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From "Vermeulen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (OPENJPA-1920) N+1 select with entities that contain Maps (even with FetchType.EAGER)
Date Fri, 09 Nov 2012 11:54:13 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-1920?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13493954#comment-13493954
] 

Vermeulen commented on OPENJPA-1920:
------------------------------------

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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