JPA规范基于外键的多重连接

Question

我在三个对象之间有以下关系

public class ProductEntity {
    @Id
    private int id;

    @OneToMany(mappedBy = "productEntity",
               fetch = FetchType.LAZY)
    private List<ProductInfoEntity> productInfoEntityList = new ArrayList<>();

    @Column(name = "snippet")
    private String snippet;
}

public class ProductInfoEntity {
    @Id
    private int id;

    @ManyToOne
    @JoinColumn(name = "product_id")
    private ProductEntity productEntity;

    @ManyToOne
    @JoinColumn(name = "support_language_id")
    private SupportLanguageEntity supportLanguageEntity;
}


public class SupportLanguageEntity {
    @Id
    private int id;

    @Column("name")
    private String name;
}

这是实际的数据库设计

那么，我想做一个规范查询如下：

select * 来自 product_info 其中 product_id = 1 support_language_id = 2;

我还在规范中使用注释，这意味着我使用 ProductEntity_、ProductInfoEntity_ 等等。

能否提供上述查询规范的完整工作代码？

谢谢大家

Answer 1

select * from product_info where product_id = 1 and support_language_id = 2;

应该如书面那样工作。但唯一有用的是 comment.

也许您需要所有三个表格中的其余信息？

SELECT  pi.comment,   -- list the columns you need
        p.snippet,
        sl.name
    FROM product AS p      -- table, plus convenient "alias"
    JOIN product_info AS pi  -- another table
        ON p.id = pi.product_info  -- explain how the tables are related
    JOIN support_language AS sl  -- and another
        ON pi.support_language_id = sl.id  -- how related
    WHERE  p.snippet = 'abc'   -- it is more likely that you will start here
    -- The query will figure out the rest.

从那里开始，看看您是否可以解决 JPA 提供的混淆问题。

Answer 2

使用Specification your ProductInfoEntityRepository have to extend JpaSpecificationExecutor

@Repository
public interface ProductInfoEntityRepository 
    extends JpaRepository<ProductInfoEntity, Integer>, JpaSpecificationExecutor<ProductInfoEntity> {
}

据我了解，您使用 JPA 元模型。那么

@Autowired    
ProductInfoEntityRepository repository;

public List<ProductInfoEntity> findProductInfoEntities(int productId, int languageId) {
    return repository.findAll((root, query, builder) -> {
        Predicate productPredicate = builder.equal(
                root.get(ProductInfoEntity_.productEntity).get(ProductEntity_.id), // or root.get("productEntity").get("id")
                productId); 

        Predicate languagePredicate = builder.equal(
                root.get(ProductInfoEntity_.supportLanguageEntity).get(SupportLanguageEntity_.id),  // or root.get("supportLanguageEntity").get("id")
                languageId);

        return builder.and(productPredicate, languagePredicate);
    });
}

如果你想让规范可重用，你应该创建实用程序 class 包含两个静态方法 productIdEquals(int) 和 languageIdEquals(int)。

要组合它们，请使用 Specifications(Spring Data JPA 1.*) or Specification（因为 Spring Data JPA 2.0）

JPA规范基于外键的多重连接

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