java - Spring Boot - 具有额外列的多对多关系的分页

Question

在使用带有额外列的多对多关系时，我找不到一种干净简单的方法来进行分页。

我的模型看起来像这样:

我有一个用户和一个产品模型。每个用户可以消费n个产品。每次消费都将存储在一个额外的表中，因为我想存储额外的信息，例如日期等。我已经实现了如下模型并且它有效，但我希望将用户的消费作为可分页的而不是检索整个集合。实现这一目标的最佳方法是什么？

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @OneToMany(
            mappedBy = "user",
            cascade = CascadeType.ALL,
            orphanRemoval = true
    )
    private List<Consumption> consumptionList = new ArrayList<>(); // never set this attribute

    public List<Consumption> getConsumptionList() {
        return consumptionList;
    }


    public void addConsumption(Product product) {
        Consumption consumption = new Consumption(this, product);
        consumptionList.add(consumption);
        product.getConsumptionList().add(consumption);
    }

    public void removeConsumption(Consumption consumption) {
        consumption.getProduct().getConsumptionList().remove(consumption);
        consumptionList.remove(consumption);
        consumption.setUser(null);
        consumption.setProduct(null);
    }
}

--

@Entity
@NaturalIdCache
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Product {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @OneToMany(
            mappedBy = "product",
            cascade = CascadeType.ALL,
            orphanRemoval = true
    )
    private List<Consumption> consumptionList = new ArrayList<>();

    public List<Consumption> getConsumptionList() {
        return consumptionList;
    }
}

这是我存储消耗的类。

@Entity
public class Consumption {

    @EmbeddedId
    private UserProductId id;

    @ManyToOne(fetch = FetchType.LAZY)
    @MapsId("userId")
    private User user;

    @ManyToOne(fetch = FetchType.LAZY)
    @MapsId("productId")
    private Product product;

    public Consumption(User user, Product product) {
        this.user = user;
        this.product = product;
        this.id = new UserProductId(user.getId(), product.getId());
    }

}

这是我的复合主键。

@Embeddable
public class UserProductId implements Serializable {

    @Column(name = "user_id")
    private Long userId;

    @Column(name = "product_id")
    private Long productId;

    private UserProductId() {
    }

    public UserProductId(Long userId, Long productId) {
        this.userId = userId;
        this.productId = productId;
    }

}

我希望能够调用诸如“getConclusionList(Page page)”之类的方法，该方法然后返回可分页。

希望你能帮助我!

提前谢谢您!

Answer 1

好吧，如果使用 Spring Boot，您可以使用存储库:

@Repository
public interface ConsumptionRepo extends JpaRepository<Consumption, Long>{
    List<Consumption> findByUser(User user, Pageable pageable);
}

然后你可以简单地调用它

ConsumptionRepo.findByUser(user, PageRequest.of(page, size);