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https://issues.apache.org/jira/browse/OPENJPA-1920?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13493954#comment-13493954
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Vermeulen edited comment on OPENJPA-1920 at 11/9/12 11:54 AM:
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I used the Eclipse debugger which I also used for the related OPENJPA-2296.
When JDBCStoreManager.createEagerSelects considers the TestEntity.strings field
for parallel select, the expression fms[i].supportsSelect(sel,
Select.EAGER_PARALLEL, sm, this, fetch) returns 0 so it is ignored for
efficient eager fetching.
Does this mean that this kind of mapping does not support parallel fetch? Why
not? Is this easy to add? Why doesn't it do join fetch instead?
(EDIT: from the debugger I can see that this fetch mode is also considered
inside JDBCStoreManager.createEagerSelects but somehow also rejected)
was (Author: slowstrider):
I used the Eclipse debugger which I also used for the related OPENJPA-2296.
When JDBCStoreManager.createEagerSelects considers the TestEntity.strings field
for parallel select, the expression fms[i].supportsSelect(sel,
Select.EAGER_PARALLEL, sm, this, fetch) returns 0 so it is ignored for
efficient eager fetching.
Does this mean that this kind of mapping does not support parallel fetch? Why
not? Is this easy to add? Why doesn't it do join fetch instead?
> N+1 select with entities that contain Maps (even with FetchType.EAGER)
> ----------------------------------------------------------------------
>
> Key: OPENJPA-1920
> URL: https://issues.apache.org/jira/browse/OPENJPA-1920
> Project: OpenJPA
> Issue Type: Improvement
> Components: kernel
> Affects Versions: 2.0.0
> Reporter: Vermeulen
>
> When I have an entity that contains a Map, e.g.:
> @Entity
> public class TestEntity {
> @ElementCollection(fetch = FetchType.EAGER)
> Map<String, String> strings = new HashMap<String, String>();
> }
> And I select all existing entities
> String query = "SELECT z FROM " +
> TestEntity.class.getSimpleName()
> + " z";
> List<TestEntity> result = em.createQuery(query,
> TestEntity.class)
> .getResultList();
> n + 1 selects are performed which can be seen by using <property
> name="openjpa.Log" value="DefaultLevel=TRACE" />
> 917 testPU TRACE [main] openjpa.Query - Executing query: SELECT z FROM
> TestEntity z
> 918 testPU TRACE [main] openjpa.jdbc.SQL - <t 4837279, conn 6040101>
> executing prepstmnt 17507279 SELECT t0.id, t0.name FROM TestEntity t0
> 918 testPU TRACE [main] openjpa.jdbc.SQL - <t 4837279, conn 6040101> [0
> ms] spent
> 919 testPU TRACE [main] openjpa.jdbc.SQLDiag - load field: 'strings' for
> oid=entities.TestEntity-1 class entities.TestEntity
> 919 testPU TRACE [main] openjpa.jdbc.SQL - <t 4837279, conn 6040101>
> executing prepstmnt 7493991 SELECT t0.KEY0, t0.value FROM TestEntity_strings
> t0 WHERE t0.TESTENTITY_ID = ? [params=(long) 1]
> 919 testPU TRACE [main] openjpa.jdbc.SQL - <t 4837279, conn 6040101> [0
> ms] spent
> 920 testPU TRACE [main] openjpa.jdbc.SQLDiag - load field: 'strings' for
> oid=entities.TestEntity-51 class entities.TestEntity
> 920 testPU TRACE [main] openjpa.jdbc.SQL - <t 4837279, conn 6040101>
> executing prepstmnt 7200207 SELECT t0.KEY0, t0.value FROM TestEntity_strings
> t0 WHERE t0.TESTENTITY_ID = ? [params=(long) 51]
> etc.....
> It doesn't matter whether or not I use <property
> name="openjpa.jdbc.EagerFetchMode" value="parallel"/> or <property
> name="openjpa.jdbc.EagerFetchMode" value="join"/>.
> This is extremely inefficient when I wish to load a list of products that
> have their name set in multiple languages by using a Map from language to
> String.
> As a workaround I can turn the Map into a List and search the List myself for
> the right entry.
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