Cast to Number failed for value "NaN"

so, the problem is that I’m trying to add reviews for the related product. But whenever I tried to hit API through Postman it gave me an error

ValidationError: Product validation failed: rating: Cast to Number failed for value "NaN" (type number) at path "rating"
[0]     at Document.invalidate (E:\Web\Shop.co\node_modules\mongoose\lib\document.js:3197:32)
[0]     at model.$set (E:\Web\Shop.co\node_modules\mongoose\lib\document.js:1456:12)
[0]     at model.set [as rating] (E:\Web\Shop.co\node_modules\mongoose\lib\helpers\document\compile.js:205:19)
[0]     at E:\Web\Shop.co\backend\controller\productController.js:108:20
[0]     at process.processTicksAndRejections (node:internal/process/task_queues:95:5)

This is the Product Schema

const mongoose = require("mongoose");

const reviewSchema = mongoose.Schema(
  {
    name: { type: String, required: true },
    rating: { type: Number, required: true, default: 0 },
    comment: { type: String, required: true },
    user: {
      type: mongoose.Schema.Types.ObjectId,
      required: true,
      ref: "User",
    },
  },
  {
    timestamps: true,
  }
);

const productSchema = mongoose.Schema(
  {
    user: {
      type: mongoose.Schema.Types.ObjectId,
      required: true,
      ref: "User",
    },

    name: {
      type: String,
      required: true,
    },
    image: {
      type: String,
      required: true,
    },
    brand: {
      type: String,
      required: true,
    },
    category: {
      type: String,
      required: true,
    },
    description: {
      type: String,
      required: true,
    },
    price: {
      type: Number,
      required: true,
      default: 0,
    },
    review: [reviewSchema],
    rating: {
      type: Number,
      required: true,
      default: 0,
    },
    numReviews: {
      type: Number,
      required: true,
      default: 0,
    },
    countInStock: {
      type: Number,
      required: true,
      default: 0,
    },
  },
  {
    timestamps: true,
  }
);

const Product = mongoose.model("Product", productSchema);

module.exports = Product;

and this is the createReview function in the Product Controller

const createReview = asyncHandler(async (req, res) => {
  const { rating, comment } = req.body;
  const product = await Product.findById(req.params.id);
  if (product) {
    const alreadyReviewed = product.review.find(
      (r) => r.user.toString() === req.user._id.toString()
    );

    if (alreadyReviewed) {
      res.status(400).json({ message: " Product already reviewed" });
      throw new Error("Product already reviewed");
    }

    const reviews = {
      name: req.user.name,
      rating: Number(rating),
      comment,
      user: req.user._id,
    };
    product.review.push(reviews);

    product.numReviews = product.review.length;
    product.rating =
      product.review.reduce((item, acc) => item.rating + acc, 0) /
      product.review.length;

    await product.save();
    res.status(100).json({ message: " Review Added" });
  } else {
    res.status(400).json({ message: " Product not found" });
    throw new Error("Product not found");
  }
});

routes are

router.route("/:id/reviews").post(protect, createReview);

although the rating is defined as Number type and given Number during review creation, it still gives NaN error.

If I’m wrong or my code is wrong, please give me advice.

>Solution :

The error occurs because the reduce function is not correctly summing up the ratings of the reviews.

To fix this, you need to adjust the calculation of the product’s rating by correctly summing up the ratings of all reviews. Here’s the corrected version of your createReview function

const createReview = asyncHandler(async (req, res) => {
  const { rating, comment } = req.body;
  const product = await Product.findById(req.params.id);
  
  if (product) {
    const alreadyReviewed = product.review.find(
      (r) => r.user.toString() === req.user._id.toString()
    );

    if (alreadyReviewed) {
      res.status(400).json({ message: "Product already reviewed" });
      throw new Error("Product already reviewed");
    }

    const review = {
      name: req.user.name,
      rating: Number(rating),
      comment,
      user: req.user._id,
    };
    
    product.review.push(review);
    product.numReviews = product.review.length;

    // Calculate new average rating
    const totalRating = product.review.reduce((acc, item) => acc + item.rating, 0);
    product.rating = totalRating / product.review.length;

    await product.save();
    res.status(200).json({ message: "Review Added" });
  } else {
    res.status(404).json({ message: "Product not found" });
    throw new Error("Product not found");
  }
});