How does the Dirty Checking mechanism work in Hibernate?

The Dirty Checking mechanism in Hibernate is responsible for tracking changes in entity objects that are in the session (persistence context). When the session is open, Hibernate saves the state of loaded objects. Before performing a save operation (flush), it compares the current state of the objects with the previously saved state.

If changes are detected (the object is "dirty"), Hibernate generates the appropriate SQL queries to update the data in the database.

This allows automatic synchronization of the in-memory object state with the database without the need to explicitly call update methods.

Example:

val session = sessionFactory.openSession()
session.beginTransaction()

val user = session.get(User::class.java, userId)
user.name = "New Name"  // Change the field

session.flush()  // Hibernate detects the change and performs an UPDATE

session.transaction.commit()
session.close()

Thus, Dirty Checking simplifies working with objects and ensures data integrity.