Count.java

	/**
	 * @return The number of rows matching the given expression.
	 */
	public static long count( ObjectContext oc, Class<? extends DataObject> entityClass, Expression expression ) {
		StringBuilder b = new StringBuilder();
		b.append( "SELECT count(a) " );
		b.append( " FROM " );
		b.append( oc.getEntityResolver().getObjEntity( entityClass ).getName() );
		b.append( " a" );

		List<Object> parameters = new ArrayList<>();

		if( expression != null ) {
			b.append( " WHERE " );
			b.append( expression.toEJBQL( parameters, "a" ) );
		}

		String queryString = b.toString();
		EJBQLQuery query = new EJBQLQuery( queryString );

		for( int i = 0; i < parameters.size(); i++ ) {
			query.setParameter( i + 1, parameters.get( i ) );
		}

		List result = oc.performQuery( query );

		for( Object object : result ) {
			return (Long)object;
		}

		throw new IllegalStateException( "Execution should never reach here (count is returned in the above loop)" );
	}