@Entity
public class Category implements NamedModel {
    @Id
    @Column(name = "CATEGORY_ID")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;

    @OneToOne(cascade = CascadeType.REMOVE, fetch = FetchType.EAGER)
    @JoinTable(name = "CATEGORY_RELATIONS",
            joinColumns = {
                    @JoinColumn(name = "CATEGORY_RELATIONS_CATEGORY_ID", referencedColumnName = "CATEGORY_ID")},
            inverseJoinColumns = {
                    @JoinColumn(name = "CATEGORY_RELATIONS_PARENT_ID", referencedColumnName = "CATEGORY_ID")})
    private Category parent;

    @OneToMany(cascade = CascadeType.REMOVE, fetch = FetchType.LAZY, mappedBy = "parent")
    private List<Category> children;

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Category)) return false;
        if (!super.equals(o)) return false;

        Category category = (Category) o;

        return !(image != null ? !image.equals(category.image) : category.image != null)
                && !(parent != null ? !parent.equals(category.parent) : category.parent != null)
                && !(children != null ? !children.equals(category.children)
                : category.children != null);

    }
}
//-----------------------------------------
@Entity
@SuppressWarnings("unused")
@Table(name = "CATEGORY_RELATIONS")
@IdClass(CategoryRelations.CategoryRelationsPrimaryKey.class)
public class CategoryRelations implements Serializable {

    @Id
    @Column(name = "CATEGORY_RELATIONS_CATEGORY_ID")
    private long categoryId;

    @Id
    @Column(name = "CATEGORY_RELATIONS_PARENT_ID")
    private long parentId;

    @Entity
    @IdClass(CategoryRelationsPrimaryKey.class)
    public static class CategoryRelationsPrimaryKey implements Serializable {
        private Long categoryId;
        private Long parentId;

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;

            CategoryRelationsPrimaryKey that = (CategoryRelationsPrimaryKey) o;

            return categoryId != null && categoryId.equals(that.categoryId)
                    && parentId != null && parentId.equals(that.parentId);
        }
        public int hashCode() {...}
    }
}

@OneToOne(fetch = FetchType.EAGER)
@JoinTable(name = "CATEGORY_RELATIONS",
    joinColumns = {
        @JoinColumn(name = "CATEGORY_RELATIONS_CATEGORY_ID", referencedColumnName = "CATEGORY_ID")},
    inverseJoinColumns = {
        @JoinColumn(name = "CATEGORY_RELATIONS_PARENT_ID", referencedColumnName = "CATEGORY_ID")})
private Category parent;