How to map key properties to differing column types on inherited entities in EF CodeFirst?

Question

I'm trying to implement a TPC inheritance model in EF 4.3 CodeFirst for an existing Oracle database (over which I have no control). I have several sub-types that each map to its own table. Unfortunately, some of the key columns are of datatype number(18,0) instead of integer. EF seems to hate me now.

Here's my base class:

public abstract class Vehicle
{
    public virtual int Id { get; set;}
    public virtual string Color { get; set; }
    //more properties
}

Here are some example sub-types:

public class Car : Vehicle
{        
    //more properties
}

public class Truck : Vehicle
{
    //more properties
}

public class Motorcycle : Vehicle
{
    //more properties
}

And here's my DbContet:

public class VehicleDataContext : DbContext
{
    public DbSet<Vehicle> Vehicles { get; set; }
    public DbSet<Car> Cars { get; set; }
    public DbSet<Truck> Trucks { get; set; }
    public DbSet<Motorcycle> Motorcycles { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Vehicle>().HasKey(x => x.Id);

        modelBuilder.Entity<Car>().Map(m => m.MapInheritedProperties());
        modelBuilder.Entity<Car>().Property(x => x.Id).HasColumnType("decimal");

        modelBuilder.Entity<Truck>().Map(m => m.MapInheritedProperties());
        modelBuilder.Entity<Truck>().Property(x => x.Id).HasColumnType("int");

        modelBuilder.Entity<Motorcycle>().Map(m => m.MapInheritedProperties());
        modelBuilder.Entity<Motorcycle>().Property(x => x.Id).HasColumnType("decimal");

        base.OnModelCreating(modelBuilder);
    }
}

So, I already know to MapInheritedProperties so that all the properties of the base and sub-type are mapped to one table. I'm assuming that I have to tell the base that it HasKey so that EF doesn't complain that my DbSet<Vehicle> doesn't have a key mapped. I'd like to be able to assume that I can "tell" each entity how to map its own key's column type like I've done above. But I think that's not quite it.

Here's a test that fails:

[TestFixture]
public class when_retrieving_all_vehicles
{
    [Test]
    public void it_should_return_a_list_of_vehicles_regardless_of_type()
    {
        var dc = new VehicleDataContext();
        var vehicles = dc.Vehicles.ToList(); //throws exception here
        Assert.Greater(vehicles.Count, 0);
    }
}

The exception thrown is:

The conceptual side property 'Id' has already been mapped to a storage property with type 'decimal'. If the conceptual side property is mapped to multiple properties in the storage model, make sure that all the properties in the storage model have the same type.

As mentioned above, I have no control over the database and it's types. It's silly that the key types are mixed, but "it is what it is".

How can I get around this?

Answer 1

You cannot achieve it through mapping. This is limitation of EF code first. You can map each property (including the key) in inheritance structure only once. Because of that you can have it either integer or decimal in all entities in the inheritance tree but you cannot mix it.

Btw. what happens if you try to use int or decimal for the whole inheritance tree? Does it fail for loading or persisting entity? If not you can simply use the one (probably decimal if it can use whole its range) for all entities.