Question

我是JPA和Spring的初学者。这也是我的第一个问题。所以，为我的错误感到抱歉。我正在从简单的场景开始练习。我有两个实体，分别是“产品”和“类别”，具有双向多对一/一对多关联。

类别：

@Entity
@Table(name = "categories")
@NoArgsConstructor
@AllArgsConstructor
@Data
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id", scope = Long.class)

public class Category implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @Column(name = "name", length = 50, nullable = false)
    private String name;

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "category")
    private List<Product> products = new ArrayList<Product>();
}

产品类别：

@Table(name = "products")
@NoArgsConstructor
@AllArgsConstructor
@Data
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id", scope = Long.class)

public class Product implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @Column(name = "title", nullable = false, length = 50)
    private String title;

    @Column(name = "price", precision = 4, scale = 2, nullable = false)
    private Double price;

    @Column(name = "quantity", nullable = false)
    private int quantity;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "category_id", foreignKey = @ForeignKey(name = "FK_product_category"))
    private Category category;
}

CategoryRepository和ProductRepository均从JpaRepository实现。带有@Query注释的方法签名很少。

使用带有@Autowired的存储库的服务。没有任何业务逻辑。

CategoryService类：

@Transactional
public class CategoryService implements IRepositoryService<Category, Long> {

    private ICategoryRepository categoryRepository;

    @Autowired
    public CategoryService(ICategoryRepository categoryRepository) {
        this.categoryRepository = categoryRepository;
    }

    @Override
    public List<Category> findAllOrderById() {
        return categoryRepository.findAllOrderById();
    }

    @Override
    public Category findById(Long id) {
        return categoryRepository.findById(id).orElseThrow(EntityNotFoundException::new);
    }

    @Override
    public List<Category> findByForeignKey(Long categoryId) {
        return null;
    }

    @Override
    public void add(Category category) {
        category.getProducts().forEach(product -> product.setCategory(category));
        categoryRepository.save(category);
    }

    @Override
    public void update(Category category) {
        categoryRepository.save(category);
    }

    @Override
    public void deleteById(Long id) {
        categoryRepository.deleteById(id);
    }

ProductService类：

@Transactional
public class ProductService implements IRepositoryService<Product, Long>{

    @Autowired
    private IProductRepository productRepository;

    @Override
    public List<Product> findAllOrderById() {
        return productRepository.findAllOrderById();
    }

    @Override
    public Product findById(Long id) {
        return productRepository.findById(id).orElseThrow(EntityNotFoundException::new);
    }

    @Override
    public List<Product> findByForeignKey(Long categoryId) {
        return productRepository.findByCategoryId(categoryId);
    }

    @Override
    public void add(Product entity) {
        productRepository.save(entity);
    }

    @Override
    public void update(Product entity) {
        productRepository.save(entity);
    }

    @Override
    public void deleteById(Long id) {
        productRepository.deleteById(id);
    }
}

最后，两个实体都有单独的restcontroller类。我在Postman中添加了一个仅带有名称的类别，因此product为空（这部分是正常的）。但是，当我从Postman或其他前端应用程序添加产品时，未设置产品的类别（我在json中设置category_id）。但是在数据库中，产品表的category_id列值为null。 json string

我也有延迟获取类型和json问题的问题。但是主要问题首先出现。

谢谢您的帮助。

Answer 1

只要您传递正确的json请求主体，上述JPA实体映射就应该起作用。另外，您可能需要使用@ JsonBackReference / @ JsonManagedReference以避免stackoverflow异常（有关更多信息，请参见JsonManagedReference vs JsonBackReference）

请求： POST：本地主机：/ cat

{ "name" :"Construction" }

POST：localhost：/ prod，这里我们使用类别ID =1。更改它以匹配“ Construction”类别的ID

{
"title" :"Bricks",
"price" :"1.2",
"quantity": "100",
"category": {
        "id": 1 
    }
}

将此类添加到jpademo包中并运行。

package jpademo;

import com.fasterxml.jackson.annotation.*;
import lombok.*;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.web.bind.annotation.*;

import javax.persistence.*;
import java.util.*;

@SpringBootApplication
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

@RestController
@RequiredArgsConstructor
class Ctrl {

    final CategoryRepo categoryRepo;
    final ProductRepo prodRepo;

    @PostMapping("/cat")
    void cat(@RequestBody Category cat) {
        categoryRepo.save(cat);
    }

    @PostMapping("/prod")
    void prod(@RequestBody Product p) {
        prodRepo.save(p);
    }

    @GetMapping("/cat")
    List<Category> cats() {
        return categoryRepo.findAll();
    }

    @GetMapping("/prod")
    List<Product> prods() {
        return prodRepo.findAll();
    }

}

interface CategoryRepo extends JpaRepository<Category, Long> {}

interface ProductRepo extends JpaRepository<Product, Long> {}

@Entity
@NoArgsConstructor
@AllArgsConstructor
@Data
class Category {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "category")
    @JsonManagedReference //to avoid Stackoverflow
    private List<Product> products = new ArrayList<>();
}

@Entity
@NoArgsConstructor
@AllArgsConstructor
@Data
class Product {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String title;

    private Double price;

    private int quantity;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "category_id", foreignKey = @ForeignKey(name = "FK_product_category"))
    @JsonBackReference
    private Category category;
}

Answer 2

这是使用杰克逊数据类型模块的唯一配置。

@Configuration
public class JacksonConfig {

    @Bean
    public Hibernate5Module hibernate5Module() {
        return new Hibernate5Module();
    }

    @Bean
    public AfterburnerModule afterburnerModule() {
        return new AfterburnerModule();
    }
}

这样的响应： json response

Spring：嵌套实体保存空值问题

2 个答案: