Hibernate – How to select an object’s class in HIbernate HQL

hibernatehql

how can I select an object's class in HQL? When I do the following:

select e.class, e.name from Entity e

Hibernate returns an Integer (e.g. [12, "name"]) instead of a class object. How can I return a Java class, or at least the class or entity name? Or, if this is not possible, how can I convert the 12 to a Java class?

For performance reasons, I can't query the full objects, i.e. I can't do

select e from Entity

Regards,
Jochen

Best Answer

if you are hibernate4, you can use HQL function 'type()' to get entity type

select type(e), e.name from Entity e

If you are hibernate3, the session.iterate() return entity as HibernateProxy with id only, and you can get entity name & id from it without initializing.

Iterator iterator = session.createQuery("from Entity e").iterate();
while(iterator.hasNext()) {
    HibernateProxy object = (HibernateProxy)iterator.next();
    System.out.println(object.getHibernateLazyInitializer().getIdentifier());
    System.out.println(object.getHibernateLazyInitializer().getEntityName());
}

Related Solutions

Java – JPA and Hibernate – Criteria vs. JPQL or HQL

I mostly prefer Criteria Queries for dynamic queries. For example it is much easier to add some ordering dynamically or leave some parts (e.g. restrictions) out depending on some parameter.

On the other hand I'm using HQL for static and complex queries, because it's much easier to understand/read HQL. Also, HQL is a bit more powerful, I think, e.g. for different join types.

Java – Hibernate: Parse/Translate HQL FROM part to get pairs class alias, class name

Hardly a good way of doing it, but it seems you can get the AST through some internal interfaces and traverse this:

QueryTranslator[] translators = hqlPlan.getTranslators();
AST ast = (AST)((QueryTranslatorImpl)translators[0]).getSqlAST();
    new NodeTraverser(new NodeTraverser.VisitationStrategy() {
    public void visit(AST node) {
        if(node.getType() == SqlTokenTypes.FROM_FRAGMENT || node.getType() == SqlTokenTypes.JOIN_FRAGMENT) {
            FromElement id = (FromElement)node;
            System.out.println(node+": "+id.getClassAlias()+" - "+id.getClassName());
        }
    }
}).traverseDepthFirst(ast);

So this seems to retrieve the alias-mappings from the compiled query, but I would be very careful using this solution: it typecasts objects to subclasses not usually visible to a hibernate-client and interprets the AST based on guessing the semantics of the different nodes. This might not work on all HQL-statements, and might not work, or have different behaviour, on a future hibernate-version.

Best Answer

Related Solutions

Java – JPA and Hibernate – Criteria vs. JPQL or HQL

Java – Hibernate: Parse/Translate HQL FROM part to get pairs class alias, class name

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