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LINQ-to-NHibernate errors when using IQueryable to query component with Select, SelectMany, and OfType

For the purposes of this question, let's say I have a zoo with multiple exhibits. Each exhibit has it's own schedule with a set of activities, as well as a department that is responsible for them and a list of sub-departments.
I have a fairly large LINQ query that I’m using to get any exhibits that has an employee attached to it. When using the query with an IEnumerable (session.Query<Exhibit>().AsEnumerable()) it works fine; however, when I switch the query over to use IQueryable, NHibernate breaks down.
I’ve pinpointed the initial source of the original error to one specific condition in my query:
var filtered = session.Query<Exhibit>().Where(x =>
x.AnimalSchedule.Activities
.OfType<FeedActivity>()
.Any(g => g.ResponsibleDepartment.Manager == employee)
);
Since that condition is pretty long by itself, I went ahead and broke it out step-by-step:
var collection = session.Query<Exhibit>(); // works
var exhibitAnimalSchedules = collection.Select(x => x.AnimalSchedule); // works
var activities = exhibitAnimalSchedules.SelectMany(x => x.Activities); // could not execute query - Incorrect syntax near the keyword 'from'.
var feedActivities = activities.OfType<FeedActivity>(); // Could not find property nor field 'class' in class 'MyProject.Collections.ScheduleActivityCollection'
var filteredFeedActivities = feedActivities.Where(g => g.ResponsibleDepartment.Manager == employee); // Specified method is not supported.
The error on activities also gives the SQL that NHibernate tries to generate:
SELECT
FROM [dbo].[Exhibits] exhibit0_
INNER JOIN [dbo].[ExhibitAnimalSchedules] exhibitanima1_ ON exhibit0_.AnimalScheduleID = exhibitanima1_.ScheduleID
INNER JOIN [dbo].[Schedules] exhibitanima1_1_ ON exhibitanima1_.ScheduleID = exhibitanima1_1_.[ID]
WHERE exhibit0_.ZooID IS NULL
If you notice, NHibernate failed to list out any columns in the SELECT statement.
Am I thinking the wrong way about this query? If this is actually a bug in NHibernate with one of the LINQ lambdas, is there some workaround?
UPDATE - See answer below
It looks like NHibernate is having some trouble figuring out which table to join to for the .SelectMany(x => x.Activities)
For reference, here are all of the simplified Fluent mappings for the classes involved:
public class ExhibitMap : ClassMap<Exhibit>
{
public ExhibitMap()
{
References(p => p.AnimalSchedule).Cascade.All();
}
}
public class ScheduleMap : ClassMap<Schedule>
{
public ScheduleMap()
{
Component(x => x.Activities, m => m {
var cfg = m.HasMany<ScheduleActivity>(Reveal.Member<ScheduleActivityCollection>("_innerList")).LazyLoad();
cfg.KeyColumn("ScheduleID").Inverse();
cfg.ForeignKeyConstraintName("FK_Schedule_Activities");
cfg.Cascade.AllDeleteOrphan();
});
}
}
public class ExhibitAnimalScheduleMap : SubclassMap<ExhibitAnimalSchedule>
{
public ExhibitAnimalScheduleMap()
{
References(x => x.Exhibit).Cascade.None();
}
}
public class ScheduleActivityMap : ClassMap<ScheduleActivity>
{
public ScheduleActivityMap()
{
References(x => x.Schedule).Cascade.None().Not.LazyLoad();
}
}
public class FeedActivityMap : SubclassMap<FeedActivity>
{
public FeedActivityMap()
{
this.References(x => x.ResponsibleDepartment).Cascade.All().Not.LazyLoad();
Component(x => x.Departments, m => m {
var cfg = m.HasMany<FeedActivityDepartment>(Reveal.Member<FeedActivityDepartmentCollection>("_innerList")).LazyLoad();
cfg.KeyColumn("ScheduleID").Inverse();
cfg.ForeignKeyConstraintName("FK_Schedule_Activities");
cfg.Cascade.AllDeleteOrphan();
});
}
}

As #Firo pointed out, NHibernate was having some difficulty with the components I'm using for my custom collections. If you look at the SQL in the question, you'll see that NHibernate failed to join to the Activities table and the Departments table to look for the associated responsible department.
I corrected this by switching over to LINQ query syntax and explicitly joining to the tables. I also avoided issues with the OfType (again, most likely component issues) by checking inline with is and casting with as:
var schedules = from schedule in session.Query<Schedule>()
join activity in session.Query<ScheduleAcivity>() on schedule equals activity.Schedule
join department in session.Query<FeedActivityDepartment>() on activity equals department.FeedActivity
where (activity is FeedActivity && (activity as FeedActivity).ResponsibleDepartment.Manager == employee)
|| (department != null && department.Employee == employee)
select schedule;
var exhibits = from exhibit in session.Query<Exhibit>()
where schedules.Any(x => x == exhibit.AnimalSchedule)
select exhibit;
Note: Sometimes NHibernate is finicky about the names of aliases in the LINQ queries. If you follow this pattern and are still experiencing errors, try changing the names of your aliases (I like to add "temp" in front of them -- from tempSchedule in ..., join tempActivity in ..., etc.).

Linq To Entities Query

Consider the following Query :
var profilelst =
(
from i in dbContext.ProspectProfiles
where i.CreateId == currentUser
select new ProspectProfile
{
ProspectId = i.ProspectId,
Live = i.Live,
Name = i.Name,
ServiceETA = i.Opportunities.OrderByDescending(t => t.FollowUpDate)
.FirstOrDefault()
.ServiceETA.ToString(),
FollowUpDate = i.Opportunities.OrderByDescending(t => t.FollowUpDate)
.FirstOrDefault()
.FollowUpDate
}
)
.ToList();
return profilelst.OrderByDescending(c=>c.FollowUpDate)
.Skip(0).Take(endIndex)
.ToList();
Here in this query please take a look at FollowUpDate and ServiceType, these both i have fetched from Opportunity table, is there any other work around to get these both..
One to Many Relationship in tables is like: ProspectProfile -> Opportunities
Whether the query i have written is ok or is there any another work around that can be done in easier way.

The only thing you can improve is to avoid ordering twice by changing your code to this:
var profilelst
= dbContext.ProspectProfiles
.Where(i => i.CreateId == currentUser)
.Select(i =>
{
var opportunity
= i.Opportunities
.OrderByDescending(t => t.FollowUpDate)
.First();
return new ProspectProfile
{
ProspectId = i.ProspectId,
Live = i.Live,
Name = i.Name,
ServiceETA = opportunity.ServiceETA.ToString(),
FollowUpDate = opportunity.FollowUpDate
}
}).ToList();
return profilelst.OrderByDescending(c => c.FollowUpDate).Take(endIndex).ToList();
I made several changes to your original query:
I changed it to use method chains syntax. It is just so much easier to read in my opinion.
I removed the unnecessary Skip(0).
The biggest change is in the Select part:
I changed FirstOrDefault to First, because you are accessing the properties of the return value anyway. This will throw a descriptive exception if no opportunity exists. That's better than what you had: In your case it would throw a NullReferenceException. That's bad, NullReferenceExceptions always indicate a bug in your program and are not descriptive at all.
I moved the part that selects the opportunity out of the initializer, so we need to do the sorting only once instead of twice.

There are quite a few problems in your query:
You cannot project into an entity (select new ProspectProfile). LINQ to Entities only supports projections into anonymous types (select new) or other types which are not part of your entity data model (select new MySpecialType)
ToString() for a numeric or DateTime type is not supported in LINQ to Entities (ServiceETA.ToString())
FirstOrDefault().ServiceETA (or FollowUpdate) will throw an exception if the Opportunities collection is empty and ServiceETA is a non-nullable value type (such as DateTime) because EF cannot materialize any value into such a variable.
Using .ToList() after your first query will execute the query in the database and load the full result. Your later Take happens in memory on the full list, not in the database. (You effectively load the whole result list from the database into memory and then throw away all objects except the first you have Takeen.
To resolve all four problems you can try the following:
var profilelst = dbContext.ProspectProfiles
.Where(p => p.CreateId == currentUser)
.Select(p => new
{
ProspectId = p.ProspectId,
Live = p.Live,
Name = p.Name,
LastOpportunity = p.Opportunities
.OrderByDescending(o => o.FollowUpDate)
.Select(o => new
{
ServiceETA = o.ServiceETA,
FollowUpDate = o.FollowUpDate
})
.FirstOrDefault()
})
.OrderByDescending(x => x.LastOpportunity.FollowUpDate)
.Skip(startIndex) // can be removed if startIndex is 0
.Take(endIndex)
.ToList();
This will give you a list of anonymous objects. If you need the result in a list of your entity ProspectProfile you must copy the values after this query. Note that LastOpportunity can be null in the result if a ProspectProfile has no Opportunities.

Flattening a loop with lookups into a single linq expression

In Type member support in LINQ-to-Entities? I was attempting to declare a class property to be queried in LINQ which ran into some issues. Here I will lay out the code inside the implementation in hopes of some help for converting it to a query.
I have a class Quiz which contains a collection of Questions, each of which is classified according to a QuestionLevel... I need to determine whether a quiz is "open" or "closed", which is accomplished via an outer join on the question levels and a count of the questions in each level, as compared with a table of maximum values. Here's the code, verbatim:
public partial class Quiz
{
public bool IsClosed
{
get
{
// if quiz has no questions, it's open
if (this.Questions.Count() == 0) return false;
// get a new handle to the EF container to do a query for max values
using (EFContainer db = new EFContainer())
{
// we get a dictionary of LevelName/number
Dictionary<string, int> max = db.Registry
.Where(x => x.Domain == "Quiz")
.ToDictionary(x => x.Key, x => Convert.ToInt32(x.Value));
// count the number of questions in each level, comparing to the maxima
// if any of them are less, the quiz is "open"
foreach (QuestionLevel ql in db.QuestionLevels)
{
if (this.Questions.Where(x => x.Level == ql).Count() < max["Q:Max:" + ql.Name])
return false;
}
}
// the quiz is closed
return true;
}
}
}
so here's my not-yet-working attempt at it:
public static IQueryable<Quiz> WhereIsOpen(this IQueryable<Quiz> query)
{
EFContainer db = new EFContainer();
return from ql in db.QuestionLevels
join q in query on ql equals q.Questions.Select(x => x.Level)
into qs
from q in qs.DefaultIfEmpty()
where q.Questions.Count() < db.Registry
.Where(x => x.Domain == "Quiz")
.Where(x => x.Key == "Q:Max" + ql.Name)
.Select(x => Convert.ToInt32(x.Value))
select q;
}
it fails on account on the join, complaining:
The type of one of the expressions in the join clause is incorrect.
The type inference failed in the call to 'GroupJoin'
I'm still trying to figure that out.
* update I *
ah. silly me.
join q in query on ql equals q.Questions.Select(x => x.Level).Single()
one more roadblock:
The specified LINQ expression contains references to queries that are
associated with different contexts.
this is because of the new container I create for the maximum lookups; so I thought to re-factor like this:
public static IQueryable<Quiz> WhereIsOpen(this IQueryable<Quiz> query)
{
EFContainer db = new EFContainer();
IEnumerable<QuestionLevel> QuestionLevels = db.QuestionLevels.ToList();
Dictionary<string, int> max = db.Registry
.Where(x => x.Domain == "Quiz")
.ToDictionary(x => x.Key, x => Convert.ToInt32(x.Value));
return from ql in QuestionLevels
join q in query on ql equals q.Questions.Select(x => x.Level).Single()
into qs
from q in qs.DefaultIfEmpty()
where q.Questions.Count() < max["Q:Max:" + ql.Name]
select q;
}
but I can't get the expression to compile... it needs me to cast QuestionLevels to an IQueryable (but casting doesn't work, producing runtime exceptions).
* update II *
I found a solution to the casting problem but now I'm back to the "different contexts" exception. grr...
return from ql in QuestionLevels.AsQueryable()
* update (Kirk's suggestion) *
so I now have this, which compiles but generates a run-time exception:
public static IQueryable<Quiz> WhereIsOpen(this IQueryable<Quiz> query)
{
EFContainer db = new EFContainer();
IEnumerable<string> QuestionLevels = db.QuestionLevels.Select(x => x.Name).ToList();
Dictionary<string, int> max = db.Registry
.Where(x => x.Domain == "Quiz")
.ToDictionary(x => x.Key, x => Convert.ToInt32(x.Value));
return from ql in QuestionLevels.AsQueryable()
join q in query on ql equals q.Questions.Select(x => x.Level.Name).Single()
into qs
from q in qs.DefaultIfEmpty()
where q.Questions.Count() < max["Q:Max:" + ql]
select q;
}
which I then call like this:
List<Product> p = db.Quizes.WhereIsOpen().Select(x => x.Component.Product).ToList();
with the resulting exception:
This method supports the LINQ to Entities infrastructure and is not
intended to be used directly from your code.

The issues you're coming across are common when you couple your database objects to your domain objects. It's for this exact reason that it's good to have a separate set of classes that represent your domain and a separate set of classes that represent your database and are used for database CRUD. Overlap in properties is to be expected, but this approach offers more control of your application and decouples your database from your business logic.
The idea that a quiz is closed belongs to your domain (the business logic). Your DAL (data access layer) should be responsible for joining all the necessary tables so that when you return a Quiz, all the information needed to determine whether or not it's closed is available. Your domain/service/business layer should then create the domain object with the IsClosed property properly populated so that in your UI layer (MVC) you can easily access it.
I see that you're access the database context directly, I'd warn against that and encourage you to look into using DI/IoC framework (Ninject is great), however, I'm going to access the database context directly also
Use this class in your views/controllers:
public class QuizDomainObject
{
public int Id {get; set;}
public bool IsClosed {get; set;}
// all other properties
}
Controller:
public class QuizController : Controller
{
public ActionResult View(int id)
{
// using a DI/IoC container is the
// preferred method instead of
// manually creating a service
var quizService = new QuizService();
QuizDomainObject quiz = quizService.GetQuiz(id);
return View(quiz);
}
}
Service/business layer:
public class QuizService
{
public QuizDomainObject GetQuiz(int id)
{
// using a DI/IoC container is the
// preferred method instead of
// access the datacontext directly
using (EFContainer db = new EFContainer())
{
Dictionary<string, int> max = db.Registry
.Where(x => x.Domain == "Quiz")
.ToDictionary(x => x.Key, x => Convert.ToInt32(x.Value));
var quiz = from q in db.Quizes
where q.Id equals id
select new QuizDomainObject()
{
Id = q.Id,
// all other propeties,
// I'm still unclear about the structure of your
// database and how it interlates, you'll need
// to figure out the query correctly here
IsClosed = from q in ....
};
return quiz;
}
}
}

Re: your comment
The join to QuestionLevels is making it think there are two contexts... but really there shouldn't be because the QuestionLevels should contain in-memory objects
I believe that if you join on simple types rather than objects you'll avoid this problem. The following might work for you:
return from ql in QuestionLevels
join q in query
on ql.LevelId equals q.Questions.Select(x => x.Level).Single().LevelId
into qs
(and if this doesn't work then construct some anonymous types and join on the Id)
The problem is that joining on the Level objects causes EF to do some under-the-covers magic - find the objects in the database and perform a join there. If you tell it to join on a simple type then it should send the values to the database for a SELECT, retrieve the objects and stitch them together back in your application layer.

LINQ to SQL find average of field?

I have a ViewModel called EntityRating, one of whose properties is AverageRating.
When I instantiate a new object of my ViewModel (called EntityRating) type, how do I set the EntityRating.AverageRating based on the Rating field (in SQL Server) of the item in question?
I want to do something like this (which obviously doesn't work):
var er = new EntityRating()
{
AverageRating = _db.All<Ratings>(X => X.RatingID = rating.RatingID).Average(RatingField);
};
Can I average the properties of an object in the database and assign it to the property of an object in my code?
(Pretty new, so let me know if any terminology is off, or if you need more info)
Thanks.

LINQ has the .Average extension method, however, that only works on integers. So what you need to do is get an IEnumerable of the RatingField property on all your Rating objects in the database. This can be accomplished by using the .Select extension method of LINQ which Projects each element of a sequence into a new form.
int average = _db.Ratings
.Where(x => x.RatingID == rating.RatingID)
.Select(x => x.RatingField)
.Average();

There's a LINQ function Average() seen here:
http://msdn.microsoft.com/en-us/library/bb399409.aspx
var er = new EntityRating()
{
AverageRating = _db.Where(X => X.RatingID == rating.RatingID)
.Select( x => x.RatingField).Average();
};

Linq to Entities Join -- I don't want anonymous types

I have two tables that are related via a mapping table:
keywords
titles
I am trying to return a list of Map_Keywords_Title (the mapping table's object) based on the results of a join.
Until I added the last part with typedQuery it was just returning objects of anonymous type. I want it to return items of type Map_Keywords_Title so I tried adding the Select at the end (also tried Cast but that failed). The problem now is that the resulting objects are not managed by entity framework so I can't save changes to them.
Is there no straightforward way to do this in Linq to Entities? I'm using VS2008 so I don't yet have the new EF.
public IList<Map_Keywords_Title> MatchingTitleKeywordMappings(string containedInText)
{
var keywords = QueryKeywords();
if (!string.IsNullOrEmpty(containedInText))
{
Expression<Func<Keyword, bool>> exprContainsKeyword = k => containedInText.Contains(k.WordText);
keywords = keywords.Where(exprContainsKeyword);
}
var maps = QueryMap_Keywords_Title();
var anonQuery = keywords.Join(
maps,
key => (int)key.Id,
map => (int)map.Keyword.Id,
(key, map) => new
{
map.Id,
map.Keyword,
map.Title
});
var typedQuery = anonQuery.ToList().Select(anon => new Map_Keywords_Title()
{
Id = anon.Id,
Keyword=anon.Keyword,
Title=anon.Title
});
return typedQuery.ToList();
}

Ok, I got tired of comments...
using( someContext sc = new someContext())
{
sc.Map_Keywords_Title.Include("Title")
.Include("Keyword")
.Where( mkt => containedInText.Contains(mkt.Keyword.WordText));
}
Is that anywhere close to what you want?