How to make a JPA query with LEFT OUTER JOIN

问题

Based on these two tables (and their corresponding entities) :

profiles(id, email, name)
items(id, profile_id, rank, price)

Profile(email, name)
Item(profile, rank, price)

I have to list all the profiles, ordered by the best rank of their items (it's a "top profile" list in fact).

Here is the SQL request like you can execute it in PHPMyAdmin for example:

SELECT AVG(i.rank) AS rank, p.* FROM profiles AS p LEFT OUTER JOIN items AS i ON p.id = i.profile_id GROUP BY p.id ORDER BY rank DESC;

I'm new to JPA and I can't find some examples about doing a LEFT OUTER JOIN with CriteriaBuilder (if it's the right thing to do).

I would really appreciate if someone would lead me to the right way (I'm not asking someone to do me the job, just having good clues).

Thank you very much! :)

回答1:

This query can be expressed in JPQL as follows:

SELECT p, AVG(i.rank) as rank
FROM Item i RIGHT JOIN i.profile p
GROUP BY p
ORDER BY rank DESC

Note that you can't write arbitrary JOINs in JPA, only JOINs over relationships, therefore you need a RIGHT JOIN here, because your relationship is unidirectional and source of the relationship should be at the left side.

This query could be translated in JPA 2.0 Criteria API in pretty straightforward way, however, the last time I checked it Hibernate's implementation of Criteria API didn't support right joins (and Play Framework uses Hibernate underneath). So, I think you have to use JPQL query in this case.

来源：https://stackoverflow.com/questions/4750371/how-to-make-a-jpa-query-with-left-outer-join

标签

sql

jpa

criteria