使用休眠的外键连接

Question

大家好，我在使用休眠连接时遇到了一些错误 我使用 postgresql 9.5。

我的数据库表：cart (cart_id - primary key, cart.product_id references product.product_id - foreign key) 和 product (product_id - primary key)

Java 类 Cart 和 Product

@Entity
@Table(name = "product")
public class Product{
    @Id
    @Column(name = "product_id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int productId;

    @Column(name = "article")
    private String article;

    @Column(name = "name")
    private String name;

    @Column(name = "price")
    private BigDecimal price;

    @Column(name = "description")
    private String description;

    @Column(name = "manufacturer")
    private String manufacturer;

    @Column(name = "category")
    private String category;

    @Column(name = "unitsinstock")
    private long unitsInStock;

    @OneToOne(fetch = FetchType.LAZY)
    @PrimaryKeyJoinColumn
    private Cart cart;

和

    @Entity
    @Table(name = "cart")
    public class Cart {
    @Id
    @Column(name = "cart_id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int cartId;

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

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

    @Column(name = "quantity")
    private int quantity;

    @OneToOne(fetch = FetchType.LAZY, mappedBy = "cart", cascade = CascadeType.ALL)
    private Product product;

我应该如何注释我的类以便查询SELECT * FROM cart AS c INNER JOIN product p ON c.product_id = p.product_id？

我尝试使用名称/referencedColumnName 注释 @PrimaryKeyJoinColumn 和 @JoinColumn，但出现错误或 hibernate 进行查询（大部分），如SELECT * FROM cart AS c INNER JOIN product p ON c.cart_id = p.product_id 所以它“连接 cart_id 和 product_id，当我需要购物车和产品表中的 product_id 和 product_id 时。

更新。它之前工作正常，但在转储/恢复数据库后出现此错误。

我的 HQL 查询是 SELECT c FROM Cart c JOIN c.product

Answer 1

首先，惰性获取不适用于@OneToOne。观看this

---

你在 Cart 表上有外键，所以你应该像这样映射它：

购物车实体：

@OneToOne(cascade = CascadeType.All)
@JoinColumn(name = "product_id")
    private Product product;

对于产品实体：

@OneToOne(mappedBy = "product")
    private Cart cart;

如果我帮助了你，请投票作为答案）