--- Introducing Version 4.0 of Mongoose, a popular NodeJS ODM for MongoDB, which includes exciting new features such as schema validation for update() and query middleware that enables pre and post hooks for count(), find(), findOne(), findOneAndUpdate(), and update(). This allows developers to define business logic for handling queries at the schema level, including running validators on update() operations. The new feature set also includes improved custom validator API, query middleware, and plugins to transform queries. With Mongoose 4.0, developers can make their applications more performant by allowing them to run validators without loading the whole document into memory, and automate tasks such as populate().