use of entityManager.createNativeQuery(query,foo.class)

by

What you do is called a projection. That’s when you return only a scalar value that belongs to one entity. You can do this with JPA. See scalar value.

I think in this case, omitting the entity type altogether is possible:

   Query query = em.createNativeQuery(  "select id from users where username = ?");  
   query.setParameter(1, "lt");  
   BigDecimal val = (BigDecimal) query.getSingleResult();

Example taken from here.

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