Spring Data JPA - Lazy loading and #Fetch( FetchMode.JOIN) - spring-boot

Question

2 Entity ProductMaster and Category
#Entity
#Table(name = "product_master")
#JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
#NamedQuery(name = "ProductMaster.findAll", query = "SELECT p FROM ProductMaster p")
public class ProductMaster implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String description;
//Many Product will have one categoary
#ManyToOne(fetch=FetchType.LAZY)
#JoinColumn(name="category_id")
private Category category;
//get and set fn
}
#Entity
#JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
#Table(name = "category")
public class Category {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(name = "category_name")
private String categoryName;
#JsonIgnore
#OneToMany(cascade = CascadeType.ALL, mappedBy = "category")
#Fetch( FetchMode.JOIN)
private Set<ProductMaster> products = new HashSet<ProductMaster>();
//get and set fn
}
while fetchAll in JPA repository of Product. Join is performed and its expected
Hibernate:
select
productmas0_.id as id1_1_,
productmas0_.category_id as categor11_1_,
productmas0_.created_by as created_2_1_,
productmas0_.created_dt as created_3_1_,
productmas0_.description as descript4_1_,
productmas0_.image as image5_1_,
productmas0_.is_favorite as is_favor6_1_,
productmas0_.price as price7_1_,
productmas0_.title as title8_1_,
productmas0_.updated_by as updated_9_1_,
productmas0_.updated_dt as updated10_1_
from
product_master productmas0_ limit ?
Hibernate:
select
category0_.id as id1_0_0_,
category0_.category_name as category2_0_0_,
category0_.created_by as created_3_0_0_,
category0_.created_dt as created_4_0_0_,
category0_.category_desc as category5_0_0_,
category0_.updated_by as updated_6_0_0_,
category0_.updated_dt as updated_7_0_0_,
products1_.category_id as categor11_1_1_,
products1_.id as id1_1_1_,
products1_.id as id1_1_2_,
products1_.category_id as categor11_1_2_,
products1_.created_by as created_2_1_2_,
products1_.created_dt as created_3_1_2_,
products1_.description as descript4_1_2_,
products1_.image as image5_1_2_,
products1_.is_favorite as is_favor6_1_2_,
products1_.price as price7_1_2_,
products1_.title as title8_1_2_,
products1_.updated_by as updated_9_1_2_,
products1_.updated_dt as updated10_1_2_
from
category category0_
left outer join
product_master products1_
on category0_.id=products1_.category_id
where
category0_.id=?
but while fetchAll in JPA repository of category multiple query for product are fired. I want lazy loading behavior here for product while fetch all in Category
select
category0_.id as id1_0_,
category0_.category_name as category2_0_,
category0_.created_by as created_3_0_,
category0_.created_dt as created_4_0_,
category0_.category_desc as category5_0_,
category0_.updated_by as updated_6_0_,
category0_.updated_dt as updated_7_0_
from
category category0_ Hibernate:
select
products0_.category_id as categor11_1_0_,
products0_.id as id1_1_0_,
products0_.id as id1_1_1_,
products0_.category_id as categor11_1_1_,
products0_.created_by as created_2_1_1_,
products0_.created_dt as created_3_1_1_,
products0_.description as descript4_1_1_,
products0_.image as image5_1_1_,
products0_.is_favorite as is_favor6_1_1_,
products0_.price as price7_1_1_,
products0_.title as title8_1_1_,
products0_.updated_by as updated_9_1_1_,
products0_.updated_dt as updated10_1_1_
from
product_master products0_
where
products0_.category_id=? 2022-09-25 13:39:56.507 TRACE 14160 --- [nio-8080-exec-5] o.h.type.descriptor.sql.BasicBinder : binding parameter [1] as [BIGINT] - [2] Hibernate:
select
products0_.category_id as categor11_1_0_,
products0_.id as id1_1_0_,
products0_.id as id1_1_1_,
products0_.category_id as categor11_1_1_,
products0_.created_by as created_2_1_1_,
products0_.created_dt as created_3_1_1_,
products0_.description as descript4_1_1_,
products0_.image as image5_1_1_,
products0_.is_favorite as is_favor6_1_1_,
products0_.price as price7_1_1_,
products0_.title as title8_1_1_,
products0_.updated_by as updated_9_1_1_,
products0_.updated_dt as updated10_1_1_
from
product_master products0_
where
products0_.category_id=?
Problem statement to resolved here is that Number of Product query will be number of row in category table. We want this to be lazy load and don't want to perform multiple query for product while selecting category.

Answer 1

If you want a single query you should use left join fetch :
select c from Category c left join fetch c.products
And for the problem of multiple categories read this article
https://vladmihalcea.com/jpql-distinct-jpa-hibernate/

Answer 2

OneToMany relationships are inherently lazy but setting Fetch( FetchMode.JOIN) will override this lazy behaviour so should be removed if you want lazy fetching of products