Mongoose validates all array items when one entry is updated

[lvkins]

Do you want to request a feature or report a bug?

Possibly a bug

What is the current behavior?

Document.set causes entire schema array validation.

If the current behavior is a bug, please provide the steps to reproduce.

When using the following schema:

const SectionSchema = new Schema({
	title: {
		type: String,
		required: true,
		maxlength: 24
	},
	state: {
		type: String,
		validate: function(v) {
			console.log(`@section '${this.title}' state is validating`)
			return true;
		}
	}
}, {_id: false});

const RootSchema = new Schema({
    name: {
		type: String,
		required: true
	},
    sections: [SectionSchema]
});

Updating a SectionSchema state by a dot notation path through the set and save triggers all RootSchema sections array items validate methods:

// Entries in the Root schema:
// { name: "Test1, sections: [{ title: "foo", state: ""}, { title: "bar", state: ""}, , { title: "boo", state: ""}] }

const doc = Root.findOne({name: "Test1"})
// Update first section state
doc.set("sections.0.state", "hello world", String);
// Commit modified-only changes
await doc.save({validateModifiedOnly: true});

// Console output (should've validate only updated field in this case)
// @section 'foo' state is validating
// @section 'bar' state is validating
// @section 'boo' state is validating

This is interesting, because updateOne behavior is slightly different and it just works fine while updating the same path:

const doc = Root.findOne({name: "Test1"})

// Update directly
await doc.updateOne({
    $set: { "sections.0.state": "john doe" }
}, { runValidators: true });

// Console output:
// @section 'foo' state is validating

I cannot make use of the updateOne because I need to utilize the save middleware.

What is the expected behavior?

When using Document.prototype.set to explicitly update a value, I believe that mongoose shouldn't wastefully validate unmodified array items.

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.

• mongodb: 3.6.4
• mongoose: 5.11.8
• nodejs: 14.10.0

[IslandRhythms]

const mongoose = require('mongoose');

const SectionSchema = new mongoose.Schema({
	title: {
		type: String,
		required: true,
		maxlength: 24
	},
	state: {
		type: String,
		validate: function(v) {
			console.log(`@section '${this.title}' state is validating`)
			return true;
		}
	}
}, {_id: false});

const RootSchema = new mongoose.Schema({
    name: {
		type: String,
		required: true
	},
    sections: [SectionSchema]
});
const Root = mongoose.model('Root', RootSchema);

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

  await Root.create({
    name: 'Test1',
    sections: [{title: 'foo', state: ""}, {title: 'bar', state: ""}, ,{title: "boo", state:""}],
  });
  console.log(user.name);
  const doc = await Root.findOne({name: "Test1"});
  //doc.set("sections.0.state", "hello world", String);
  //await doc.save({validateModifiedOnly: true});

  await doc.updateOne({
    $set: {"sections.0.state": "john doe"}}, {runValidators: true})
})();