java - 如何创建多对多实体的命名查询？

Question

品牌

public class Brand implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "BrandID", nullable = false)
    private Integer brandID;
    @Basic(optional = false)
    @Column(name = "BrandName", nullable = false, length = 100)
    private String brandName;
    @Basic(optional = false)
    @Column(name = "Description", nullable = false, length = 1000)
    private String description;
    @Column(name = "Is_Visible")
    private Boolean isVisible;
    @JoinTable(name = "brandcategory", joinColumns = {
        @JoinColumn(name = "BrandID", referencedColumnName = "BrandID")}, inverseJoinColumns = {
        @JoinColumn(name = "CategoryID", referencedColumnName = "CategoryID")})
    @ManyToMany(fetch = FetchType.EAGER)
    private Collection<Category> categoryCollection;
    @OneToMany(mappedBy = "brand", fetch = FetchType.EAGER)
    private Collection<Product> productCollection;

我想从表 brandcategory whoes categoryID = :categoryID 中检索品牌 ID我如何在实体品牌中为其创建命名查询？

这不起作用:

@NamedQuery(name = "Brand.getBrandListByCategory",
            query = "SELECT b FROM Brand b WHERE b.brandID =
            (SELECT bc.brandID
             FROM b.brandctegory bc
             WHERE bc.category.categoryID = :categoryID)")

Answer 1

如果我没理解错的话，你想要属于一个类别的所有品牌。你为什么不简单地使关联双向。然后你可以这样做:

Category category = em.find(Category.class, categoryId);
return category.getBrands();

如果它是单向的，那么您将需要一个查询，但它比您尝试的查询简单得多:

select b from Brand b inner join b.categoryCollection category 
where category.id = :categoryId;

您的查询没有意义:它使用了一个不存在的关联 (b.brandcategory)。请记住，JPQL 使用实体、它们的持久字段以及与其他实体的关联。没有别的。 JPQL 中不存在表。