Java Spring boot，@ManyToMany，为联接表创建一个存储库

我有两个实体，它们之间有很多关系：

@Entity
@Table(name="categories")
public class CategoryEntity implements Serializable{

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="id")
    private int categoryId;

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


    @ManyToMany(mappedBy = "categories")
    private List<ProductEntity> products = new ArrayList<ProductEntity>();
}

@Entity
@Table(name="products")
public class ProductEntity implements Serializable{

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="id")
    private Integer productId;

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

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

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

    @Column(name="rating")
    private Float rating;

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

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

    @ManyToMany(cascade = {
            CascadeType.PERSIST,
            CascadeType.MERGE
    })
    @JoinTable(name = "product_category",
        joinColumns = {@JoinColumn(name = "product_id")},
        inverseJoinColumns = {@JoinColumn(name = "category_id")}
    )
    private List<CategoryEntity> categories = new ArrayList<>();
}

---

你有关系一致性问题。您正在将类别添加到产品中，但未将产品添加到类别中

将此方法添加到ProductEntity类中：

 public void addCategory(CategoryEntity category) {
        this.getCategories().add(category);
        category.getProducts().add(this);
    }

并使用此方法将类别添加到产品中

ProductEntity productEntity=productMapper.dtoToEntity(productDto);
for(CategoryDto categoryDto:productDto.getCategories()){
    CategoryEntity categoryEntity=categoryMapper.dtoToEntity(categoryDto);
    productEntity.addCategory(categoryEntity); //changed line
   }
productEntity=productService.saveProduct(productEntity);
productDto.setProductId(productEntity.getProductId());

 public void addCategory(CategoryEntity category) {
        this.getCategories().add(category);
        category.getProducts().add(this);
    }

ProductEntity productEntity=productMapper.dtoToEntity(productDto);
for(CategoryDto categoryDto:productDto.getCategories()){
    CategoryEntity categoryEntity=categoryMapper.dtoToEntity(categoryDto);
    productEntity.addCategory(categoryEntity); //changed line
   }
productEntity=productService.saveProduct(productEntity);
productDto.setProductId(productEntity.getProductId());