EF 4.3.1 Include inherited navigation properties in LinqToEntities query

c#, ef-code-first, entity-framework-4.3, inheritance, navigation-properties

Solution

No, you don't miss anything. Actually you ran into an old Entity Framework bug. Your second query can be written like this:

var result = dataContext.ASet.OfType<AA>().Include("ChildC").ToList();

(when you replace your DbSet `AASet` by `ASet`).

For this type of eager loading of one-to-one mapped children on inherited types this article applies: http://weblogs.asp.net/johnkatsiotis/archive/2010/04/28/huge-ef4-inheritance-bug.aspx

The bug has been reported long time ago here: https://connect.microsoft.com/VisualStudio/feedback/details/544639/ef4-inheritance-defined-using-queryview-doesnt-work-properly-with-association

The bug still exists in EF 4.3.1. But Microsoft has announced in this thread that the bug is fixed in .NET 4.5 ( = EF 5.0).

The code would work if the relationship is one-to-many instead of one-to-one. Lazy or explicit loading would work as well (also with one-to-one relationship), I believe:

var result = dataContext.ASet.OfType<AA>().ToList();
foreach (var item in result)
    dataContext.Entry(item).Reference(a => a.ChildC).Load();

But this will generate multiple queries. If you don't have performance problems with multiple queries I would prefer the last workaround - until you can migrate to EF 5.0.

Problem

I'm trying to setup a simple inheritance scenario with EF 4.3.1 using code first approch and fluent configuration. I've created an abstract base type 'A' with a one-to-one navigation property and an inherited class 'AA' also with a one-to-one navigation property has following : ``` public abstract class A { public Guid ID { get; set; } public B ChildB { get; set; } } public class AA : A { public C ChildC { get; set; } } public class B { public Guid ID { get; set; } public A Parent { get; set; } } public class C { public Guid ID { get; set; } public AA Parent { get; set; } } public class AConfiguration : EntityTypeConfiguration<A> { public AConfiguration() { this.HasRequired(o => o.ChildB) .WithRequiredPrincipal(o => o.Parent); this.Map(o => { o.ToTable("A"); }); } } public class AAConfiguration : EntityTypeConfiguration<AA> { public AAConfiguration() { this.HasRequired(o => o.ChildC) .WithRequiredPrincipal(o => o.Parent); this.Map(o => { o.ToTable("AA"); }); } } public class BConfiguration : EntityTypeConfiguration<B> { public BConfiguration() { this.HasRequired(o => o.Parent) .WithRequiredDependent(o => o.ChildB); this.Map(o => { o.ToTable("B"); }); } } public class CConfiguration : EntityTypeConfiguration<C> { public CConfiguration() { this.HasRequired(o => o.Parent) .WithRequiredDependent(o => o.ChildC); this.Map(o => { o.ToTable("C"); }); } } public class DataContext : DbContext { protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Configurations.Add<A>(new AConfiguration()); modelBuilder.Configurations.Add<AA>(new AAConfiguration()); modelBuilder.Configurations.Add<B>(new BConfiguration()); modelBuilder.Configurations.Add<C>(new CConfiguration()); } public DbSet<AA> AASet { get; set; } public DbSet<B> BSet { get; set; } public DbSet<C> CSet { get; set; } } ``` When I try to get my data back with the first level of navigation property, it works as expected : ``` ... dataContext.AASet.Include("ChildB") ... ``` But when I try to include the navigation property of the inherited type like following : ``` ... dataContext.AASet.Include("ChildC") ... ``` I get an EntityCommandCompilationException at runtime with the following inner exception message : The ResultType of the specified expression is not compatible with the required type. The expression ResultType is 'Transient.reference[...A]' but the required type is 'Transient.reference[...AA]'. Parameter name: arguments[0] Has anybody encountered a similar issue ? I am probably missing something but I can't see what's wrong with this sample. What can I do to get my model works as expected ?

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