JPA Specification multiple join based on foreignkey

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I have following relationships between three objects

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;
}

And this is actual database design enter image description here

Then, I'd like to make a specification to query as followings:

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

I am also using annotation for the specification which means that I use ProductEntity_, ProductInfoEntity_ and so on.

Can you please give me a full working code for the specification for query mentioned above?

Thank you guys

spring-data-jpa spring-mvc specifications jpa mysql
2 Answers

To use Specification your ProductInfoEntityRepository have to extend JpaSpecificationExecutor 

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

As far as I understand you use JPA metamodel. So then

@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);
    });
}

If you want to make specifications reusable you should create utility class contains two static methods productIdEquals(int) and languageIdEquals(int).

To combine them use Specifications(Spring Data JPA 1.*) or Specification(since Spring Data JPA 2.0)

user_102055140 
select * from product_info where product_id = 1 and support_language_id = 2;

Should work as written. But the only thing useful will be comment.

Perhaps you want the rest of the info in all three tables?

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.

From there, see if you can work out the obfuscation provided by JPA.

user_17668310
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