Many to many Jpa Query Spring boot - mysql

Question

I have three mysql tables with a many to many relationship and I am trying to make a Jpa Query on spring boot. The tables are
product with fields id, name
extra with fields id, name
product_extra with fields id, product_id, extra_id
Product table has a many to many relationship with extra table, as a product can have many extras hence the need for product_extra table
Here is the query i would like to include in my project
SELECT extra.name
FROM extra
INNER JOIN product_extra ON extra_id = extra.id
WHERE product_id = ?;
Should i have like a #ManyToMany annotation and where should i have it

Answer 1

Yes you should. Use #ManyToMany to map between Product and Extra.Make sure to use Set instead of List for the mapping in order to have better performance. It looks like:
#Entity
#Table(name="product")
public class Product{
#ManyToMany(cascade = {CascadeType.PERSIST,CascadeType.MERGE})
#JoinTable(name = "product_extra",
joinColumns = #JoinColumn(name = "product_id"),
inverseJoinColumns = #JoinColumn(name = "extra_id")
)
private Set<Extra> extras = new HashSet<>();
}
#Entity
#Table(name="extra")
public class Extra{
#ManyToMany(mappedBy = "extras")
private Set<Product> products = new HashSet<>();
}
After mapping them , you can then use JPQL to get a product by id together with its extra by :
select p from Product p left join fetch p.extras where p.id = :productId;