`Model.hydrate` does not always cast Object ID values correctly

[asabhaney]

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

Bug (and backward breaking - looks like the regression was initially introduced in 5.12.4)

What is the current behavior?

The behaviour of Model.hydrate is inconsistent with how it casts String values for fields that should be ObjectIds.

• If no ref schema path option is specified, the hydration works as expected when an ID string is passed in.
• If the ref option is set, the hydration fails.

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

const assert = require('assert')
const mongoose = require('mongoose')
const { Schema } = mongoose

it('Calling `Model.hydrate` does not always cast Object ID values correctly', async () => {
   const bookSchema = new Schema({
      // Removing the `ref: 'author'` option causes the test to pass successfully
      author: { type: mongoose.Types.ObjectId, required: true, ref: 'author' }
   })

   const Book = mongoose.model('book', bookSchema)

   const book = Book.hydrate({
      author: '513bb18e268bb25016131ca6'
   })

   assert(book.author instanceof mongoose.Types.ObjectId)
})

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

node.js: 14.17.6
mongoose: 6.0.14
MongoDB: 4.4.6

[IslandRhythms]

I'm confused by your usage of ref

https://mongoosejs.com/docs/api.html#schematype_SchemaType-ref

It does not cause a problem for me when I do the following:

const assert = require('assert')
const mongoose = require('mongoose')
const { Schema } = mongoose

async function run() {
    await mongoose.connect('mongodb://localhost:27017/', {useNewUrlParser: true,
    useUnifiedTopology: true,});
    await mongoose.connection.dropDatabase();
    const authorSchema = new Schema({
        name: String
    });
   const bookSchema = new Schema({
      // Removing the `ref: 'author'` option causes the test to pass successfully
      author: { type: mongoose.Types.ObjectId, required: true, ref: 'author' }
   })

   const Book = mongoose.model('book', bookSchema);
   const Author = mongoose.model('author',  authorSchema);
  const entry = await Author.create({
       name: 'John'
   })

   const book = Book.hydrate({
      author: entry._id
   })

   assert(book.author instanceof mongoose.Types.ObjectId)
   console.log('done')
};

run();

[asabhaney]

In your example, if you change

const book = Book.hydrate({ author: entry._id })

to

const book = Book.hydrate({ author: entry.id }) // (id instead of _id)

then the test will fail, and that is the issue. A string representation of the _id is being passed in to hydrate, but should be cast to an ObjectId instance when a new mongoose doc is created.

[IslandRhythms]

https://mongoosejs.com/docs/guide.html#id

https://mongoosejs.com/docs/api.html#document_Document-id

id is suppose to be a string

[asabhaney]

I do understand id is supposed to be a string, but the issue I'm trying to communicate is about how Model.hydrate is designed to work. Perhaps I'm not being clear, so allow me to explain through an example.

Let's say you create a Book document, as you did above in your example. Now, you want to save that book record to a file or cache, or perhaps you need to transmit it over a network. Either way, to do so, you need to create a JSON representation of the data. But JSON doesn't have such a thing as an ObjectId, so your ObjectIds become stringified when you create a plain JSON object.

Later on, you are receiving or loading this JSON object, but now you want to use it as a mongoose doc (and you want your IDs to be ObjectIds again, and not strings, as they are when in plain JSON format). So you use Model.hydrate, which I believe is the intended solution for this particular use-case.

Upon using Model.hydrate, you expect that each of the fields in your mongoose doc are correctly typed to match the schema path definitions. And up until 5.12.4, this is how it worked, which is why I believe this is a bug and not the intended behavior.

I hope that provides more context and clarity, but if not, please let me know. Thanks in advance.

[IslandRhythms]

const assert = require('assert')
const mongoose = require('mongoose')
const { Schema } = mongoose

async function run() {
    await mongoose.connect('mongodb://localhost:27017/', {useNewUrlParser: true,
    useUnifiedTopology: true,});
    await mongoose.connection.dropDatabase();
    const authorSchema = new Schema({
        name: String
    });
   const bookSchema = new Schema({
      // Removing the `ref: 'author'` option causes the test to pass successfully
      author: { type: mongoose.Types.ObjectId, required: true, ref: 'author' }
   })

   const Book = mongoose.model('book', bookSchema);
       const Author = mongoose.model('author',  authorSchema);
        const entry = await Author.create({
        name: 'John'
    })

   const book = Book.hydrate({
      author: entry.id
   })

   assert(book.author instanceof mongoose.Types.ObjectId)
   console.log('done')
};

run();

npm install mongoose 5.12.3: passes
npm install mongoose@latest: fails