Populate in Mongoose doesn't work if I'm using Typescript Error: Schema hasn't been registered for model "Category"

[Eligio93]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

8.9.1

Node.js version

22.14.0

MongoDB server version

6.12.0

Typescript version (if applicable)

5

Description

I'm using NextJs 15 with TypeScript and Mongoose, but when I try to populate the Product fields with the category, I get the following error: Error: Schema hasn't been registered for model "Category". Use mongoose.model(name, schema). Also I've realized that if I comment out .populate() and then add it back when the server is already running, it works perfectly. So seems the problem is at the moment of compiling code.

Steps to Reproduce

This is the Product Schema:

import mongoose from "mongoose";
import { Schema } from "mongoose";
import ProductInterface from "@/interfaces/product.interface";

const ProductSchema = new Schema<ProductInterface>({
  name: { type: String, required: true },
  description: { type: String, required: true },
  brand: { type: String, required: true },
  price: { type: Number, required: true },
  images: [{ type: String, required: true }],
  category: { type: Schema.Types.ObjectId, ref: "Category", required: true },
  gender: { type: String, required: true },
  stock: { type: Number, required: true },
  rating: { type: Number, required: true, max: 5 },
  discount: { type: Number },
  isFeatured: { type: Boolean, required: true },
  views: { type: Number, required: true },
  isLive: { type: Boolean, required: true },
});

const Product =
  mongoose.models.Product ||
  mongoose.model<ProductInterface>("Product", ProductSchema);

export default Product;

This is my category Schema:

import mongoose from "mongoose";
import { Schema } from "mongoose";
import CategoryInterface from "@/interfaces/category.interface";

const CategorySchema = new Schema<CategoryInterface>({
  name: { type: String, required: true },
  description: { type: String, required: true },
  image:{type:String,required:true},
  isFeatured: { type: Boolean, required: true },
});

const Category =
  mongoose.models.Category ||
  mongoose.model<CategoryInterface>("Category", CategorySchema);

export default Category;

and this is my use case:

  await connectDB();
  const newArrivals/*: HydratedDocument<ProductInterface & { category: CategoryInterface }>[] */ = await Product.find({ isLive: true })
    .sort({ _id: -1 })
    .limit(6)
    .populate('category')
    .exec();

Expected Behavior

No response

[vkarpov15]

How are you importing these models? The most likely explanation is that you haven't imported the Category model when you're running the await Product.find().populate('category') query