嵌套MongoDB模式

Question

I've been learning MongoDB from their online Webinar hosted on their website and I'm trying to link Products to a Category (eg. iPhone belongs to Category Mobiles which has ancestors such as Electronics ), however while nesting I'm getting the following error:

MongooseError: Schema hasn't been registered for model "Category".
Use mongoose.model(name, schema)

I saw several questions, by writing Schema.ObjectId and Schema.Types.ObjectId, but I get Cast Error to ObjectId on firing an insert(save) query.

There are few more questions related to these:

1. How do I make sure, while adding a Product, I also add the Category it's linked to?
2. What would be a best practice for such kind of scenario (to add subdocuments or reference Schemas)?

PFB Model files, I have written Controller files on top of that in order to perform CRUD operations:

category.js

var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var categorySchema = new Schema({
  _id: { type: String },
  parent: {
    type: String,
    ref: 'Category'
  },
  ancestors: [{
    type: String,
    ref: 'Category'
  }]
});

module.exports.categorySchema = categorySchema;

products.js

var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var Category = require('./category');
var fx = require('./fx');

var productSchema = new mongoose.Schema({
  name: { type: String, required: true },
  // Pictures must start with "http://"
  pictures: [{ type: String, match: /^http:\/\//i }],
  price: {
    amount: {
      type: Number,
      required: true,
      set: function(v) {
        this.internal.approximatePriceUSD =
          v / (fx()[this.price.currency] || 1);
        return v;
      }
    },
    // Only 3 supported currencies for now
    currency: {
      type: String,
      enum: ['USD', 'EUR', 'GBP'],
      required: true,
      set: function(v) {
        this.internal.approximatePriceUSD =
          this.price.amount / (fx()[v] || 1);
        return v;
      }
    }
  },
  category: { type: Schema.ObjectId,ref: 'Category'},
  internal: {
    approximatePriceUSD: Number
  }
});

//var schema = new mongoose.Schema(productSchema);

var currencySymbols = {
  'USD': '$',
  'EUR': '€',
  'GBP': '£'
};

/*
 * Human-readable string form of price - "$25" rather
 * than "25 USD"
 */
productSchema.virtual('displayPrice').get(function() {
  return currencySymbols[this.price.currency] +
    '' + this.price.amount;
});

productSchema.set('toObject', { virtuals: true });
productSchema.set('toJSON', { virtuals: true });

module.exports = mongoose.model("Product", productSchema);

Example Output Structure of a Product:

{
    "_id": "**autogeneratedByMongo",
    "name":"iPhone",
    "category":{
        "_id":"Mobiles", 
        "ancestors":["Electronics","Mobiles"]
    }
    ....
}

Answer 1

Change the value of the type key to mongoose.Schema.Types.ObjectId it will make link to that perticular ObjectId to which you want to refer and with help of populate you can make call to whole parent schema by .populate('parent') .

For more info of I reffer to this :- populate

Thanks.