#2, добавила модель товара

models/Product.js

+const mongoose = require('mongoose');
+
+const Schema = mongoose.Schema;
+
+const ProductSchema = new Schema({
+  author: {
+    type: Schema.Types.ObjectId,
+    ref: 'User',
+    required: true
+  },
+  category: {
+    type: Schema.Types.ObjectId,
+    ref: 'Category',
+    required: true
+  },
+  title: {
+    type: String,
+    required: true
+  },
+  description: {
+    required: true,
+    type: String
+  },
+  image: {
+    required: true,
+    type: String
+  },
+  price: {
+    required: true,
+    type: Number
+  }
+});
+
+const Product = mongoose.model("Product", ProductChema);
+
+module.exports = Product;