CastError: Cast to ObjectId failed for value “XXX” at path “_id” for model “Product”

问题


 enter code here
const express=require('express');

const router= express.Router();

const asyncHandler = require('express-async-handler');


const Product=require('../models/productModel');

router.get('/', asyncHandler(async (req,res)=>{
    const products=await Product.find({})
    res.send(products)
}));

router.get('/:id',asyncHandler(async(req,res)=>{
    const product=await Product.findById(req.params.id)
    
    if(product){
        res.json(product)
    }else{
        res.status(404).json({message:"product not found"})
    }`enter code here`
}));


    enter code here

module.exports=router`enter code here`

here i get data of products and product with id in postman or browser but if i enter wrong id it shows castError and in console log it shows it is internal server 500 error

回答1:

I will try to explain the error more extensively in case someone else happens to understand why.

_id's into Mongo are created in a specific way. You can check the docs where is explained the _id is an object called ObjectId and is compound by:

A 4-byte timestamp value, representing the ObjectId’s creation, measured in seconds since the Unix epoch
A 5-byte random value
A 3-byte incrementing counter, initialized to a random value

That implies that not just any value will be accepted.

When you do a query matching the _id, mongo expect an ObjectId(or at least, come type that could be parsed as string).

So if you try to use a bad _id, (for example -1 or XXX), the error will be thrown. Mongo can't parse -1 to ObjectId

If you are testing your application and you want to use a fake _id you need to generate a valid one.

Using mongoose you can call use this function: mongoose.Types.ObjectId().

The value return is a new _id generated, so it has a valid format.

来源：https://stackoverflow.com/questions/64755520/casterror-cast-to-objectid-failed-for-value-xxx-at-path-id-for-model-prod

标签

node.js

mongoose