Nested population restoration on hydration a model

[yamaha252]

Prerequisites

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

Mongoose version

8.9.1

Node.js version

20.16.0

MongoDB server version

5.0.2

Typescript version (if applicable)

5.7.2

Description

On hydrating (with enabled hydratedPopulatedDocs option) a model has deep nested populated data, on second and next levels it applies in a raw condition without hydration.

Steps to Reproduce

const ArticleSchema = new Schema({
  title: {
    type: String
  }
});

const StorySchema = new Schema({
  title: {
    type: String
  },
  article: {
    type: Schema.Types.ObjectId,
    ref: 'Article'
  }
});

const UserSchema = new Schema({
  name: String,
  stories: [{
    type: Schema.Types.ObjectId,
    ref: 'Story'
  }]
});

db.deleteModel(/User/);
db.deleteModel(/Story/);
db.deleteModel(/Article/);

const User = db.model('User', UserSchema);
const Story = db.model('Story', StorySchema);
const Article = db.model('Article', ArticleSchema);

const article = await Article.create({ title: 'Cinema' });
const story1 = await Story.create({ title: 'Ticket 1', article });
const story2 = await Story.create({ title: 'Ticket 2' });

await User.create({ name: 'Alex', stories: [story1, story2] });

const populated = await User.findOne({ name: 'Alex' }).populate({
  path: 'stories',
  populate: ['article']
}).lean();

const hydrated = User.hydrate(
  JSON.parse(JSON.stringify(populated)),
  null,
  { hydratedPopulatedDocs: true }
);

assert.ok(hydrated.populated('stories'));

assert.ok(hydrated.stories[0].populated('article'));
assert.equal(hydrated.stories[0].article._id.toString(), article._id.toString());
assert.ok(typeof hydrated.stories[0].article._id === 'object');
assert.ok(hydrated.stories[0].article._id instanceof mongoose.Types.ObjectId);
assert.equal(hydrated.stories[0].article.title, 'Cinema');

assert.ok(!hydrated.stories[1].article);

Virtuals populated hydration:

const ArticleSchema = new Schema({
  title: {
    type: String
  }
});

const StorySchema = new Schema({
  userId: {
    type: Schema.Types.ObjectId,
    ref: 'User'
  },
  title: {
    type: String
  },
  article: {
    type: Schema.Types.ObjectId,
    ref: 'Article'
  }
});

const UserSchema = new Schema({
  name: String
});

UserSchema.virtual('stories', {
  ref: 'Story',
  localField: '_id',
  foreignField: 'userId'
});

db.deleteModel(/User/);
db.deleteModel(/Story/);
db.deleteModel(/Article/);

const User = db.model('User', UserSchema);
const Story = db.model('Story', StorySchema);
const Article = db.model('Article', ArticleSchema);

const article = await Article.create({ title: 'Cinema' });
const user = await User.create({ name: 'Alex' });
await Story.create({ title: 'Ticket 1', userId: user._id, article });
await Story.create({ title: 'Ticket 2', userId: user._id });

const populated = await User.findOne({ name: 'Alex' }).populate({
  path: 'stories',
  populate: ['article']
}).lean();

const hydrated = User.hydrate(
  JSON.parse(JSON.stringify(populated)),
  null,
  { hydratedPopulatedDocs: true }
);

assert.ok(hydrated.populated('stories'));

assert.ok(hydrated.stories[0].populated('article'));
assert.equal(hydrated.stories[0].article._id.toString(), article._id.toString());
assert.ok(typeof hydrated.stories[0].article._id === 'object');
assert.ok(hydrated.stories[0].article._id instanceof mongoose.Types.ObjectId);
assert.equal(hydrated.stories[0].article.title, 'Cinema');

assert.ok(!hydrated.stories[1].article);

Expected Behavior

Populated properties should be hydrated on all nested levels