Problem with foreign key in Entity Framework one to many

I am having some foreign key problems, it turns out that I am doing a revision to an old system in which a new table is added, and in doing so, the following arises.

In short, I have the following 3 classes.

public class StepUp
{
    [Key]
    [Column(Order = 0)]    
    public string CodigoDelfos { get; set; }    
    [Key]
    [Column(Order = 1)]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int Revision { get; set; }
    public virtual ICollection<Accesorio_x_Trafos> Accesorios { get; set; }
    //More irrelevant properties..
}

public class Transformador 
{
    [Key]
    [Column(Order = 0)]
    public string Codigo_delfos { get; set; }
    [Key]
    [Column(Order = 1)]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int Revision { get; set; }
    public virtual ICollection<Accesorio_x_Trafos> Accesorio_x_Trafos { get; set; }
    //More irrelevant properties..
}

public class Accesorio_x_Trafos
{
    [Key]
    [Column(Order = 0)]
    public string CodigoAccesorio { get; set; }        
    [Key]
    [Column(Order = 1)]
    public string CodigoDelfos { get; set; }
    [Key]
    [Column(Order = 2)]
    public int Revision { get; set; }       
    public int? Cantidad { get; set; }    
}

The issue is that both StepUp and Transformador have a 1- * relationship with Accessorio_x_Trafos.

When migrating, the database is created correctly (FKs are added)

(Ignore the FK Accesorios which is one of the properties that I removed so as not to have so much code)

The issue is that when I try, both modify an object of type Transformer (I do it as follows)

//Get any object..
var transformador = mContext.Transformador.First();
//Add random data..
transformador.Accesorio_x_Trafos = new List<Accesorio_x_Trafos>
{
    new Accesorio_x_Trafos 
        { CodigoDelfos = transformador.Codigo_delfos, Revision = transformador.Revision, Cantidad = 1, CodigoAccesorio = "05-CBPA0150000802000P0800"},
    new Accesorio_x_Trafos
        { CodigoDelfos = transformador.Codigo_delfos, Revision = transformador.Revision, Cantidad = 2, CodigoAccesorio = "05-CBPA0150000803150P0700"},
    new Accesorio_x_Trafos
        { CodigoDelfos = transformador.Codigo_delfos, Revision = transformador.Revision, Cantidad = 3, CodigoAccesorio = "05-CBPA0150000803150P0700"}
};
//Save it
mContext.SaveChanges();

But this throws the follow exception

An error occurred while saving entities that do not expose foreign key properties for their relationships. The EntityEntries property will return null because a single entity cannot be identified as the source of the exception. Handling of exceptions while…

And in the InnerException the

Instrucción INSERT en conflicto con la restricción FOREIGN KEY “FK_dbo.Accesorio_x_Trafos_dbo.StepUps_CodigoDelfos_Revision”. El conflicto ha aparecido en la base de datos “DBTrafos”, tabla “dbo.StepUps”.rnSe terminó la instrucción.

How can i deal with this?

Answer

I solve my issue by creating an abstract class that replaced Accessory_x_Trafos in such a way, that you then specify each inherited class with its foreign key and corresponding navigation property.

public abstract class AccesorioTransformador
{
    public Guid Id { get; set; }
    public string CodigoAccesorio { get; set; }
    public int Cantidad { get; set; }   
}

public class AccesorioStepUp : AccesorioTransformador
{
    public string CodigoDelfos { get; set; }
    public int Revision { get; set; }   
    [ForeignKey(nameof(CodigoDelfos)+","+nameof(Revision))]   
    public StepUp.StepUp Transformador { get; set; }
}

public class AccesorioDistribucion : AccesorioTransformador
{
    public string CodigoDelfos { get; set; }
    public int Revision { get; set; }           
    [ForeignKey(nameof(CodigoDelfos) + "," + nameof(Revision))]
    public Transformador Transformador { get; set; }
}

In this way, in each of the corresponding classes, I used properties, either type ICollection<AccesorioStepUp> or type ICollection<AccesorioDistribucion>.