Answer 1

没有使用HQL，我能想到的最优雅的解决方案是使用Criteria对象。以下内容将为您提供您所需要的并且开销非常低：

ICriteria criteria = this._sessionManager.GetCurrentSession().CreateCriteria(typeof(ServiceProvider), "sp");

//set projections for the field and aggregate, making sure to group by the appropriate value
criteria.CreateAlias("sp.ServicesProvided", "s", JoinType.LeftOuterJoin)
   .SetProjection(Projections.ProjectionList()
      .Add(Projections.Property("s.ID"), "serviceID")
      .Add(Projections.Count("sp.ID"), "count")
      .Add(Projections.GroupProperty("s.ID")));

IList<object[]> results = criteria.List();

foreach (object[] entry in results)
{
   int id = (int)entry[0], qty = (int)entry[1];

   //Do stuff with the values
}