How to populate the all sub schemas in a page without using findById?

Question

I have a user schema with the sub-schema called project and inside the project I have another schema called boq. How can I populate boqs and projects all in one page without using findById. I can populate projects by User.findById(req.user.id...etc but for projects, I cant use findById. anyway to populate boqs inside projects?

User schema:

var UserSchema = new Schema({
            company: String,
            projects: [
                {
                    type: mongoose.Schema.Types.ObjectId,
                    ref: "Project",
                }
            ],

});

Below is the project schema:

var projectSchema = new Schema({
        pname: String,
        boqs: [
            {
                type: mongoose.Schema.Types.ObjectId,
                ref: "Boq",
            }
        ],

});

And boq schema:

var boqSchema = new Schema({

        boqHeadIn: String,
        boqHead: String,
        boqIn: String,
        boqDesc: String,
        boqUnit: String,
        boqQty: Number,
        boqRate: Number,
        boqPrice: Number,

});