[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-2463) ClassCastException when Hibernate tries to cache results using ResultTransformer

[Tim Leahy (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-2463?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_29520 ] 

Tim Leahy commented on HHH-2463:
--------------------------------

We're also facing this same problem with out projects. Our applications and persistence library were rewritten to use Hibernate by an offshore company however it was not built to scale very well. The database was fully normalized and restructured as part of the rewrite and getting the full object back for queries put too much load on our database, memory, network, and cpu. We eventually decided to start using projections in the existing criteria queries to only get the data we needed.

When we started converting the criteria queries to use projections with a result transformer we discovered we could not cache the queries because of this bug. Manually mapping Object[] to beans after the query is less than ideal, so we ended up using HQL with dynamic bean instantiation and with a set of beans with some pretty big constructors. Every time we find an expensive criteria query we have to completely rewrite it, we'd like to stop doing that.

> ClassCastException when Hibernate tries to cache results using ResultTransformer
> --------------------------------------------------------------------------------
>
>                 Key: HHH-2463
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-2463
>             Project: Hibernate3
>          Issue Type: Bug
>    Affects Versions: 3.2.2
>            Reporter: Peak user
>
> When Hibernate executes a cacheable query using a ResultTransformer, it will attempt to cache the results AFTER applying the ResultTransformer. The problem is that the ResultTransformer may modify the data in a way that Hibernate won't understand it anymore, and in this case it will generate a ClassCastException when trying to cache it.
> This problem could be easily solved if Hibernate cached results before applying the ResultTransformer instead of afterwards.
> Here's a sample code to reproduce this problem:
> class ToMapResultTransformer implements ResultTransformer {
>     private String[] properties;
>     public ToMapResultTransformer(String[] properties) {
>         this.properties = properties;
>     }
>     public List transformList(List collection) {
>         return collection;
>     }
>     public Object transformTuple(Object[] tuple, String[] aliases) {
>         Map<String,Object> result = new HashMap<String,Object>(tuple.length);
>         for (int i=0; i<tuple.length; i++) {
>             result.put((properties != null ? properties[i] : aliases[i]), tuple[i]);
>         }
>         return result;
>     }
> }
> Criteria sqlCriteria = createSqlCriteria(session);
> sqlCriteria.setProjection(projections);
> sqlCriteria.setCacheable(true);
> sqlCriteria.setResultTransformer(new ToMapResultTransformer(properties));
> sqlCriteria.list();
> The code above produces the following exception:
> java.lang.ClassCastException: java.util.HashMap
> 	at org.hibernate.cache.StandardQueryCache.put(StandardQueryCache.java:83)
> 	at org.hibernate.loader.Loader.putResultInQueryCache(Loader.java:2185)
> 	at org.hibernate.loader.Loader.listUsingQueryCache(Loader.java:2129)
> 	at org.hibernate.loader.Loader.list(Loader.java:2087)
> 	at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:94)
> 	at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1569)
> 	at org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:283)

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