Wouter van der Kamp created OPENJPA-2680:
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Summary: entityManager.merge() sends unnecessary select statements
to the database
Key: OPENJPA-2680
URL: https://issues.apache.org/jira/browse/OPENJPA-2680
Project: OpenJPA
Issue Type: Bug
Affects Versions: 2.4.1
Reporter: Wouter van der Kamp
See uploaded test code.
Test.test1() does a merge() on a new object with a @GeneratedValue id. Here
OpenJPA sends this query to the database:
SELECT t0.name FROM Country t0 WHERE t0.id = ? [params=(long) 0]
Presumably to check whether the entity is already present in the database, but
this is unnecessary because it's a new object without an id (id == null).
Workaround for this bug is to use persist() in stead of merge(). But this is
not always possible, for example when using an object which is not known by the
EntityManager. This is Test.test2(), where OpenJPA sends the queries:
SELECT t1.id, t1.name, t0.name FROM Citizen t0 LEFT OUTER JOIN Country t1 ON
t0.countryId = t1.id WHERE t0.id = ? [params=(long) 0]
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