How to populate field of an embedded document?

I have an OrderSchema, which contains "Invoice" as an embedded schema. I want to populate a field ("series") from the nested schema.

The schema looks like the following:

    const OrderSchema = new Schema({
        success: {
            type: Boolean,
        },
        invoice: {
            type: new Schema({
                series: {
                    // NEEDS TO POPULATE
                    type: Schema.Types.ObjectId,
                    ref: "Series",
                    required: true,
                },
                number: {
                    type: Number,
                    required: true,
                },
            }, { 
                _id: false,
                timestamps: false 
            }),
            required: true,
        },
    });

Here, I need to populate the path "invoice.series". How can I achieve this?

You can populate it like this

  OrderModel.find(query)
  .populate({ 
     path: 'invoice',
     populate: {
       path: 'series',
     } 
  })
  .exec(function(err, docs) {});

or optionally you can do this ...

OrderModel.find(query)
      .populate("invoice.series")
      .exec(function(err, docs) {});