What are lazy and eager fetching in Hibernate 7 and how do you avoid the N+1 problem?

// LAZY (default for @OneToMany):
@OneToMany(mappedBy="customer", fetch=FetchType.LAZY)
private List<Order> orders;

// N+1 PROBLEM:
// 1 query: SELECT * FROM customers
// N queries: SELECT * FROM orders WHERE customer_id=1 ... customer_id=N
List<Customer> customers = session.createQuery("FROM Customer", Customer.class).getResultList();
for (Customer c : customers) {
    c.getOrders().size();  // triggers N extra queries!
}

// SOLUTION 1: JOIN FETCH
List<Customer> customers = session
    .createQuery("FROM Customer c JOIN FETCH c.orders", Customer.class)
    .getResultList();  // 1 query with JOIN

// SOLUTION 2: @BatchSize
@OneToMany(mappedBy="customer")
@BatchSize(size=25)  // loads 25 collections in one IN query
private List<Order> orders;

// SOLUTION 3: EntityGraph
EntityGraph<Customer> graph = session.createEntityGraph(Customer.class);
graph.addAttributeNode("orders");
List<Customer> list = session.createSelectionQuery("FROM Customer", Customer.class)
    .applyFetchGraph(graph).getResultList();