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Spring Boot

Cascade

  • Types: PERSIST saves children; MERGE updates; REMOVE deletes; REFRESH reloads; DETACH drops from context; ALL includes all.
  • orphanRemoval = true auto-deletes children removed from a parent collection.
@OneToMany(mappedBy = "order", cascade = CascadeType.ALL, orphanRemoval = true)
private List<OrderItem> items = new ArrayList<>();
  • Parent owns the child lifecycle = children are created/updated/deleted through the parent and should not outlive it; skip cascade for shared/many-to-many.
  • Keep cascading inside a single service-layer transaction.

Fetch

  • Fetch types: LAZY loads when accessed; EAGER loads immediately. Default is EAGER for @ManyToOne/@OneToOne, LAZY for @OneToMany/@ManyToMany.
  • Prefer explicit fetch = FetchType.LAZY on associations and load what you need with fetch joins or @EntityGraph.
@ManyToOne(fetch = FetchType.LAZY)
private Customer customer;

@Query("select o from Order o join fetch o.customer where o.id = :id")
Optional<Order> findWithCustomer(@Param("id") Long id);
  • Avoid EAGER on collections; it can explode queries and cause N+1 issues.