mongoose: getting unknown objectId when stored string instead of objectId - mongodb

Question

According to me when i pushed 'ABC' instead of objectId, It should show some error like
Cast to ObjectId failed for value "ABC" at path "likes".
but when i print that updated data i saw some unknown objectId in likes array
My question is, what is that unknown objectId(6a61736f6e20626f75726e65) and why it is generated
automatically
User Model
new Schema({
name: { type: String,required:true},
}, { usePushEach: true ,timestamp:true});
Feed Model
new Schema({
user: { type: Types.ObjectId, ref: 'user', required: true },
name: { type: String,default:null, trim: true },
likes: [{ type : Types.ObjectId, ref: 'user',}],
}, { usePushEach: true ,timestamp:true});
In Feed Schema likes have reference to User Schema
var data = await feed.findByIdAndUpdate(
postId,
{
$push: { likes: 'ABC' }
}
);
if(data){
var data = await feed.findById(postId);
console.log(data.likes);//["6a61736f6e20626f75726e65"]
}
OutPut:
["6a61736f6e20626f75726e65"]

Answer 1

Since you are pushing a String in likes which is not an ObjectId, you are getting this error.
Your schema clearly states that likes is an array of ObjectId:
likes: [{ type : Types.ObjectId, ref: 'user'}],
so you have to pass an ObjectId instead of user's name.
You have to do this:
// Whenever you are pushing value in `likes` `array`,
// you need to get the `ObjectId` of the user who liked the feed.
let userId = <userId_of_Ishwar>;
var data = await feed.findByIdAndUpdate(
postId,
{
$push: { likes: userId }
});