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From "Andrus Adamchik (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CAY-1398) ClassCastException on meaningful FK with non-standard Java to JDBC type mapping
Date Tue, 02 Mar 2010 23:08:27 GMT

    [ https://issues.apache.org/jira/browse/CAY-1398?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12840376#action_12840376
] 

Andrus Adamchik commented on CAY-1398:
--------------------------------------

Wonder if we should force predictable (JDK-independent) iteration order of properties on the
class descriptors. This should have no per-query performance impact (as descriptors are "compiled"
once), and will ensure some consistency. 

> ClassCastException on meaningful FK with non-standard Java to JDBC type mapping
> -------------------------------------------------------------------------------
>
>                 Key: CAY-1398
>                 URL: https://issues.apache.org/jira/browse/CAY-1398
>             Project: Cayenne
>          Issue Type: Bug
>          Components: Core Library
>    Affects Versions: 3.0RC2
>            Reporter: Andrus Adamchik
>            Assignee: Andrus Adamchik
>            Priority: Minor
>             Fix For: Short term future
>
>
> A rather odd case, that nevertheless we should handle:
> TABLE1 (PK INT, FK CHAR(1))
> TABLE2 (PK CHAR(1));
> Class1 (fk : java.lang.Character, class2: Class2)
> I.e. a relationship is mapped with FK also being a meaningful attribute, and attribute
type is not a standard JDBC mapping of CHAR(1) column. Depending on the Class1 entity property
iteration order, SelectTranslator builds a result column either from an "fk" attribute definition
(then it is correctly mapped as java.lang.Character) or from "class2" relationship definition
(which will end up ignoring ObjAttribute and using java.lang.String). Later on when a property
is read from an object, the later case results in ClassCastException (of java.lang.String
into java.lang.Character).
> This is almost impossible to test. For the entity in my project, switching between JDK
1.5 and 1.6 makes all the difference (it fails under 1.5, but this is really random, dependent
on the relationship and attribute relative string key names). 
> A quick (and incorrect) fix is to make SelectTranslator.appendQueryColumns(..) ->
"visitRelationship" check for existence of ObjAttribute for the join DbAttribute to ensure
the right type is used. Although this may result in invalid to-one fault ObjectIds, as the
target entity may not have meaningful ID columns, and the ObjectId derived from FK will not
match ObjectId of the target object fetched directly.
> A correct, but significantly deeper fix is to read the same ResultSet column twice, and
put 2 copies in the DataRow: one for meaningful attribute, and one for generic FK. maybe all
"attributeOverrides" in SelectTranslator should follow this approach (and also other places
where we duplicate the same column in the ResultSet for consistency reasons)

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