默认情况下，如果使用@ElementCollection标注一个实体中的子集合，这个集合是懒加载的，不会随着这个实体加载而立即加载：
@Entity
public class ShoppingCart implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
// LAZY is default懒加载默认
@ElementCollection(fetch = FetchType.LAZY)
private List<Product> products = new ArrayList<>();
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@Embeddable
public class Product implements Serializable {
private static final long serialVersionUID = 1L;
private String name;
private int price;
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当我们获取ShoppingCart这个实体时，其Product子集合是没有加载，只有访问这个集合时才会加载，但是如果需要这个子集合随着ShoppingCart加载，两个办法，去除懒加载策略；或者在Spring Boot的Repository中使用JOIN FETCH:
@Repository
public interface ShoppingCartRepository extends JpaRepository<ShoppingCart, Long> {
@Query(value = "SELECT p FROM ShoppingCart p JOIN FETCH p.products")
ShoppingCart fetchShoppingCart();
@Query(value = "SELECT p FROM ShoppingCart p JOIN FETCH p.products q WHERE q.price > ?1")
ShoppingCart fetchShoppingCartByPrice(int price);
}
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点击标题见Github源码