How To Avoid LazyInitializationException Via JOIN FETCH
** See also:**
- LEFT JOIN FETCH
- JOIN FETCH And DTOs
- JOIN VS. JOIN FETCH
Description: Typically, when we get a LazyInitializationException we tend to modify the relationship fetching type from LAZY to EAGER. That is bad! This is a code smell. Best way to avoid this exception is to rely on JOIN FETCH and/or DTOs. JOIN FETCH allows associations or collections of values to be initialized along with their parent objects using a single SELECT. This application is a JOIN FETCH example with entities. But, with some constraints, JOIN FETCH can be used with DTOs as well. An example is available here.
Key points:
- define two related entities (e.g., Author and Book in a one-to-many lazy bidirectional relationship)
- write a JPQL JOIN FETCH to fetch an author including his books
- write a JPQL JOIN FETCH to fetch a book including its author
Output example:
