Spring MVC - loading data from database - spring

Question

I have two entities which are in many to many relation and I can't load Set <Category> categories. These fields are filled in the database.
#Entity
#Table(name="Product")
public class Product {
#Id
#GeneratedValue
private int idProduct;
private String status;
private String name;
#ManyToMany(fetch = FetchType.EAGER, mappedBy= "products")
private Set <Category> categories;
}
#Entity
#Table(name="Category")
public class Category {
#Id
#GeneratedValue
private int idCategory;
private String name;
#ManyToMany(fetch = FetchType.EAGER)
private Set <Product> products;
}
This returns nothing int the view and the loop doesn't rotate even once.
<c:forEach items="${product.categories}" var="items">
<p>${items.name}</p>
</c:forEach>
I join the schema. Could someone write what to do to make it work, please?
enter image description here
This not works.
#Entity
#Table(name="Category")
public class Category {
#Id
#GeneratedValue
private int idCategory;
private String name;
#ManyToMany(fetch = FetchType.EAGER)
#JoinTable(name = "Product_Category", joinColumns = {
#JoinColumn(name = "Category_idCategory", nullable = false, updatable = false) },
inverseJoinColumns = { #JoinColumn(name = "Product_idProduct",
nullable = false, updatable = false) })
private Set <Product> product;

Answer 1

Hibernate infers the sql that it needs to create from the annotation on the objects. Your product entity is telling hibernate to get information about the SQL join from the Category entity. This is from the mappedBy clause in the #ManyToMany annotation.
When it goes to the Category entity, it doesn't find what it needs, and it just gives an empty set.
Most #ManyToMany annotations are done with a join table. Here is a sample join table annotation
#JoinTable(name = "product_to_category", joinColumns = {
#JoinColumn(name = "category_id", nullable = false, updatable = false) },
inverseJoinColumns = { #JoinColumn(name = "product_id",
nullable = false, updatable = false) })
Depending on your schema, you might need to adjust the above annotation to get it working. It will give you a good start.