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" );

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

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