Select from custom table in QueryDSL

Question

I am using QueryDSL-JPA on JBoss and want at one point select an entity from a different table than the one I am normally using and annotating via @Table. I do not want to create a separate Java class since in the end, it should return me the same class I am using.

Any idea on how to achieve this? Alternatively via the EntityManager or QueryDSL-SQL or Hiberate. Using this approach for accessing historic tables should not be so uncommon...

In FluentJPA this can be easily achieved by derivation. Potentially the same can be done in QueryDSL as well — Konstantin Triger

JRA_TLL JRA_TLL · Accepted Answer · 2019-11-28T06:23:47

The best way I could see was via custom SQL in JPA. QueryDSL does not allow this:

   final AbstractEntityPersister persister = getEntityPersister();
   final String[] idColumnNames = persister.getIdentifierColumnNames();
   Validate.isTrue(idColumnNames.length == 1);

   final String sql = "select * from " + getEntityPersister().getTableName() + HIST_TABLE_SUFFIX + " where " + idColumnNames[0] + " = ?";
   @SuppressWarnings("unchecked")
   final List<E> histList = em.createNativeQuery(sql, getEntityClass()).setParameter(1, id).getResultList();

using

@PersistenceContext(name = "MyDS")
protected EntityManager em;

protected AbstractEntityPersister getEntityPersister() {
    final MetamodelImplementor mm = (MetamodelImplementor) em.getEntityManagerFactory().getMetamodel();
    return (AbstractEntityPersister) mm.entityPersister(getEntityClass());
}

Select from custom table in QueryDSL

1 Answers