Mongoose attempting to cast subdocument schema to string

[wcarhart]

Do you want to request a feature or report a bug?
I think a bug, but may just be confused.

What is the current behavior?
I have the following schema with a subdocument:

const award = new mongoose.Schema({
  title: { type: String, required: true },
  issueDate: Date,
}, { _id : false, strict: 'throw' })

const profile = new mongoose.Schema({
  handle: { type: String, required: true, max: 30 },
  ...
  awards: [{ type: award }],
}, { strict: 'throw' })

const Profile = mongoose.model('profile', profile)

I am trying to PATCH the following data via my API on a model created via the above schema:

{
  "awards": [{
    "title": "test award",
    "date": "2022-03-08T18:13:36.433Z"
  }]
}

Using the following JavaScript code:

let updatedProfile = {
  handle: 'test',
  ...
  awards: [ { title: 'test award', date: '2022-03-08T18:13:36.433Z' } ]
}
// omitted try-catch for brevity
await (new Profile(updatedProfile)).validate()
await Profile.findOneAndUpdate(
  { handle: 'test' },
  updatedProfile,
  { upsert: true }
)

But, I get the error Error: Validation failed: awards: Cast to embedded failed for value "..." (type string) from the Profile.validate() step:

Error: Validation failed: awards: Cast to embedded failed for value "{ title: 'test award', date: '2022-03-08T18:13:36.433Z' }" (type string) at path "awards", awards.0: Cast to embedded failed for value "{ title: 'test award', date: '2022-03-08T18:13:36.433Z' }" (type string) at path "awards"
    at ValidationError.inspect (.../node_modules/mongoose/lib/error/validation.js:48:26)
    at internal/per_context/primordials.js:23:32
    at formatValue (internal/util/inspect.js:774:19)
    at inspect (internal/util/inspect.js:336:10)
    at formatWithOptionsInternal (internal/util/inspect.js:2006:40)
    at formatWithOptions (internal/util/inspect.js:1888:10)
    at console.value (internal/console/constructor.js:320:14)
    at console.warn (internal/console/constructor.js:353:61)
    at /Users/wcarhart/code/ethos/routes/api.js:154:12
    at processTicksAndRejections (internal/process/task_queues.js:93:5) {
  errors: {
    awards: CastError: Cast to embedded failed for value "{ title: 'test award', date: '2022-03-08T18:13:36.433Z' }" (type string) at path "awards"
        at DocumentArrayPath.cast (.../node_modules/mongoose/lib/schema/documentarray.js:483:19)
        at .../node_modules/mongoose/lib/model.js:4305:28
        at .../node_modules/mongoose/lib/helpers/promiseOrCallback.js:32:5
        at new Promise (<anonymous>)
        at promiseOrCallback (.../node_modules/mongoose/lib/helpers/promiseOrCallback.js:31:10)
        at Mongoose._promiseOrCallback (.../node_modules/mongoose/lib/index.js:1140:10)
        at Function.validate (.../node_modules/mongoose/lib/model.js:4254:23)
        at .../routes/api.js:152:18
        at processTicksAndRejections (internal/process/task_queues.js:93:5) {
      stringValue: `"{ title: 'test award', date: '2022-03-08T18:13:36.433Z' }"`,
      messageFormat: undefined,
      kind: 'embedded',
      value: "{ title: 'test award', date: '2022-03-08T18:13:36.433Z' }",
      path: 'awards',
      reason: [StrictModeError],
      valueType: 'string'
    },
    'awards.0': CastError: Cast to embedded failed for value "{ title: 'test award', date: '2022-03-08T18:13:36.433Z' }" (type string) at path "awards"
        at DocumentArrayPath.cast (.../node_modules/mongoose/lib/schema/documentarray.js:483:19)
        at DocumentArrayPath.cast (.../node_modules/mongoose/lib/schema/documentarray.js:402:17)
        at SchemaType.DocumentArrayPath.$embeddedSchemaType.cast (.../node_modules/mongoose/lib/schema/documentarray.js:75:29)
        at .../node_modules/mongoose/lib/model.js:4305:28
        at .../node_modules/mongoose/lib/helpers/promiseOrCallback.js:32:5
        at new Promise (<anonymous>)
        at promiseOrCallback (.../node_modules/mongoose/lib/helpers/promiseOrCallback.js:31:10)
        at Mongoose._promiseOrCallback (.../node_modules/mongoose/lib/index.js:1140:10)
        at Function.validate (.../node_modules/mongoose/lib/model.js:4254:23)
        at .../routes/api.js:152:18 {
      stringValue: `"{ title: 'test award', date: '2022-03-08T18:13:36.433Z' }"`,
      messageFormat: undefined,
      kind: 'embedded',
      value: "{ title: 'test award', date: '2022-03-08T18:13:36.433Z' }",
      path: 'awards',
      reason: [StrictModeError],
      valueType: 'string'
    }
  },
  _message: 'Validation failed'

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

What is the expected behavior?
I would not expect this data to fail validation. I've also tried creating a new Date() from awards[0].date but the same error occurred.

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.
Node
node --version: v14.14.0

Mongoose
node -e 'console.log(require("mongoose").version)': 6.2.4

MongoDB
v4.4 on DigitalOcean

[wcarhart]

I think I found the issue: the schema for Profile.awards[0] has a field called issueDate, not date, so it was a typo on my end. However, I don't think this error message did a great job at illuminating where the issue was?

[vkarpov15]

You're right that this error message isn't great. The "string" part is a mistake that we'll fix. Digging out the root cause for this error would involve either spotting the "date" property in the string description, or drilling down into the fact that the error for awards.0 has a reason property that contains a StrictModeError.