, $setOnInsert: { 'meta.created': new Date() } }, but the MongoDB server doesn't support that. So there's no reasonable way for us to support this.

Instead, you should use Mongoose timestamps for this use case as shown below.

const mongoose = require('mongoose');

mongoose.set('debug', true);
mongoose.set('useFindAndModify', false);

const schema = new mongoose.Schema({
  name: String,
  meta: {
    created: { type: Date },
  },
}, { timestamps: { createdAt: 'meta.created' } });
const Model = mongoose.model('Test', schema);

run().catch(err => console.log(err));

async function run() {
  console.log("Mongoose version", mongoose.version);

  await mongoose.connect('mongodb://localhost:27017/test', {
    useNewUrlParser: true,
    useUnifiedTopology: true
  });
  await mongoose.connection.dropDatabase();

  const create1 = { name: 'create1' };
  const create2 = { name: 'create2', meta: {} };
  const findOneAndUpdate1 = { name: 'findOneAndUpdate1' };
  const findOneAndUpdate2 = { name: 'findOneAndUpdate2', meta: {} };

  const create1Doc = await Model.create(create1);
  const create2Doc = await Model.create(create2);
  const findOneAndUpdate1Doc = await Model.findOneAndUpdate(
    { name: 'findOneAndUpdate1' }, findOneAndUpdate1, { new: true, upsert: true, setDefaultsOnInsert: true });
  const findOneAndUpdate2Doc = await Model.findOneAndUpdate(
    { name: 'findOneAndUpdate2' }, findOneAndUpdate2, { new: true, upsert: true, setDefaultsOnInsert: true });

  console.log(create1Doc, create2Doc, findOneAndUpdate1Doc, findOneAndUpdate2Doc);
  const db1 = await Model.findOne({name:'findOneAndUpdate1'}).lean();
  console.log(db1);
  const db2 = await Model.findOne({name:'findOneAndUpdate2'}).lean();
  console.log(db2);
}