Fluent NHibernate “Could not resolve property”

Question

I have read a lot of the questions about that same error but none since to match my exact problem. I\'m trying to access the property of an object, itself part of a root obj

Answer 1

You have to think of your QueryOver query as (nearly) directly translating into SQL. With this in mind, imagine this SQL query:

select
    Album.*
from
    Album
where
    Album.Name = 'SomeAlbumName' and
    Album.Artist.Name = 'SomeArtistName'

This won't work because you can't access a related table's properties like that in a SQL statement. You need to create a join from Album to Artist and then use a Where clause:

var riAlbum = 
    session.QueryOver<Album>()
               .Where(al => al.Name == albumName)
           .JoinQueryOver(al => al.Artist)
               .Where(ar => ar.Name == artistName)
           .List()
           .FirstOrDefault();

Also, since you're using FirstOrDefault, you may want to consider moving that logic to the database end. Currently, you're pulling back every record matching your criteria and then taking the first one. You could use .Take to limit the query to 1 result:

var riAlbum = 
    session.QueryOver<Album>()
               .Where(al => al.Name == albumName)
           .JoinQueryOver(al => al.Artist)
               .Where(ar => ar.Name == artistName)
           .Take(1)
           .SingleOrDefault<Album>();

Answer 2

Another explanation is that you are missing your mapping of this property or field in a NHibernateClassMapping definition. I came here about why I was getting this error based on the following scenario.

 var query = scheduleRepository.CurrentSession().Query<Schedule>()
                .Where(x => x.ScheduleInfo.StartDate.Date < dateOfRun.Date);

This was giving me a Could Not Resolve Property error for StartDate. This was a head scratcher, since I use this syntax all the time.

My mapping file was the following:

public class ScheduleInfoMapping : NHibernateClassMapping<ScheduleInfo>
    {
        public ScheduleInfoMapping()
        {
            DiscriminateSubClassesOnColumn("Type");
            Map(x => x.Detail).MapAsLongText();
        }
    }

which was missing the StartDate. Changed to:

public class ScheduleInfoMapping : NHibernateClassMapping<ScheduleInfo>
    {
        public ScheduleInfoMapping()
        {
            DiscriminateSubClassesOnColumn("Type");
            Map(x => x.Detail).MapAsLongText();
            Map(x => x.StartDate);
        }
    }

Which resolved the error.