JPOX allows control over whether objects found by a fetch (JPQL query) are locked during that transaction so that other transactions can't update them in the meantime. You can use the JPOX extension org.jpox.rdbms.query.useUpdateLock, set to "true", and this will append "FOR UPDATE" on the end of the SELECT. This can be specified as either a JPQL hint (apply to this query only), or as an EMF property (apply to all queries).

You can also specify this for all queries for all PMs using a PMF property org.jpox.rdbms.useUpdateLock.

With a JPQL query running on an RDBMS the query is compiled into SQL. Here we give a few examples of what SQL is generated. You can of course try this for yourself observing the content of the JPOX log.

In JPQL you specify a candidate class and its alias (identifier). In addition you can specify joins with their respective alias. The JPOX implementation of JPQL will preserve these aliases in the generated SQL.

JPQL:
SELECT Object(P) FROM mydomain.Person P INNER JOIN P.bestFriend AS B

SQL:
SELECT P.ID
FROM PERSON P INNER JOIN PERSON B ON B.ID = P.BESTFRIEND_ID

With the JPQL MEMBER OF syntax this is typically converted into an EXISTS query.

JPQL:
SELECT DISTINCT Object(p) FROM mydomain.Person p WHERE :param MEMBER OF p.friends

SQL:
SELECT DISTINCT P.ID FROM PERSON P
WHERE EXISTS (
    SELECT 1 FROM PERSON_FRIENDS P_FRIENDS, PERSON P_FRIENDS_1 
    WHERE P_FRIENDS.PERSON_ID = P.ID
    AND P_FRIENDS_1.GLOBAL_ID = P_FRIENDS.FRIEND_ID 
    AND 101 = P_FRIENDS_1.ID)