How to properly delete an orphaned reference in MongoDB?

So, I am building a small blog-like project in Node, and I am running into an issue with orphaned database references. I have two models in separate files that reference each other.

Here are my models:

// ./models/user   
Var UserSchema = mongoose.Schema({
  name: String,
  posts: [{type: mongoose.SchemaTypes.ObjectId, ref:'Post'}]
});

//  ./models/post
var PostSchema = mongoose.Schema({
  title:String,
  post_body: String,
  posted_by: mongoose.SchemaTypes.ObjectId
});

My question is when you delete say, a Post, how would you delete the reference in the User's post array? My thinking was I could create a middleware to run before the delete route and delete the reference in the User's post array before I actually delete the post. Would that be considered the best way to go about it? I found a post on Stack that uses a 'pre' function in the schema like this:

 // ./models/post
 PostSchema.pre('remove', function(next){
    this.model('User').remove({posts: this._id}, next);
 });

Here is the actual stack post: Automatically remove referencing objects on deletion in MongoDB . I could not get this work though. I did ,however, implement a custom middleware to delete the references, but feel it might not be best practice. Any tips/advice would be greatly appreciated. Thanks!