mongoose get db value in pre-save hook

Question

I want to know what the 'clean' value of a dirty prop is in a pre-save mongoose hook like this:

UserSchema.pre('save', function(next) {
    var user = this;

    if (user.isModified('password')){
       //i want to know what the value of user.password was before it was changed
    }
    next()
}

Is it possible to look up the old value without looking it up in the db?

Answer 1

By default, the old values are not stored. You would have to do is track the old data with a post init hook (a mongoose feature).

What we do is attach copy of the original document to all items pulled from MongoDB. We have this code for each schema we need to get pre-dirty data for comparison:

schema.post( 'init', function() {
    this._original = this.toObject();
} );

NodeJS is pretty efficient, and does copy on write when possible, so you don't see double the memory consumption unless you modify the entire document. Only then does _original actually consume double the memory.

Answer 2

So in a pre-save hook, from what I can tell by reading this section of the source code, I don't think the previous value is stored anywhere. So you'll have to load the document from mongodb to get it.

However, you might want to use the virtuals mechanism instead of a pre-save hook to store the old value before changing it to the new value.

var virtual = schema.virtual('password');
virtual.set(function (v) {
  var this._oldPassword = this.password;
  return v;
});

Experiment with something along those lines and see if you can make something work suitably.