Nhibernate empty query

Question

I have next code

if (user != null)
  query = query.Where(item => item.User.Id == user.Id);
else if (equipment != null)
  query = query.Where(item => false);// TODO: Add logic for equipment

but NHibernate can't build expression tree for item => false. Someday this expression will change, but now it must return empty query. Is there some method to solve this problem?

@stuartd , no. same exception. "Could not determine member type from Constant, False, System.Linq.Expressions.ConstantExpression" — Maksym
– Maksym, Commented May 8, 2013 at 15:05

CountZero · Accepted Answer · 2013-05-08 21:28:38Z

1

Assuming it is an IQueryable of User, try this.

if (user != null)
  query = query.Where(item => item.User.Id == user.Id);
else if (equipment != null)
  query = new List<User>().AsQueryable();

Edit:

OP said it is a IQueryOver not an IQueryiable, had a look at source and QueryOver is protected so can't see how to create an empty one easily right now. My suggestion is to use the LINQ provider if you can so my original answer will work. If it's not possible then this UGLY hack will work for now.

if (user != null)
                query = query.Where(item => item.User.Id == user.Id);
            else if (equipment != null)
                query = query.Where(item => item.User.Id < 0 && item.User.Id > 1);

edited May 8, 2013 at 21:28

answered May 8, 2013 at 15:59

CountZero

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3 Comments

Maksym Over a year ago

AsQueryable() returns IQueryable object, but query is IQueryOver =(

CountZero Over a year ago

Assumption is the mother of all mistakes. Is there a reason you're not using nHibernate's LINQ provider? Generally much nicer if not as powerful. There may be a nicer way but for now you can do this. if (user != null) query = query.Where(item => item.User.Id == user.Id); else if (equipment != null) query = query.Where(item => item.User.Id < 0 && item.User.Id > 1);

Maksym Over a year ago

Thanks! Id is Guid, so I use next expression: query = query.Where(item => item.Id == Guid.Empty);

rivarolle · Accepted Answer · 2013-05-08 21:21:59Z

0

I think I've used

  Where(item => 1 == 0)

answered May 8, 2013 at 21:21

rivarolle

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1 Comment

Maksym Over a year ago

Same exception. "Could not determine member type from Constant, False, System.Linq.Expressions.ConstantExpression". Probably, NHibernate calculates expressions with constants, so we get ours Where(item=>false);

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