Table-per-Hierarchy and Many to Many relationship - entity-framework

Question

this may seem very easy to solve, but the complication I'm having is that I have a table per hierarchy to store all of the entities and I'm not able to create the relationships over the same table. Here is what I have in the DB and classes:
I have just one table named BaseObject with an ID, name and type. I will create two classes for those entities stored in there. Master and Component. The type column is the discriminator. I have another table to store the relationships between both: A master can have many components and a component also can have many other components.
This is the code I have for the classes:
public partial class BaseObject
{
public BaseObject()
{
}
public System.Guid ID { get; set; }
public string Name { get; set; }
public Nullable<int> Type { get; set; }
}
public class MasterObject : BaseObject
{
public virtual ICollection<ComponentObject> Components { get; set; }
public MasterObject()
{
this.Components = new List<ComponentObject>();
}
}
public class ComponentObject : BaseObject
{
public virtual ICollection<MasterObject> MasterObjects { get; set; }
public ComponentObject()
{
this.MasterObjects = new List<MasterObject>();
}
}
And these are the mappings:
public class BaseObjectMap : EntityTypeConfiguration<BaseObject>
{
public BaseObjectMap()
{
// Primary Key
this.HasKey(t => t.ID);
// Table & Column Mappings
this.ToTable("BaseObject");
this.Property(t => t.ID).HasColumnName("ID");
this.Property(t => t.Name).HasColumnName("Name");
//configure the inheritance in here
this.Map<MasterObject>(m => m.Requires("Type").HasValue(1));
this.Map<ComponentObject>(m => m.Requires("Type").HasValue(2));
}
}
public class MasterObjectMap : EntityTypeConfiguration<MasterObject>
{
public MasterObjectMap()
{
this.HasMany<ComponentObject>(t => t.Components)
.WithMany(t => t.MasterObjects)
.Map(c =>
{
c.ToTable("ObjectComponents");
c.MapLeftKey("ComponentObjectID");
c.MapRightKey("BaseObjectID");
});
}
}
public class ComponentObjectMap : EntityTypeConfiguration<ComponentObject>
{
public ComponentObjectMap()
{
this.HasMany<MasterObject>(t => t.MasterObjects)
.WithMany(t => t.Components)
.Map(m =>
{
m.ToTable("ObjectComponents");
m.MapLeftKey("BaseObjectID");
m.MapRightKey("ComponentObjectID");
});
}
}
The thing is that when quering the DB, I can get a Master by accessing the DBSet Masters, but the Component collection always gives a non-sense exception saying that "Problem in mapping fragments starting at line 6:Condition member 'BaseObject.Type' with a condition other than 'IsNull=False' is mapped. Either remove the condition on BaseObject.Type or remove it from the mapping."
I don't understand what's happening. Of course if the classes where pointing each to a table, this would be very easy, but I suspect that is the root of my problem.
Also, I'm just starting with EF. I wanted to create the classes based on my existing DB that I wouldn't like to modify at all. Unless it's really needed. Please guide me if what I'm trying to do is right or wrong, or what should I do first to fully implement EF on this project that is currently using NHibernate.
Any help here? Thanks

Answer 1

Finally I found the issue thanks to this answer: EF4.1 Exception creating Database with table-per-hierarchy inheritance
The problem is in the mapping of the Base class. When using a base class and a discriminator to get the children classes, the discriminator MUST NOT BE a property in neither instance. Just removed the discriminator as property and it worked fine. In my example, column 'Type' is the discriminator.
Hope this helps to someone else.