问题
I need to do a subquery on a sub collection but I can't get it to work.
I tried this
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();
Yet I get
Cannot use subqueries on a criteria without a projection.
回答1:
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>();
or if you only want the completedtask then just...
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>();
or look into setting up a student filter on the Task.CompletedTasks collection. I've never used this feature before. I believe you have to enable the filter and set the student parameter before you run the query. Then your Task object would only contain completedTasks by that student...
http://nhibernate.info/doc/nh/en/index.html#filters
来源:https://stackoverflow.com/questions/5969250/how-to-do-subqueries-in-nhibernate