使用休眠的外键联接

Question

大家好，在使用休眠连接时我遇到了一些错误，我使用的是PostgreSQL 9.5。

我的数据库表： cart (cart_id - primary key, cart.product_id references product.product_id - foreign key) 购物车 (cart_id - primary key, cart.product_id references product.product_id - foreign key)和产品 (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班级以使查询SELECT * FROM cart AS c INNER JOIN product p ON c.product_id = p.product_id ？

我尝试了使用名称/ referencedColumnName的annotane @PrimaryKeyJoinColumn和@JoinColumn，但是遇到了错误或休眠状态的查询（主要是SELECT * FROM cart AS c INNER JOIN product p ON c.cart_id = p.product_id因此它“连接了cart_id和product_id，当我在购物车和产品表中需要product_id和product_id时。

更新。 之前运行良好，但是在转储/还原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，@ OneToOne无法使用懒惰获取。 看这个

---

您在Cart表上具有外键，因此应按以下方式映射它：

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;

如果我有帮助，请投票作为答案）