Java.Hibernate.Beginner.How do you retrieve an object by its ID?

You retrieve an object by its primary key (ID) using either:
1️⃣ session.get() — recommended for most use cases, or
2️⃣ session.load() — advanced use cases.

🔹 Using session.get()

• Loads the entity immediately from the database or session cache.
• Returns the entity or null if no matching row is found.

Example:

Session session = sessionFactory.openSession();

User user = session.get(User.class, 1L); // fetch User with ID 1

if (user != null) {
    System.out.println("User: " + user.getUsername());
} else {
    System.out.println("User not found!");
}

session.close();

🔹 Using session.load()

• Returns a proxy without hitting the database immediately (lazy load).
• Only fetches data from DB if you actually access a property.
• Throws ObjectNotFoundException if no matching row exists.

Example:

Session session = sessionFactory.openSession();

User user = session.load(User.class, 1L); // returns proxy

System.out.println(user.getUsername());   // triggers DB fetch

session.close();

🔹 Key differences:

Method	Behavior	Null handling
get()	Eager: hits DB or cache immediately	Returns null if not found
load()	Lazy: returns proxy	Throws ObjectNotFoundException if entity missing

🔹 Important note:
✅ Both methods return an object in persistent state if found.
✅ Using get() is safer and more common in CRUD apps.
✅ Using load() can be efficient for lazy loading, but be careful about exceptions if the entity doesn’t exist.

✅ Key takeaway:
Use session.get(Entity.class, id) to eagerly fetch an object by its primary key, or session.load() for lazy-loading a proxy when you know the entity must exist.