Table per Hierarchy (TPH) Discriminator Value - entity-framework

Question

We're using the fluent API to map a domain model to an existing database.
The database has a column called Discriminator, but the value stored in the column is not the same as the Type that the row relates to.
Given:
public class Vehicle
{
public int Id { get; set; }
}
public class Car : Vehicle
{
public int Doors { get; set; }
}
public class Bike : Vehicle
{
public bool Stubby { get; set; }
}
Can anyone tell me why this works:
public class VehicleMapping : EntityTypeConfiguration<Vehicle>
{
public VehicleMapping()
{
HasKey(x => x.Id);
Property(x => x.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
Map<Car>(x => x.Requires("Discriminato").HasValue("C"));
Map<Bike>(x => x.Requires("Discriminato").HasValue("B"));
}
}
and this does not (just the requires bit has changed)
public class VehicleMapping : EntityTypeConfiguration<Vehicle>
{
public VehicleMapping()
{
HasKey(x => x.Id);
Property(x => x.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
Map<Car>(x => x.Requires("Discriminator").HasValue("C"));
Map<Bike>(x => x.Requires("Discriminator").HasValue("B"));
}
}
EDIT
Sorry, to clarify what I'm asking:
Why is it not possible to use the default column name, but change the value/type that's stored in that column?
Is it possible?
Is there a workaround if not? (other than changing our schema)

Answer 1

Entity Framework TPH by default uses a column called Discriminator and your second code block is messing with that column. From MSDN:
By default, the discriminator column is added to the table with the
name “Discriminator” and the CLR type name of each type in the
hierarchy is used for the discriminator values. You can modify the
default behavior by using the fluent API.
So if you need to modify it, you need to choose your own name for the column which is what your first code block is doing and calling it Discriminato.