使用 Entity Framework Core 5，如何嵌套查询并且仍然有 IQueryable？

Question

I have two entities that I want to combine and return just one IQueryable from it. That is, as an example, think of a conference app where I have Speakers and Sessions and Events .

If I do a big join of all three and then I ask for all the sessions associated with one speaker (across all events), I get a return record for every event when in reality I just want one speaker record with all the sessions as detail.

That is, my EF query would look like this:

var q1 = from speaker in db.speakers
         join sessions in db.sessions on speaker.Id equals session.speakerId
         join event in db.sessions on session.EventId equals event.Id
         where speaker.Id = 101

What I want is something like the ability to first, create a speaker query

var q2 = from speaker in db.speakers
         where speaker.Id = 101

Then, create another query that gives me all the speakers sessions over all years

var q3 = join sessions in db.sessions on speaker.Id equals session.speakerId
         join event in db.sessions on session.EventId equals event.Id
         where session.AttendeeId = 101

and finally, I'm really looking for one query, qFinal that combines them.

var qFinal = q2 that has a collection of sessions, or basically, what q3 returns.

Keeping in mind that the Attendee entity contains a collection of sessions.

I realize that my pseudo code above does not really compile but my real problem is much more complex and I thought it easier to explain in simpler terms.

Answer 1

I think here you need Include usage.

var query = db.speakers
  .Include(s => s.sessions.Where(x => x.AttendeeId = 101))
  .Where(s => s.Id = 101);