hql查询可获取以父表ID为键，子对象列表为值的地图

Question

There are two tables parent and child with foreign key relation. Now my requirement is to write hql which return a map with key as parent table id and value as the list of child objects.

Answer 1

OK. You seem to be completely lost, so here's how I would do it:

String hql = 
    "select distinct p from Parent p" // get all the parents
    + " left join fetch p.children";  // with their children
List<Parent> parents = session.createQuery(hql).list();

// now transform this list of parents into a Map
Map<Long, List<Child>> result = new HashMap<Long, List<Child>>(parents.size());
for (Parent parent : parents) {
    result.put(parent.getId(), parent.getChildren());
}

Note that I don't really see the point of this map. If you have the list of parents, each containing its children, the map shouldn't be necessary.