what is the meaning of hibernate inverseJoinColumns?

Question

I understand hibernate @JoinTable annotation, but I don't understand the inverseJoinColumns. What is it used for?

e.g.

 @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
 @JoinTable(name = "stock_category", catalog = "mkyongdb", joinColumns = {
        @JoinColumn(name = "STOCK_ID", nullable = false, updatable = false) },
        inverseJoinColumns = { @JoinColumn(name = "CATEGORY_ID",
                nullable = false, updatable = false) })

 public Set<Category> getCategories() {
    return this.categories;
}

Answer 1

From the javadocs, it means:

(Optional) The foreign key columns of the join table which reference the primary table of the entity that does not own the association

In layman's terms, it is the column of Category that will be used as a part of the JoinTable relationship between the current entity and Category.

If you don't specify joinColumns and inverseJoinColumns on the @JoinTable annotation, the persistence provider assumes a primary key to primary key join relationship and still store the equivalent ID columns for two related entities in the table by default.

Answer 2

For example, we have 2 models: User and Role. The relationship between those 2 models will be Many-to-Many. User Model:

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(name = "user_roles", joinColumns = @JoinColumn(name = "user_id"), inverseJoinColumns = @JoinColumn(name = "role_id"))
private Set<Role> roles = new HashSet<>();

Role Model:

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;

@Enumerated(EnumType.STRING)
@Column(length = 20)
private ERole name;

The joinColumn attribute will connect to the owner side of the relationship, and the inverseJoinColumn to the other side