旧数据在OneToMany映射中被删除

Question

Product and ProductLine. One ProductLine can have many products.

Product.java:-

@Entity
    @Table(name ="PRODUCT")
    public class Product {
        @Id
        @GeneratedValue(strategy = GenerationType.AUTO)
        private int id;
        private String name;
    Product(String name){
            this.name=name;
        }
    }

ProductLine.java

   public class ProductLine {
        @Id
        @GeneratedValue(strategy = GenerationType.AUTO)
        private int id;
        @OneToMany(cascade = CascadeType.ALL)
        @JoinTable(name = "PRODUCTLINE_PRODUCT", joinColumns = @JoinColumn(name = "PRODUCTLINE_ID"), inverseJoinColumns = @JoinColumn(name = "PRODUCT_ID"))
        private List<Product> products=new ArrayList<>();

     public ProductLine(String name){
        this.name=name;
        }
    }

ProductLineRepository.java

 public interface ProductLineRepository extends JpaRepository<ProductLine,Integer> {
            ProductLine findOneById(String id);
        ProductLine findOneByName(String name);
        }

Controller:-

In the controller i have a am parsing the list of products associated with the Product from the user in the json form and persisting it into DB.

public void addData(){
        List<Product> products=new ArrayList<>();
        Product product1=new Product("Iphone");
        Product product2=new Product("Mac");
        products.add(product1);
        products.add(product2);
        ProductLine productLine=productLineRepository.findOneByName("Apple");
        productLine.setProducts(products);
        productLineRepository.save(productLine);
    }

Now if the Product Line "Apple" already exists then it deletes the entry in the Product Line table with the name "Apple" and then again inserts the data "IPhone" and "Mac" . But i do not want the old data to be deleted . What should i do?

Answer 1

This behavior is called orphanRemoval, when an entity is removed from the relation (this is what you are doing when setting new product list) it will be removed.

since JPA 2.0 the default value for orphanRemoval is false so if you are using this version or higher this behavior should not be there so i guess you are using lower version, either you use higher version or you can set the orphanRemoval attribute to false

@OneToMany(cascade = CascadeType.ALL, orphanRemoval="false")
@JoinTable(name = "PRODUCTLINE_PRODUCT", joinColumns = @JoinColumn(name = "PRODUCTLINE_ID"), inverseJoinColumns = @JoinColumn(name = "PRODUCT_ID"))
private List<Product> products=new ArrayList<>();

Answer 2

我可以通过使用findByName（）方法在持久性上下文中加载名称为“ Apple”的ProductLine来解决此问题，然后将与productLine关联的所有产品作为列表加载并将其添加到新创建的产品列表中。

Answer 3

Maybe I'm wrong...

but when you use this, seems like a @ManyToMany kind of mapping:

@OneToMany(cascade = CascadeType.ALL)
@JoinTable(name = "PRODUCTLINE_PRODUCT", joinColumns = @JoinColumn(name = "PRODUCTLINE_ID"), inverseJoinColumns = @JoinColumn(name = "PRODUCT_ID"))

If that's true, the natural behavior it's replace the old list to the new one... If you wanna a @OneToMany behavior you only need this:

@OneToMany(mappedBy = "product", cascade = CascadeType.ALL, fetch = FetchType.LAZY)