如何在nhibernate中进行子查询？

我需要对子集合执行子查询，但无法让它工作。

我试过这个

 Task tAlias = null;
        List<Task> result = session.QueryOver<Task>(() => tAlias)
                                   .Where(Restrictions.In(Projections.Property(() => tAlias.Course.Id), courseIds))
                                   .WithSubquery.WhereExists(QueryOver.Of<CompletedTask>().Where(x => x.Student.StudentId == settings.StudentId))                                     
().ToList();

但我得到

无法对条件使用子查询 没有投影。

session.QueryOver<Task>(() => tAlias)
    .WhereRestrictionsOn(x => x.Course.Id).IsIn(courseIds)
    .WithSubquery.WhereExists(QueryOver.Of<CompletedTask>()
        .Where(x => x.id == tAlias.id) //not sure how you need to link Task to CompletedTask
        .Where(x => x.Student.StudentId == settings.StudentId)
        .Select(x => x.id)) //exists requires some kind of projection (i.e. select clause)
    .List<Task>();

或者，如果您只想完成任务，那么......

Task taskAlias = null;

session.QueryOver<CompletedTask>()
    .JoinAlias(x => x.Task, () => taskAlias)
    .WhereRestrictionsOn(() => taskAlias.Course.Id).IsIn(courseIds)
    .Where(x => x.Student.StudentId == settings.StudentId)
    .List<CompletedTask>();

或者考虑在 Task.CompletedTasks 集合上设置学生过滤器。我以前从未使用过此功能。我相信您必须在运行查询之前启用过滤器并设置学生参数。那么你的任务对象将只包含该学生完成的任务......

http://nhibernate.info/doc/nh/en/index.html#filters http://nhibernate.info/doc/nh/en/index.html#filters