java - Hibernate 查找错误的主键

Question

我的实体有两个外键，其中之一是主键。我在JPA Wiki中读到如果子级(采购)主键与父级(商品)主键相同，则建立 @OneToOne 关系。

@SuppressWarnings("serial")
@Entity
public class Procurement implements Serializable {

    @Id
    @OneToOne
    // the child's primary key is the same as the parent
    @JoinColumn(name = "articleId", referencedColumnName = "id")
    private Article article;

    @OneToOne
    @JoinColumn(name = "supplierId", referencedColumnName = "id")
    private Supplier supplier;

按照标准方法，JpaRepository 应如下所示:

@Repository
public interface IProcurementRepository extends
        JpaRepository<Procurement, Article>

但是，如果我想调用 findOne 方法(查找主键)来传递“Article”对象，Hibernate 会抛出异常。

org.hibernate.TypeMismatchException: Provided id of the wrong type for class de.willms.spring.myerp.model.Procurement. Expected: class de.willms.spring.myerp.model.Procurement, got class de.willms.spring.myerp.model.Article

数据库表结构:

表“文章”(ID、短文本)

表“供应商”(ID、名称)

表“采购”(文章ID、供应商ID、价格)

我需要更改什么才能通过相应的“文章”对象找到“采购”记录？

Answer 1

最后，我在 Hibernate 中发现了一个特殊的函数(令人惊奇，但在文档中很难理解)，从而找到了解决方案。

一旦主键由多个列组成，或者像我的例子一样，与其他表相关，就必须编写一个特殊的 ID 类。

@Embeddable    
public class Procurement_ID implements Serializable {

    /**
     * This attribute establishes the 1:1 connection to a record in the
     * "article" table. The column "articleId" is a foreign key to the column
     * "id" in the {@link Article} entity. (Warning: This is Hibernate
     * specific!)
     */
    @OneToOne
    @JoinColumn(name = "articleId", referencedColumnName = "id")
    private Article article;

    /**
     * This attribute establishes the 1:1 connection to a record in the table
     * "supplier". The column "supplierId" is a foreign key to the column "id"
     * in the {@link Supplier} entity. (Warning: This is Hibernate specific!)
     */
    @OneToOne
    @JoinColumn(name = "supplierId", referencedColumnName = "id")
    private Supplier supplier;

(由于更加“规范化”的数据模型，我切换到复合主键。)

由于@Embeddable注解的存在，这个ID可以注入(inject)到实体类中。

@Entity
public class Procurement implements Serializable {

    /**
     * The composite primary key of the underlying table is defined in the
     * {@link Procurement_ID} class.
     */
    @EmbeddedId
    private Procurement_ID procid;

当我使用这种方法时，Hibernate 会插入一 strip 有正外键检查的新记录:

[DEBUG] Generated identifier: component[article,supplier]{article=de.willms.spring.myerp.model.Article#1, supplier=de.willms.spring.myerp.model.Supplier#1}, using strategy: org.hibernate.id.CompositeNestedGeneratedValueGenerator

... (Flusing) ...

[DEBUG] Listing entities: ... de.willms.spring.myerp.model.Procurement{price=2.5, deliveryTime=10, procid=component[article,supplier]{article=de.willms.spring.myerp.model.Article#1, supplier=de.willms.spring.myerp.model.Supplier#1}, priceUnit=$}

然而，遗憾的是，JpaRepository 无法注入(inject)仅涉及主键一部分的 find() 方法 stub 。它“无法根据路径解析属性”。欢迎大家留言评论!