JPA双向关联：ManyToOne删除父级时如何删除关联？

问题描述

我有两个实体：Product 和 Category

  public class Category {
    @Id
    @GeneratedValue(generator = "inc")
    @GenericGenerator(name = "inc",strategy = "increment")
    private int id;

    @OnetoMany(cascade =  CascadeType.PERSIST,mappedBy = "category")
    private Set<Product> products;
}

public class Product {
    @Id
    @GeneratedValue(generator = "inc")
    @GenericGenerator(name = "inc",strategy = "increment")
    private int id;

    @ManyToOne
    @JoinColumn(name = "categories_id")
    private Category category;
}

我想在删除父级（类别）后将我的孩子（产品）保留在 db 中（category 的值等于 null）。 目前，当我尝试删除类别时，出现此错误：

org.h2.jdbc.JdbcsqlIntegrityConstraintViolationException: referential integrity constraint violation: "CONSTRAINT_F2: PUBLIC.PRODUCTS FOREIGN KEY(CATEGORIES_ID) REFERENCES PUBLIC.CATEGORIES(ID)

解决方法

在删除类别之前，您需要更新关联。 例如：

Category category = ...
for (Product p : category.getProducts()) {
   p.setCategory(null);
}
category.getProducts().clear();
entityManager.remove(category);