JPA Order by column in many to many relationship
<p>My problem is a bit more complex than described from the first sight. Let me try to explain.
I have two entities with unidirectional ManyToMany relationship:</p>

<pre><code>public class Category implements Serializable {

    @Id
    @Column(name = "ct_id")
    @SequenceGenerator(name = "category_ct_id_seq", sequenceName = "category_ct_id_seq", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "category_ct_id_seq")
    private Long id;

    @Column(name = "ct_name_key")
    private String nameKey;

    @ManyToMany
    @JoinTable(name = "category_2_country",
            joinColumns = @JoinColumn(name = "c2c_category_id"),
            inverseJoinColumns = @JoinColumn(name = "c2c_country_id"))
    private Set&lt;Country&gt; countries;
}

public class Country {

    @Id
    @SequenceGenerator(name = "country_c_id_seq", sequenceName = "country_c_id_seq", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "country_c_id_seq")
    @Column(name = "c_id")
    private Long id;

    @Column(name = "c_name")
    private String name;

    @Column(name = "c_iso_2_alpha")
    private String isoAlpha2Code;
</code></pre>

<p>And I'm retrieving the collection of Categories by an ISO code of country (actually, all categories, which has relation with the requested country). For this I've written a Specification:</p>

<pre><code>public class CategorySpecification implements Specification&lt;Category&gt; {

    Country matchCountry;

    @Override
    public Predicate toPredicate(Root&lt;Category&gt; root, CriteriaQuery&lt;?&gt; criteriaQuery, CriteriaBuilder builder) {

        return builder.isMember(matchCountry, root.get("countries"));

    }
}
</code></pre>

<p>This works pretty fine. The problem is I need to have order priority for the Categories in every Country.
The transitive table looks like this:
<a href="https://i.stack.imgur.com/a2ujc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/a2ujc.png" alt="enter image description here"></a>
So when I retrieve collection of Categories for the given Country, I want it to be ordered according to this <code>sort_order</code> column.</p>

<p>The corresponding SQL query looks so,thing like this:</p>

<pre><code>SELECT *
FROM category
  JOIN category_2_country ON category.ct_id = category_2_country.c2c_category_id
WHERE c2c_country_id = ?
ORDER BY sort_order;
</code></pre>

<p>But how should I make it in my JPA entities? And how should I persist it back to the database, it this order needs to be changed dynamically (e.g. from the admin panel)?</p>

<p>EDITED:
Tables in database corresponding to the entities:</p>

<p>The one for Country
<a href="https://i.stack.imgur.com/w5jXZ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/w5jXZ.png" alt="Country"></a></p>

<p>And the One for Category:
<a href="https://i.stack.imgur.com/yM1zp.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/yM1zp.png" alt="enter image description here"></a></p>

<p>EDITED 2:
I've managed to achieve the desired behaviour with a native query as follows:</p>

<pre><code>@Repository
public interface CategoryRepository extends JpaRepository&lt;Category, Long&gt;, JpaSpecificationExecutor&lt;Category&gt; {

    @Query(value = "SELECT ct.*\n" +
            "FROM category ct\n" +
            "  JOIN category_2_country c2c ON ct.ct_id = c2c.c2c_category_id\n" +
            "  JOIN country c ON c2c.c2c_country_id = c.c_id\n" +
            "WHERE c.c_iso_2_alpha = :countryIso\n" +
            "ORDER BY c2c.sort_order", nativeQuery = true)
    List&lt;Category&gt; findCategoriesForCountryOrdered(@Param("countryIso") String countryIso);
}
</code></pre>

<p>But still hope to have a more JPA/Hibernate way of doing this thing</p>