java - jpa实体映射情侣表

Question

我有用于 JSON 解析的实体

    @Entity
    public class Product{
    private int productId;
    private String productName;
    private BigDecimal productPrice;
    private int productVendorId;
    private String productVendorName;
    private int productCategoryId;
    private String productCategoryName;
    //getters setters here

在数据库中创建了 3 个表:产品(产品 ID、产品名称、产品价格、产品供应商 ID)、产品类别 ID)；供应商(供应商 ID，供应商名称)；类别(类别 ID，类别名称)；在第一个表中product_vendor_id fk->供应商中的vendor_id pk和类别中的product_category_id fk->category_id pk我尝试过这样的事情:

    @Entity
    @Table(name = "products, schema = "market")
    public class Product
    @Id
    @Column(updatable = false, nullable = false, name = "product_id")
    private int Id;
    @Column(name = "product_name")
    private String productName;
    @Column(name = "product_price")
    private BigDecimal productPrice;
    @Column(name = "product_vendor_id")
    private int productVendorId;
    @Columnt(table = "vendors", name = "vendor_name")
    private String vendor_name;
    @Column(name = "product_category_id")
    private int productCategoryId;
    @Column(table = "categories", name = "category_name")
    private String productCategorName;
    //getters setters here

收到很多错误:就像我在产品表中没有category_name列等。我在使用时收到此错误

     @Table(name = "products", schema = "market" )
     @SecondaryTables({@SecondaryTable(name = "vendors", schema = "market"),
     @SecondaryTable(name = "categories", schema = "market")})
     @JsonIgnoreProperties(ignoreUnknown = true)
     public class Product {
     ....
     @JoinColumn(name = "product_vendor_id", referencedColumnName = "vendor_id")
     private int productVendorID;
     @JoinColumn(table = "vendors", name = "vendor_name")
     private String productVendorName;
     @JoinColumn(name = "product_category_id", referencedColumnName = 
     "product_category_id")
     private int productCategoryID;
     @JoinColumn(table = "categories",  name = "category_name")
     private String productCategoryName;    

异常(exception):

     Caused by: org.postgresql.util.PSQLException: ERROR: column 
     product0_1_.product_id doesn't exist
     Hint: There may have been a link to the "product0_.product_id" column
     Position: 705     

我如何将该实体映射到 3 个表上？upd:我不想单独这个实体，我也需要它来反序列化我的 json 对象，只是想在不同的操作中重用这个实体。json示例

   {"productID":"1111111","productName":"Cool product","productPrice":"99.99","productVendorName":"Some store","productVendorID":"1337","productCategoryName":"Food","productCategoryID":"1"}

Answer 1

由于有 3 个单独的表，因此您需要创建三个单独的实体类。另外，我假设供应商和类别表与产品具有一对多的关系。尝试下面的代码:

产品:

@Entity
public class Product {
  @Id
  private int productId;
  private String productName;
  private BigDecimal productPrice;
  private String productVendorName;
  private String productCategoryName;
  @ManyToOne
  @JoinColumn(name = "productCategoryId")
  private Category category;
  @ManyToOne
  @JoinColumn(name = "productVendorId")
  private Vendors vendor;
}

类别:

@Entity
public class Category {
  @Id
  private Integer categoryId;
  private String categoryName;
  @OneToMany(mappedBy = "category", cascade = CascadeType.ALL, fetch = FetchType.LAZY, orphanRemoval = true)
  @NotEmpty
  private List<Product> products = new ArrayList<>();
}

供应商:

@Entity
public class Vendors {
  @Id
  private int vendorId;
  private String vendorName;
  @OneToMany(mappedBy = "vendor", cascade = CascadeType.ALL, fetch = FetchType.LAZY, orphanRemoval = true)
  @NotEmpty
  private List<Product> products = new ArrayList<>();
}

不过，我建议使用上述方法，如果您仍然想要单个实体类和 3 个包含冗余数据的单独表，请使用以下方法:

@Entity
@SecondaryTables({ @SecondaryTable(name = "vendors"), @SecondaryTable(name = "categories") })
public class Product {
  @Id
  private int productId;
  private String productName;
  private BigDecimal productPrice;
  private String productVendorName;
  private String productCategoryName;
  @Column(table = "categories")
  private Integer categoryId;
  @Column(table = "categories")
  private String categoryName;
  @Column(table = "vendors")
  private int vendorId;
  @Column(table = "vendors")
  private String vendorName;
}

主表的 id 列将出现在所有 3 个表中并用于连接它们。