Retrieving single value using JPA?

Question

Is there any support by JPA to map single values to scalar data types? For example, to map NUM in the following query

SELECT COUNT(*) AS NUM FROM EMPLOYEES

to some variable

int numerOfEmployees

or do I have to use JDBC for such use cases?

score 17 · Accepted Answer · edited Jan 12 '16 at 15:06

17

Yes, you can return scalar types from JPQL queries

long num = ((Number)em.createQuery("select count(e) from Employee e")
                    .getSingleResult()).longValue();

as well as from native SQL queries:

long num = ((Number)em.createNativeQuery("select count(*) from Employees")
                    .getSingleResult()).longValue();

Note that in some cases result type may depend on the database, i.e. it can be something like BigDecimal.

edited Jan 12 '16 at 15:06

eckes

answered Dec 01 '11 at 14:08

axtavt

Doh, thanks. Did not understood that was possible from the docs: http://docs.oracle.com/javaee/6/api/javax/persistence/EntityManager.html#createNativeQuery(java.lang.String) [Note that I had to use an object type and use its intValue() to make your example work.] – Jan Algermissen Dec 01 '11 at 14:23
I updated the solution to use `(Number)...longValue()` which is a super type of `BigInteger`, I am not sure if there is any DB/driver which does not return a subtype of `Number` for this case but the `(long)` cast in the origiinal answer does "never" work for me. (I also wonder if you could specify `Number.class` as a type mapping just to be sure (Double.class seems not to work: http://stackoverflow.com/questions/8959771/jpql-native-query-using-sum-and-count) – eckes Jan 12 '16 at 15:12

1 Answers1