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From "Patrick Linskey (JIRA)" <j...@apache.org>
Subject [jira] Commented: (OPENJPA-576) Recursively embedded entities generate an extra and reduntant SQL call to the database.
Date Tue, 22 Apr 2008 06:19:21 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-576?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12591213#action_12591213
] 

Patrick Linskey commented on OPENJPA-576:
-----------------------------------------

>From a conversation with Sandeep:

> We initialize the boolean loaded = true; so we go with the assumption
> that we don't need to reload anything and everything we need is already
> in the result set. The variable gets set to false only if a required
> field is not loaded as per the fetch configuration and then we retry
> 
>        if (!loaded) {
>          em.load(fetch);
>        }
> 
> So the embedded entity remains hollow if some of the fields are not
> present in the result set and they are not present in the fetch
> configuration.


> Recursively embedded entities generate an extra and reduntant SQL call to the database.
> ---------------------------------------------------------------------------------------
>
>                 Key: OPENJPA-576
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-576
>             Project: OpenJPA
>          Issue Type: Bug
>          Components: jdbc
>         Environment: OpenJPA 1.1.0-SNAPSHOT
> version id: openjpa-1.1.0-SNAPSHOT-r422266:647033
> Apache svn revision: 422266:647033
> os.name: Windows XP
> os.version: 5.1
> os.arch: x86
> java.version: 1.6.0_05
> java.vendor: BEA Systems, Inc.
>            Reporter: Sandeep Shrivastava
>             Fix For: 1.1.0
>
>         Attachments: OPENJPA-576.patch
>
>   Original Estimate: 24h
>  Remaining Estimate: 24h
>
> Consider the following persistent class model. The accessor methods are removed for the
sake of brevity.
> public class EmbeddedOwnerPC {
>     private int id1;
>     private int id2;
>     private String stringField;
>     private EmbeddedPC embedded;
>     private ComplexEmbeddedPC complexEmbedded;
> }
> public class EmbeddedPC {
>     private int intField;
>     private String stringField;
> }
> public class ComplexEmbeddedPC  extends RecursivelyEmbeddedPC {
>     private String stringField;
>     private EmbeddedOwnerPC ownerField;
>     private Set stringSet = new HashSet();
> }
> public class RecursivelyEmbeddedPC {
>     private EmbeddedPC embedded;
> }
> When trying to retrieve the EmbeddedOwner entity with a given fetch plan that includes
the complexEmbedded and the embedded fields in the RecursivelyEmbeddedPC class it generate
the following 2 SQL statements to load the entity.
> SELECT t0.TYP, t0.VERSN, t0.EMBEDDED_NULL, t0.ID1, t0.ID2, t0.INTFIELD1, 
> t0.STRINGFIELD3, t0.STRINGFIELD FROM EMBEDDEDOWNERPC t0 WHERE t0.ID1 = ? AND t0.ID2 =
? FOR UPDATE
> SELECT t0.ID1, t0.ID2 FROM EMBEDDEDOWNERPC t0 WHERE t0.ID1 = ? AND t0.ID2 = ? 
> FOR UPDATE
> The second call is reduntant and not needed. The fix is to the EmbedFieldStrategy class
load method to ensure that all fields that are required to be loaded as per the fetch plan
and included from the result set and ONLY when this is not true then generate the extra call
otherwise return a hollow embedded entity. In the above test case the extra call was generated
to get the stringSet field which was not specified in the fetch plan but the call is made
out nevertheless which just selects the primary keys with the same where clause.

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