SpringDataJPA @ManyToMany crud

Question

I want to insert a goods

with or without some categories already in database.

I have seen many similar problems and solution,seem like CascadeType ?

Actually I don't figure out.

here are two class and test

@Entity
@Table(name = "t_goods")
@Data
public class Goods implements Serializable {
    private static final long serialVersionUID = -7781710173608724249L;
    @Id
    @GenericGenerator(name = "goodsid",strategy = "uuid")
    @GeneratedValue(generator = "goodsid")
    private String goodsId;

    private String goodsName;

    @ManyToMany(cascade = {CascadeType.PERSIST})
    private Set<GoodsCate> goodsCateSet;
}

@Entity
@Table(name = "t_category",uniqueConstraints = { @UniqueConstraint(columnNames = "cateName")})
@Getter
@Setter
public class GoodsCate implements Serializable {
    private static final long serialVersionUID = -8990216455436375344L;
    @Id
    @GenericGenerator(name = "goodscateid",strategy = "uuid")
    @GeneratedValue(generator = "goodscateid")
    private String cateId;

    private String cateName;

   @ManyToMany(mappedBy = "goodsCateSet")
   private Set<Goods> goods;
}

@Test
void test(){

    Goods goods = new Goods();
    goods.setGoodsName("apple");

    GoodsCate food = new GoodsCate();
    food.setCateName("food");
    GoodsCate fooddb= goodsCateRepo.findGoodsCateByCateName(food.getCateName());
    if(fooddb!=null){
        food=fooddb;
    }
    GoodsCate vegetable= new GoodsCate();
    vegetable.setCateName("vegetable");
    GoodsCate vegetabledb = goodsCateRepo.findGoodsCateByCateName(vegetable.getCateName());
    if(vegetabledb!=null){
        vegetable = vegetabledb;
    }
    Set<GoodsCate> goodsCates = Sets.newSet(food, vegetable);


     goods.set(goodsCates);
     // goodsRepo is a interface extends jpaReposity
     goodsRepo.save(goods);

}

it throws

org.springframework.dao.InvalidDataAccessApiUsageException: detached entity passed to persist:com.xx.xxx.GoodsCate

Answer 1

It looks like you haven't linked your category to goods.

I would suggest to add two utility methods (eg addCategory(Category category) in Goods and addGood(Goods good) in Category) which are used to synchronize both sides of the bidirectional association. You should always provide these methods whenever you are working with a bidirectional association as, otherwise, you risk very subtle state propagation issues.

In Goods

public void addCategory(Category category) {
        categories.add(category);
        category.getGoods().add(this);
    }

In Category

public void addGood(Good good) {
        goods.add(good);
        good.getCategory().add(this);
    }

Note : Also don't forget to add remove utility just like above one.

Then you can use below code

@Test
    void test(){

        Goods goods = new Goods();
        goods.setGoodsName("apple");

        GoodsCate food = new GoodsCate();
        food.setCateName("food");
        GoodsCate fooddb= goodsCateRepo.findGoodsCateByCateName(food.getCateName());
        if(fooddb!=null){
            food=fooddb;
        }
        GoodsCate vegetable= new GoodsCate();
        vegetable.setCateName("vegetable");
        GoodsCate vegetabledb = goodsCateRepo.findGoodsCateByCateName(vegetable.getCateName());
        if(vegetabledb!=null){
            vegetable = vegetabledb;
        } 
        //********After adding mentioned utilites********    
         goods.addCategory(food);
         goods.addCategory(vegetable);
         // goodsRepo is a interface extends jpaReposity
         goodsRepo.save(goods);

    }

One of the article for Many to Many best practices