Spring Data JPA: Issues with FetchType.LAZY and Entity Relationships
Could someone explain I'm experimenting with I'm attempting to set up I'm working on a personal project and I'm experiencing an unexpected behavior when using `FetchType.LAZY` with my JPA entities in a Spring Boot application..... I have two entities, `Order` and `Customer`, where each `Order` is associated with one `Customer`. Here are the relevant parts of my code: ```java @Entity public class Order { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "customer_id") private Customer customer; // getters and setters } @Entity public class Customer { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; private String name; // getters and setters } ``` When I retrieve an `Order` from the database using a repository, I notice that the `Customer` field is not being loaded as expected. Here's how I'm fetching the data: ```java public List<Order> getAllOrders() { return orderRepository.findAll(); } ``` However, when I try to access the `Customer` of an `Order` in my service: ```java for (Order order : orders) { System.out.println(order.getCustomer().getName()); } ``` I get a `LazyInitializationException` saying: "failed to lazily initialize a collection of role: com.example.Order.customer, no session or session was closed". I understand that this is happening because the `EntityManager` is closed by the time I'm trying to access the `Customer`. I've tried various methods, including using `@Transactional` on my service method, but I still encounter the same issue. For example: ```java @Transactional public List<Order> getAllOrders() { List<Order> orders = orderRepository.findAll(); for (Order order : orders) { System.out.println(order.getCustomer().getName()); } return orders; } ``` However, the exception persists. Is there a better way to handle this fetching strategy, or should I consider using `FetchType.EAGER` instead? Are there any best practices for handling lazy loading in Spring Data JPA that I might be missing? I'm using Spring Boot 2.5.4 and Hibernate 5.5.7 here. Any ideas what could be causing this? Any examples would be super helpful. I'm working with Java in a Docker container on Windows 11. I'd be grateful for any help. Any help would be greatly appreciated!