如何在Nhibernate中进行子查询? [英] How to do subqueries in nhibernate?

问题描述

我需要对子集合进行子查询，但无法正常工作.

I need to do a subquery on a sub collection but I can't get it to work.

我尝试过

 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();

我明白了

不能在条件上使用子查询 没有投影.

Cannot use subqueries on a criteria without a projection.

推荐答案

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，如果您只想要完成的任务，那么...

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>();

或考虑在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.然后您的Task对象将只包含该学生完成的Tasks ...

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

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