Schema plugins not applied to subdocuments

I have the following Mongoose plugin to handle some common JSON conversion:

'use strict';

/**
 * Default toJSON implementation for mongoose schema's
 */
module.exports = function toJsonPlugin(schema) {

  //NOTE: this plugin is actually called *after* any schema's
  //custom toJSON has been defined, so we need to ensure not to
  //overwrite it. Hence, we remember it here and call it later
  let transform;
  if (schema.options.toJSON && schema.options.toJSON.transform) {
    transform = schema.options.toJSON.transform;
  }

  //Set toJSON handler
  schema.options.toJSON = {
    transform(doc, ret) {

      //Delete version and set ID
      delete ret.__v;
      if (ret._id) {
        ret.id = ret._id.toString();
        delete ret._id;
      }

      //Call custom transform if present
      if (transform) {
        transform(doc, ret);
      }
    }
  };
};

This works great, and is applied on all my models. However, sub document schema’s don’t seem to inherit the behaviour for some reason.

For example, I have:

let NoticeSchema = new Schema({
  title: String,
  type: String,
  message: String,
  startDate: Date,
  endDate: Date,
  isEnabled: Boolean
});

This is a schema for a sub document, e.g.:

let ClubSchema = new Schema({
  //...
  notices: [NoticeSchema],
  //...
});

However, the outputted JSON for the club includes _id’s for the notices, and I have to explicitly define a toJSON handler on the notice schema for it to work as intended:

NoticeSchema.options.toJSON = {
  transform(doc, ret) {
    ret.id = ret._id.toString();
    delete ret._id;
  }
};

Is this intentional or a bug? I would assume plugins for schema’s apply to all schema’s, also sub document schema’s.

This is with 4.5.0.

[vkarpov15]

@Jeff-Lewis in 4.6.3 schemas created implicitly for document arrays will have a $implicitlyCreated field.

[vkarpov15]

@Jeff-Lewis I think mongoose only creates a new schema implicitly for document arrays. We can definitely mark those schemas with a property to make it easier to filter those out