How to skip mongoose pre-save hook?

I have a book model. Here's its schema

BookSchema = new Schema({
    title: String
    , lowestPrice: Number
});
BookSchema.path('title').required(true);
Bookchema.pre('save', function (next) {
    try {
        // chai.js
        expect(this.title).to.have.length.within(1, 50);
    } catch (e) {
        next(e);
    }
    next();
});

When a goods of a book is created, I have to update the book's lowest price if the goods' price is lower than the origin one. For I need to know the origin lowest price, I can't use Book.update(), which skips the pre-save hook, but use Book.findById(id).select('lowestPrice') to find the book than update it. The problem was that I didn't want to select the title field, thus when it came to the pre-save hook, a TypeError occured for this.title was undefined. Are there ways to skip the pre-save hook?