我可以将此Mysql查询转换为JPA吗？

Question

I'm fairly familiar with SQL but very new to the Java Persistence API. I'm using JPA through the Play Framework.

I have the following MySql query that I'd like to convert to pure JPA code if I can:

SELECT a.id, b.id
FROM Rankable a
INNER JOIN Rankable b on a.id < b.id
WHERE 
  a.category_id = ? AND b.category_id = ?
  AND NOT EXISTS (
    SELECT *
    FROM Comparison c
    WHERE c.lower in (a.id, b.id))
  AND NOT EXISTS (
    SELECT *
    FROM Comparison c
    WHERE c.higher IN (a.id, b.id))
ORDER BY a.id * rand()
LIMIT 1;

The purpose of this query is to select two rows from the Rankable table, but ensure that this specific pair is not present in the Comparison table.

What would be the best way to call a somewhat complicated query like this from Play/JPA?

Answer 1

It is possible to do a self join in JPA.

Take a look at this example

from the example

    @NamedQuery(name="siblings", query="select distinct sibling1 "
    + "from Deity sibling1, Deity sibling2 where "
    + "sibling1.father = sibling2.father "
    + "and sibling1.mother = sibling2.mother "
    + "and sibling2 = ?1 and sibling1 <> ?1"),