title: How to skip mongoose pre-save hook?
body: <p>I have a book model. Here's its schema</p>
  
  <pre><code>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();
  });
  </code></pre>
  
  <p>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 <code>Book.update()</code>, which skips the pre-save hook, but use <code>Book.findById(id).select('lowestPrice')</code> to find the book than update it. The problem was that I didn't want to select the <code>title</code> field, thus when it came to the pre-save hook, a <code>TypeError</code> occured for <code>this.title</code> was undefined. Are there ways to skip the pre-save hook?</p>