Mongoose: CastError: Cast to ObjectId failed for value “[object Object]” at path “_id”

10.9K Asked by AnushriSingh in Python , Asked on Jun 8, 2021

I am new to node.js, so I have a feeling that this will be something silly that I have overlooked, but I haven't been able to find an answer that fixes my problem. What I'm trying to do is create a path that will create a new child object, add it to the parent's array of children, then return the child object to the requester. The problem that I am running into is that if I pass the string id into findById, node crashes with

TypeError: Object {} has no method 'cast'

If I try to pass in an ObjectId instead, I get

CastError: Cast to ObjectId failed for value "[object Object]" at path "_id"

Here is a rough outline of my code:

var mongoose = require('mongoose'); 
var Schema = mongoose.Schema; 
var ObjectId = Schema.ObjectId; 
//Have also tried Schema.Types.ObjectId, mongoose.ObjectId 
mongoose.connect('mongodb://user:password@server:port/database'); 
app.get('/myClass/:Id/childClass/create', function(request, result) { 
var id = new ObjectId(request.params.Id); MyClass.findById(id).exec( function(err, myClass) { 
if (err || !myClass) { 
result.send("error: " + err + "
" +
JSON.stringify(id) || ("object '" + request.params.Id
+ "' not found: " + id)); 
return; 
} 
var child = ChildClass(); 
myClass.Children.addToSet(child); 
myClass.save(); result.send(child); 
}); 
});

If I execute this code with the path "/myClass/51c35e5ced18cb901d000001/childClass/create", this is the output of the code:

error: CastError: Cast to ObjectId failed for value "[object Object]" at path "_id" {"path":"51c35e5ced18cb901d000001","instance":"ObjectID","validators":[],"setters":[],"getters":[],"_index":null}

I've tried using findOne and passing in {_id:id} instead, but this appears to be exactly what findById does. I've tried the different classes for ObjectId that I've seen listed on other sites. I've tried calling ObjectId() like a function instead of a constructor and that returns undefined. At this point, I'm running out of ideas and it doesn't seem that googling for an answer is helping. Any ideas on what I'm doing wrong?

Also, as I said, I'm new to Node/Mongo/Mongoose/Express, so if there is a better way to accomplish my goal, please let me know. I appreciate all the feedback.

Answered by David EDWARDS

You can use the below-mentioned code to resolve casterror: cast to objectid failed for value.

My schema:

const product = new mongooseClient.Schema({ 

retailerID: { type: mongoose.SchemaTypes.ObjectId,

required: true, index: true } 

});

And then, when inserting:

retailerID: `${retailer._id}`

Your Answer

Answer (1)

Ranjana

It looks like you're encountering a CastError while trying to cast a value to an ObjectId in Mongoose. This error typically occurs when Mongoose expects a value to be of type ObjectId, but it's receiving something else, in this case, an object.

Here are a few things you can check to debug this issue:

Data Type Mismatch: Ensure that the value you're trying to assign to the _id field is compatible with ObjectId. ObjectId is typically a 24-character hexadecimal string or a 12-byte binary value.

Value Assignment: Double-check where you're assigning the value to the _id field. Make sure you're not mistakenly assigning an object instead of the expected ObjectId.

Schema Definition: Check your Mongoose schema definition for the model you're working with. Make sure the _id field is properly defined as type mongoose.Schema.Types.ObjectId.

Document Structure: If you're creating a new document, ensure that you're not inadvertently passing an object where an ObjectId is expected. For example, make sure you're not passing an entire object when creating a new document.

Debugging: Log the value that you're trying to assign to the _id field just before the error occurs. This will help you identify what exactly is causing the CastError.

Here's a simple example of a Mongoose schema definition with an _id field:

const mongoose = require('mongoose');

const Schema = mongoose.Schema;

const mySchema = new Schema({

  _id: {

    type: Schema.Types.ObjectId,

    auto: true, // This makes Mongoose generate the ObjectId automatically

  },

  // Other fields in your schema

});

const MyModel = mongoose.model('MyModel', mySchema);

module.exports = MyModel;

By ensuring that your code aligns with these points, you should be able to resolve the CastError. If you're still having trouble, feel free to provide more context or code snippets, and I can assist you further!

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