多對一：JSON決議錯誤無法構造實體

我使用 Spring Boot 開發 REST API 我有兩個具有雙向 OneToMany 的物體

產品類別

public class Product {

    private Long productId;
    private String name;
    private String description;
    private List<ProductList> productList;


    public Product() {
    }


    public Product(Long productId, String name, String description, List<ProductList> productList) {
        this.productId = productId;
        this.name = name;
        this.description = description;
        this.productList = productList;
    }


    public Long getProductId() {
        return productId;
    }

    public void setProductId(Long productId) {
        this.productId = productId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public List<ProductList> getProductList() {
        return productList;
    }

    public void setProductList(List<ProductList> productList) {

        this.productList = productList;
    }

ProductList class

public class ProductList {

    private Long productListId;
    private String productListName;
    private Product product;


    public ProductList(Long productListId, String productListName, Product product) {
        this.productListId = productListId;
        this.productListName = productListName;
        this.product = product;
    }


    public ProductList() {
    }


    public Long getProductListId() {
        return productListId;
    }

    public void setProductListId(Long productListId) {
        this.productListId = productListId;
    }

    public String getProductListName() {
        return productListName;
    }

    public void setProductListName(String productListName) {
        this.productListName = productListName;
    }

    public Product getProduct() {
        return product;
    }

    public void setProduct(Product product) {
        this.product = product;
    }
}

ProductEntity class:

@Entity
@Data
@Table(name = "PRODUCT")

public class ProductEntity {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column
private Integer productId;

@Column
private String name;

@Column
private String description;

@OneToMany(cascade = CascadeType.ALL, mappedBy="product", fetch = 
FetchType.EAGER)
private List<ProductListEntity> productList;
// Getters,Setters,No-ArgCOnstructor, All-ArgConstructor

ProductListEntity class:

@Table
@Entity
@Data
public class ProductListEntity {


@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long productListId;
private String productListName;


@ManyToOne(fetch = FetchType.EAGER, targetEntity = ProductEntity.class)
@JoinColumn(name = "FK_Product", referencedColumnName = "productId")
private ProductEntity product;

Service to save data:

public void addProduct(Product product) {
    ProductEntity productEntity = new ProductEntity();
    BeanUtils.copyProperties(product, productEntity);
    productRepository.save(productEntity);
}

When i try to post I get this error:

"message": "JSON parse error: Cannot construct instance of eteosf.hexagonal.domain.model.Product (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('string'); nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of eteosf.hexagonal.domain.model.Product (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('string')\n at [Source: (PushbackInputStream); line: 9, column: 18] (through reference chain: eteosf.hexagonal.domain.model.Product["productList"]->java.util.ArrayList[0]->eteosf.hexagonal.domain.model.Product$ProductList["product"])", "path": "/product"

JSON request body:

{
  "productId": 0,
  "name": "string",
  "description": "string",
  "productList": [
    {
      "productListId": 0,
      "productListName": "string",
      "product": "string"
    }
  ]
}

uj5u.com熱心網友回復：

在您的 json_request 中，在 productList 中，您將“產品”作為“字串”發送。但是 Deserializer 不能將該字串轉換為 Product 物件。它必須作為 object 發送{}。您可以將該物件留空 - 如果它所做的只是指向自身，則不要發送它。

您基本上犯了混淆不同原則的錯誤-整個雙向關系僅適用于持久性級別。Json 請求是在控制器/視圖級別發送的，因此您不能以相同的方式顯示雙向性質。這就是您不使用物體作為控制器引數而是使用 DTO 的原因。

在您的情況下，請不要為控制器發送“產品”欄位：

{
  "productId": 0,
  "name": "string",
  "description": "string",
  "productList": [
    {
      "productListId": 0,
      "productListName": "string",
    }
  ]
}

并在收到引數后立即將其添加到控制器方法中：

//the receiving controller method which got Parameter `ProductEntity product`
product.getProductList().forEach(productList -> productList.setProduct(product);

就像我說的，你不應該在 Controller 方法中使用物體，它應該是一個 DTO 類以避免這種問題

標籤：mysql spring hibernate jpa

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