Print warning when schema type is a POJO with non-zero number of properties

[hardcodet]

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

Bug

What is the current behavior?

I have the following schema:

export const AuthorizationSchema = new mongoose.Schema({
    foo: {type: String, required: true },

    nested: {
        type: {
            xxx: { type: String, required: true },
            yyy: { type: String, required: true }
        },
        required: false
    },
    createdBy: {type: String, required: true }
});

If I save() an object I retrieved before, only the top-level properties are getting saved, not the nested one:

item.foo = "hello"; //will be saved
item.nested.xxx = "world" //won't be saved

Edit: This seems to be related to the type section I introduced to mark the nested type as optional. If I declare it like this, saving it works, but of course, the item is now required.

    nested: {
            xxx: { type: String, required: true },
            yyy: { type: String, required: true }
    },

Also, declaring the nested type as a schema of its own seems to work, so that's a fix that works:

nested: {
    type: NestedSchema,
    required: false
},

My understanding is that nested items in arrays are not automatically updated, but this isn't one.
A workaround would be to use markModified with the path, but I hope that's just a dirty hack ;)
I saw this reported in an earlier bug (see last comment on #6152) that was marked as resolved, but if that was fixed, it has resurfaced.

Mongoose version: 5.6.10 (I think), then upgraded to 5.6.11

[vkarpov15]

Your schema is incorrect. When you do nested: { type: { xxx: String } }, Mongoose considers that equivalent to nested: { type: {} } and makes nested a mixed path. You should do nested: { type: NestedSchema } like you suggested.

We should at least print a warning when this happens, it's a common mistake.

[hardcodet]

Thanks for the context, Valeri!

(I'll leave the ticket open since you labeled it - as far as I'm concerned, I'm all good :)

[vkarpov15]

We don't need this anymore, because in Mongoose 6 nested: { type: { xxx: String } } is equivalent to nested: { type: new Schema({ xxx: String }) }. So nested will be a subdocument.