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From "Vermeulen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (OPENJPA-134) Extra unneeded SQL joins for OneToMany relationship with fetch type EAGER
Date Tue, 20 Nov 2012 08:44:58 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-134?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13500920#comment-13500920
] 

Vermeulen commented on OPENJPA-134:
-----------------------------------

Unfortunately for the above eager bidirectional Order and Customer example, when selecting
from Order instead of Customer, OpenJPA still uses "load field" for Customer.orders for each
Customer that was fetched. Another problem (very similar, both A and C are Order and B is
Customer) happens when selecting A from A *..1 B 1..* C. OpenJPA loads B's List<C> using
a "load field" for each B. See OPENJPA-2296.
                
> Extra unneeded SQL joins for OneToMany relationship with fetch type EAGER
> -------------------------------------------------------------------------
>
>                 Key: OPENJPA-134
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-134
>             Project: OpenJPA
>          Issue Type: Bug
>          Components: sql
>            Reporter: Catalina Wei
>            Assignee: Fay Wang
>             Fix For: 0.9.7
>
>         Attachments: openjpa134_3.patch
>
>
> Running JPAConfiguration default setting for EagerFetchMode (FetchModeValue.EAGER_PARALLEL),

> the SQL generated is sub-optimal.
> Consider the following entities:
>                                      lineitems( OneToMany ) 
>             Order  <===========================> OrderItem
>                                     order ( ManyToOne )
> Case 1:  why not combining 2 SQL to 1 SQL ?
> =================================================================================================
> Order.lineitmes(EAGER):
> OrderItem.order(LAZY):
> Executing query: select o from Order o
> 2173  demo  TRACE  [main] openjpa.jdbc.SQL - <t 1094730048, conn 1318342292> executing
prepstmnt 1299336562 
> SELECT t0.oid, t0.version, t0.amount, t0.customer_countryCode, t0.customer_id, t0.delivered,
t0.shipaddr FROM Order t0
> 2213  demo  TRACE  [main] openjpa.jdbc.SQL - <t 1094730048, conn 1318342292> [40
ms] spent
> 2223  demo  TRACE  [main] openjpa.jdbc.SQL - <t 1094730048, conn 1318342292> executing
prepstmnt 1406424020 
> SELECT t0.oid, t1.lid, t1.version, t1.cost, t1.order_oid, t1.part_partno, t1.quantity
FROM Order t0 INNER JOIN OrderItem t1 ON t0.oid = t1.order_oid ORDER BY t0.oid ASC
> Case 2: extra unneeded LEFT OUTER JOIN,  if eliminated, the selection aliase t2 should
change to t1:
> =============================================================================================
> Order.lineitmes(EAGER):
> OrderItem.order(LAZY):
> Executing query: select o from Order o left join fetch o.lineitems
> 2403  demo  TRACE  [main] openjpa.jdbc.SQL - <t 1094730048, conn 1314410072> executing
prepstmnt 1500797300 
> SELECT t0.oid, t0.version, t0.amount, t0.customer_countryCode, t0.customer_id, t0.delivered,
t0.shipaddr, t2.order_oid, t2.lid, t2.version, t2.cost, t2.part_partno, t2.quantity FROM Order
t0 LEFT OUTER JOIN OrderItem t1 ON t0.oid = t1.order_oid LEFT OUTER JOIN OrderItem t2 ON t0.oid
= t2.order_oid ORDER BY t2.order_oid ASC
> Case  3: why not generating 1 SQL ?
> ==================================================================================================
> Order.lineitmes(EAGER):
> OrderItem.order(EAGER):
> Executing query: select o from Order o
> 2343  demo  TRACE  [main] openjpa.jdbc.SQL - <t 1094730048, conn 1318342292> executing
prepstmnt 384833264 SELECT t0.oid, t0.version, t0.amount, t0.customer_countryCode, t0.customer_id,
t0.delivered, t0.shipaddr FROM Order t0
> 2383  demo  TRACE  [main] openjpa.jdbc.SQL - <t 1094730048, conn 1318342292> [40
ms] spent
> 2393  demo  TRACE  [main] openjpa.jdbc.SQL - <t 1094730048, conn 1318342292> executing
prepstmnt 1722705582 
> SELECT t0.oid, t1.lid, t1.version, t1.cost, t2.oid, t2.version, t2.amount, t2.customer_countryCode,
t2.customer_id, t2.delivered, t2.shipaddr, t1.part_partno, t1.quantity FROM Order t0 INNER
JOIN OrderItem t1 ON t0.oid = t1.order_oid LEFT OUTER JOIN Order t2 ON t1.order_oid = t2.oid
ORDER BY t0.oid ASC
> 2393  demo  TRACE  [main] openjpa.jdbc.SQL - <t 1094730048, conn 1318342292> [0
ms] spent
> 3134  demo  TRACE  [main] openjpa.jdbc.SQL - <t 1094730048, conn 1318342292> executing
prepstmnt 950548648 
> SELECT t0.lid, t0.version, t0.cost, t1.oid, t1.version, t1.amount, t1.customer_countryCode,
t1.customer_id, t1.delivered, t1.shipaddr, t0.part_partno, t0.quantity FROM OrderItem t0 LEFT
OUTER JOIN Order t1 ON t0.order_oid = t1.oid WHERE t0.order_oid = ? [params=(int) 88]
> 3134  demo  TRACE  [main] openjpa.jdbc.SQL - <t 1094730048, conn 1318342292> [0
ms] spent
> Case 4:  duplicate selections and redundant joins
> ==================================================================================================
> Order.lineitmes(EAGER):
> OrderItem.order(EAGER):
> Executing query: select o from Order o left join fetch o.lineitems
> 2273  demo  TRACE  [main] openjpa.jdbc.SQL - <t 1094730048, conn 1307463150> executing
prepstmnt 1565154634 
> SELECT t0.oid, t0.version, t0.amount, t0.customer_countryCode, t0.customer_id, t0.delivered,
t0.shipaddr, t2.order_oid, t2.lid, t2.version, t2.cost, t3.oid, t3.version, t3.amount, t3.customer_countryCode,
t3.customer_id, t3.delivered, t3.shipaddr, t2.part_partno, t2.quantity FROM Order t0 LEFT
OUTER JOIN OrderItem t1 ON t0.oid = t1.order_oid LEFT OUTER JOIN OrderItem t2 ON t0.oid =
t2.order_oid LEFT OUTER JOIN Order t3 ON t2.order_oid = t3.oid ORDER BY t2.order_oid ASC

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