Can't create entity object with map with custom object - spring-boot

Question

Spring boot 2.5
I has entity Cart. One cart has many entities Product. In one cart has many products. So I try with #JoinColumn but I get error:
#Entity
public class Cart {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int id;
#OneToMany(mappedBy = "cart", fetch = FetchType.EAGER,
cascade = CascadeType.ALL)
private Map<Product, Integer> products;
}
import javax.persistence.*;
#Entity
public class Product {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int id;
#ManyToOne(fetch = FetchType.EAGER, optional = false)
#JoinColumn(name = "cart_id", nullable = false)
private Cart cart;
}
But when I try to run application I get error:
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mvcConversionService' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.format.support.FormattingConversionService]: Factory method 'mvcConversionService' threw exception; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'cartRepository' defined in com.myproject.eshop_orders.repo.CartRepository defined in #EnableJpaRepositories declared on JpaRepositoriesRegistrar.EnableJpaRepositoriesConfiguration: Cannot resolve reference to bean 'jpaMappingContext' while setting bean property 'mappingContext'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'jpaMappingContext': Invocation of init method failed; nested exception is org.hibernate.AnnotationException: Use of #OneToMany or #ManyToMany targeting an unmapped class: com.myproject.eshop_orders.api.model.Cart.products[java.lang.Integer]

Answer 1

If you want a map you need to use #MapKeyJoinColumn. Something like this
#Entity
public class Cart {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int id;
#MapKeyJoinColumn(name="PRODUCT_ID")
#OneToMany(mappedBy = "cart", fetch = FetchType.EAGER,
cascade = CascadeType.ALL)
private Map<Product, Integer> products;
}

Answer 2

One cart has many different products.
Also I need to store quantity of products in cart (value in map)
Here my solution:
#Entity
public class Cart {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int id;
#ElementCollection
#CollectionTable(name = "cart_products", joinColumns = #JoinColumn(name = "cart_id"))
#MapKeyJoinColumn(name = "product_id")
#Column(name = "product_qantity")
private Map<Product, Integer> products;
}
import javax.persistence.*;
#Entity
public class Product {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int id;
#ManyToOne(fetch = FetchType.EAGER, optional = false)
#JoinColumn(name = "cart_id", nullable = false)
private Cart cart;
}
Is this a correct solution?