NHibernate QueryOver

问题

I've searched around but not found what I am doing wrong here.

I have object C which holds a list of object L, object C also holds a reference to class R.

From object L I want to find object R.

I'm trying to do this but I only get null using this code:

L is already an instanced object a function receives.

var t = SessionController.CurrentSession.QueryOver<C>()
  .Where(c => c.Id == L.C_Id)
  .JoinQueryOver<R>(c => c.R)
  .Select(c => c.R).SingleOrDefault();

Any idea what I'm doing wrong here would be appreciated. Thanks

回答1:

The problem is your SingleOrDefault call is returning an instance of class C and I'm guessing there is not instance of class C that has the Id of the associated class R. You'll want to modify your query as follows:

var t = SessionController.CurrentSession.QueryOver<C>()
  .Where(c => c.Id == L.C_Id)
  .JoinQueryOver<R>(c => c.R)
  .Select(c => c.R).SingleOrDefault<R>();

Note the explicit typing of the SingleOrDefault call.

来源：https://stackoverflow.com/questions/6610531/nhibernate-queryover