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What does EntityManager.getSingleResult() return for a COUNT query?

So.. what is the precise runtime type of foo?

Object foo = em.createQuery("SELECT COUNT(t) FROM com.company.Thing t WHERE prop = :param")
       .setParameter("param", value).getSingleResult();
  
4.8.4 Aggregate Functions in the SELECT Clause The result of a query
  
may be the result of an aggregate
  function applied to a path expression.
  
The following aggregate functions can
  be used in the SELECT clause of a
  query: AVG, COUNT, MAX, MIN, SUM.
  
For all aggregate functions except
  COUNT, the path expression that is the
  argument to the aggregate function
  must terminate in a state-field. The
  path expression argument to COUNT may
  terminate in either a state-field or a
  association-field, or the argument to
  COUNT may be an identification
  variable.
  
Arguments to the functions SUM and AVG
  must be numeric. Arguments to the
  functions MAX and MIN must correspond
  to orderable state-field types (i.e.,
  numeric types, string types, character
  types, or date types).
  
The Java type that is contained in the
  result of a query using an aggregate
  function is as follows:
  
COUNT returns Long.
  
MAX, MIN return the type of the state-field to which they are applied.
  
AVG returns Double.
  
SUM returns Long when applied to state-fields of integral types (other
  than BigInteger); Double when applied
  to state-fields of floating point
  types; BigInteger when applied to
  state-fields of type BigInteger; and
  BigDecimal when applied to
  state-fields of type BigDecimal.
  
If SUM, AVG, MAX, or MIN is used, and
  there are no values to which the
  aggregate function can be applied, the
  result of the aggregate function is
  NULL.
  
If COUNT is used, and there are no
  values to which COUNT can be applied,
  the result of the aggregate function
  is 0.
  
The argument to an aggregate function
  may be preceded by the keyword
  DISTINCT to specify that duplicate
  values are to be eliminated before the
  aggregate function is applied.
  
Null values are eliminated before the
  aggregate function is applied,
  regardless of whether the keyword
  DISTINCT is specified.
                When we use native query, then this method returns BigInteger instead of Long. Can anybody explain this behaviour?
– Sumit Desai
                Feb 20, 2014 at 8:12
NB : there's a difference between JQPL and Native query 
Query query = em.createQuery("SELECT COUNT(p) FROM PersonEntity p " );
query.getSingleResult().getClass().getCanonicalName() --> java.lang.Long
Query query = em.createNativeQuery("SELECT COUNT(*) FROM PERSON " );
query.getSingleResult().getClass().getCanonicalName() --> java.math.BigInteger
                I used to do something like Integer.parseInt(q.getSingleResult().toString()); to keep my code "robust", but a cast to Number might be a cleaner solution...
– mmey
                Oct 19, 2016 at 7:16
COUNT(t) specifically returns java.lang.Long. When its appears on its own in this context it is returned as-is. 
(In other contexts the Long generated by COUNT may be wrapped, but not today.)
                second call to query.getSingleResult()   will throw Exception Caused by: org.hibernate.SessionException: Session is closed!. Instead use    	Object obj = query.getSingleResult(); 		if (obj != null) { 			Integer result = Integer.parseInt(obj.toString()); 			return result; 		}  		return Integer.valueOf(0);
– Mohammad Javed
                Jun 16, 2020 at 11:23
  
Second call query.getSingleResult() will throw
  org.hibernate.SessionException: Session is closed!
To avoid the  org.hibernate.SessionException: Session is closed!
 use as below
Object obj = query.getSingleResult();
    if (obj != null) {
        Integer result = Integer.parseInt(obj.toString());
        return result;
    return Integer.valueOf(0);
Count returns long.
Query query = em.createQuery("SELECT COUNT(*) FROM Mandate " );
return (Long) query.getSingleResult();
Mapped your entity with the Query.
                Welcome to SO. Please take a look at the other answers given already. I think, your one doesn't add anything new or improved to them.
– ahuemmer
                Aug 1, 2022 at 7:00
        
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