猫鼬错误：“模型路径”_id“处的值”null“（类型字符串）强制转换为 ObjectId 失败......"-解网

问：

我目前正在创建简单的 CRUD 应用程序，让我可以创建产品并将其存储在 Mongo 数据库中。该应用程序运行良好，但当我尝试转到“/products/show”页面（或使用特定产品时）时，它不断抛出错误消息。

我真的不知道发生了什么，因为这是我第一次使用 Mongoose 和 MongoDB。该应用程序运行正常，这是应该的，但是即使屏幕上的所有内容都显示在屏幕上，此错误消息也会导致程序继续加载。

我的索引 .js 文件

const express = require('express');
const app = express();
const path = require('path');
const mongoose = require('mongoose');

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

mongoose.connect('mongodb://localhost:27017/farmStand', { useNewUrlParser: true, useUnifiedTopology: true })
    .then(() => {
        console.log("MONGO CONNECTION IS OPEN!");
    })
    .catch(err => {
        console.log("Oh no.. Mongo error");
        console.log(err);
    });

app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'ejs');

app.use(express.urlencoded({ extended: true }));

app.get('/products', async (req, res) => {
    const products = await Product.find({});
    res.render('products/index', { products });
});

app.get('/products/new', (req, res) => {
    res.render('products/new');
});

app.post('/products', async (req, res) => {
    const newProduct = new Product(req.body);
    await newProduct.save();
    console.log(newProduct);
    res.redirect(`/products/${newProduct._id}`);
});

// This is where the error is occuring.
app.get('/products/:id', async (req, res) => {
    try {
        const product = await Product.findById(req.params.id);
        res.render('products/show', { product });
    }
    catch (error) {
        console.log(error);
    }
});

app.listen(3000, () => {
    console.log("APP IS LISTENING ON PORT 3000");
});

我的 productSchema 文件

const mongoose = require('mongoose');

const productSchema = new mongoose.Schema({
    name: {
        type: String,
        required: true
    },
    price: {
        type: Number,
        required: true,
        min: 0
    },
    category: {
        type: String,
        lowercase: true,
        enum: ['fruit', 'vegetables', "dairy"]
    }
});

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

module.exports = Product;

我的 EJS '/show' 文件

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <meta name="viewport" content="width=device-width, initial-scale=1.0" />
        <title><%= product.name %></title>
    </head>
    <body>
        <h1><%= product.name %></h1>
        <ul>
            <li>Price: $<%= product.price %></li>
            <li>Category: <%= product.category %></li>
        </ul>
        <a href="/products">All products</a>
    </body>
</html>

错误消息

CastError: Cast to ObjectId failed for value "null" (type string) at path "_id" for model "Product"
    at ObjectId.cast (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/schema/objectid.js:250:11)
    at SchemaType.applySetters (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/schematype.js:1220:12)
    at SchemaType.castForQuery (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/schematype.js:1632:15)
    at cast (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/cast.js:356:32)
    at Query.cast (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/query.js:4910:12)
    at Query._castConditions (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/query.js:2232:10)
    at model.Query._findOne (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/query.js:2519:8)
    at model.Query.exec (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/query.js:4429:28)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async /Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/index.js:40:25 {
  stringValue: '"null"',
  messageFormat: undefined,
  kind: 'ObjectId',
  value: 'null',
  path: '_id',
  reason: BSONError: Argument passed in must be a string of 12 bytes or a string of 24 hex characters or an integer
      at new ObjectId (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/bson/lib/bson.cjs:2006:23)
      at castObjectId (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/cast/objectid.js:25:12)
      at ObjectId.cast (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/schema/objectid.js:248:12)
      at SchemaType.applySetters (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/schematype.js:1220:12)
      at SchemaType.castForQuery (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/schematype.js:1632:15)
      at cast (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/cast.js:356:32)
      at Query.cast (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/query.js:4910:12)
      at Query._castConditions (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/query.js:2232:10)
      at model.Query._findOne (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/query.js:2519:8)
      at model.Query.exec (/Users/nielskoop/Coding/UdemyCourse/MongoDB/38_mongoose-express/node_modules/mongoose/lib/query.js:4429:28),
  valueType: 'string',
  model: Model { Product }
}

我尝试过的解决方案

我在网上找不到太多关于这个主题的信息，而且可用的信息非常混乱。我尝试添加一个语句来检查给定的 id ，但这只会完全阻止程序工作。我还尝试将 Mongoose 给出的 ID 转换为一个简单的字符串，并将其存储在一个单独的变量中，以便我以后可以使用它，但这也完全阻止了程序的工作。ifisValid

所需解决方案

我想找出导致此错误的原因以及如何修复它。我有一种感觉，当我转到“/show”页面时，代码会继续运行并检查 Mongoose 中的新 ID 值，而该值不存在。然而，我可能完全错了。

提前致谢！

节点 .js mongoDB Express 猫鼬

app.get('/products/:id', async (req, res) => {
    try {
        const { id } = req.params;
        if (id.match(/^[0-9a-fA-F]{24}$/)) {
            const product = await Product.findById(id);
            res.render('products/show', { product });
        }
    }
    catch (error) {
        console.log(error);
    }
});

它不再抛出错误消息。我现在的问题是，这样的代码是否好，或者是否可以以某种方式改进？此外，页面会继续加载直到永恒，这是我眼中的一根刺。这是正常行为，还是不好？如果不好，我该如何解决？😊

0赞 jQueeny 9/6/2023 #2

你绝对不需要运行一个声明来制作你的工作。if (id.match...){...}findById(id)

错误消息告诉您：

Cast to ObjectId failed for value "null" (type string) at path "_id"

所以在这个代码中：

app.post('/products', async (req, res) => {
   const newProduct = new Product(req.body);
   await newProduct.save();
   console.log(newProduct);
   res.redirect(`/products/${newProduct._id}`); //< You are sending null
});

我怀疑在某些情况下，您的和猫鼬有些不太对劲，猫鼬没有创建产品，然后当您尝试重定向时会产生连锁反应。您认为您正在重定向到：const newProduct

res.redirect(`/products/${newProduct._id}`);
//            /products/64f7728ac8718d458e441283

但实际上，您正在重定向到：

res.redirect(`/products/${newProduct._id}`);
//            /products/null

所以在你的：req.params.idnull

app.get('/products/:id', async (req, res) => {
   try {
      const product = await Product.findById(req.params.id); //< req.params.id = null
   }
   //...
   //...
});

您需要一个块来找出产品创建何时失败。目前，您只是盲目地重定向。实现此更改：try/catchapp.post('/products'...)

app.post('/products', async (req, res, next) => {
   try{
      const newProduct = new Product(req.body);
      await newProduct.save();
      console.log(newProduct);
      res.redirect(`/products/${newProduct._id}`);
   } catch(err){
      console.log(err);
      next(err);
   }
});

否则，您的代码看起来不错，可能只是您实际发布的数据存在问题，导致产品无法创建。

猫鼬错误：“模型路径”_id“处的值”null“（类型字符串）强制转换为 ObjectId 失败......"

Mongoose error: "Cast to ObjectId failed for value "null" (type string) at path "_id" for model ... "