JPA Entity States: New, Managed, Detached, Removed

Direct Answer

JPA describes new, managed, detached, and removed entity instances. A new entity has not been made persistent, even if application code has already assigned an id. A managed entity is tracked by a persistence context. A detached entity was managed but no longer is; its database row may still exist, may have changed, or may have been deleted. A removed entity is managed and scheduled for deletion.

Code Example

@Service
public class ProductService {
    private final ProductRepository repo;
    ProductService(ProductRepository r) { this.repo = r; }

    @Transactional
    public void lifecycle() {
        var product = new Product(null, "Laptop", 1200.0); // TRANSIENT
        repo.save(product);          // → MANAGED (id assigned)
        product.setPrice(1100.0);    // tracked, no save() needed
    }                                 // tx ends → product is DETACHED

    @Transactional
    public void delete(Long id) {
        var product = repo.findById(id).orElseThrow(); // MANAGED
        repo.delete(product);        // REMOVED — DELETE at commit
        System.out.println(product.getId()); // still readable in memory
    }
}

Common Mistakes & Pitfalls

• Detached ≠ removed — detached still exists in the DB; removed is scheduled for DELETE.
• Expecting dirty checking on detached entities — only managed entities auto-sync.
• Assuming save() on detached is a plain UPDATE — it's a merge (SELECT then UPDATE).
• delete() outside a transaction — the entity goes to removed but the DELETE never executes without a commit.