public <ResultType> ResultType calc(String name, Class type, String expr, Field ... fields) throws DBException {
List<String> fieldNames = new ArrayList<String>();
for (Field field : fields) {
fieldNames.add(field.getFieldName());
}
return (ResultType) new ModelQuery(manager).target(new CalcMultiField(name, type, null, expr, fieldNames, map())).one();
}