JPA Specification multiple join based on foreignkey - mysql

Question

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
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

Answer 1

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)

Answer 2

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.