How to create a copy of a document before saving with Mongoose?

Question

I have a document which user updates via web UI. I want to create a copy of the document and save it to the same collection before new changes are saved.

Here is the hook I am trying to consume:

PrototypeSchema.pre('save', function(next) {
  const protoCopy = new Prototype(proto.toObject())
  protoCopy.save()

  this.lastUpdateDate = new Date()
  next()
})

This causes infinite pre-save hook to be executed. How do I make a copy of the document and save both new version (as the same document) and previous one (as a new document)?

Answer 1

According to the pre-save middleware documentation , it does not run when updating a document but when inserting. For this you should use the pre-update. However, I am pretty sure that when the middleware runs the document already contains the changes so saving a copy of that document would be duplicating the updated document, and not saving a copy of the original document. I think the easier way may be to save the new document (with the old data) at the same place (controller or whatever) where you are updating the original document:

var originalId = "foo";
var changes = {foo: "bar"};

Prototype.findById(originalId, function(err, original){
    if (err) return { err };
    Prototype.insert(original, function(err){
        if (err) return { err };
        Prototype.findAndUpdate({_id: originalId}, changes, { new: true }, function(err, updated){
            return { err, updated };
        });
    });
});

EDIT:

About what I said (and the documentation says) about pre-save middleware not running when updating a document, I just thought I'm not sure if this depends on the version of Mongoose you're using. In any case, my code would work with any version.