Spring Boot Entity how to check value if exist in another table by custom field - spring-boot

Question

The user can search for products if any product shown in the result exists in the user_favorites table so the show flag tells the front-end this product was added for this user by user_id and product_id. with spring boot and spring data.
My Entity :
#Id
#Column(name = "catId")
private Integer catId;
#Column(name = "cat_no")
private String catNo;
#Column(name = "cat_sn")
private String catSn;
#Column(name = "doc_ref")
private String docRef;
#Column(name = "user_id")
private Integer userId;
#Column(name = "updated_at")
private String updatedAt;
#Column(name = "created_at")
private String createdAt;
I tried that using #Formula but nothing happing always returns null. and if it's done by #Formula how can i add parameters to #Formula
#Formula(value = "SELECT count(*) as checker FROM fb_user_favorites WHERE cat_id = 34699 AND user_id = '52') ")
#Transient
private String checker;

Answer 1

#Transient is part of JPA spec. In Hibernate fields marked with this annotation just simply ignored/excluded from any JPA engine/runtime logic.
#Formula is part of Hibernate. Fields, marked with it, don't persisted by Hibernate (first argument do not use #Transient as redundant), values are calculated by provided SQL when executing query for entity.
So for Hibernate to see this fields, they should not be excluded by #Transient
TL;DR remove #Transient annotation

Answer 2

Complicated but fast working way.
Adding isFavorite field to the entity:
#Transient
private boolean isFavorite;
Create an entity linking Product and User:
public class ProductFavorite {
#Id
#GeneratedValue(strategy = IDENTITY)
private Long id;
#ManyToOne(optional = false, fetch = LAZY)
private Product product;
#ManyToOne(optional = false, fetch = LAZY)
private User user;
}
Then create a repository with a method to find the user's favorite products:
#Repository
public interface ProductLikeRepository extends JpaRepository<ProductFavorite, Long> {
#Query("select f.product.id from ProductFavorite f where f.product in ?1 and f.user = ?2")
Set<Integer> findProductIdsByIdsAndUser(List<Product> products, User user);
}
And at the end, write a method that will fill in the isFavorite field:
public void fillFavorite(List<Product> products, User user) {
if (products.isEmpty()) {
return;
}
var likedIds = favoriteRepository.findProductIdsByIdsAndUser(products, user);
for (Product product : products) {
product.setFavorite(likedIds.contains(product.getId()));
}
}
You need to call it manually:
List<Product> products = productRepository.findAll();
fillFavorite(products, currentUser());