Entity Framework Include Record with certain value in a Navigation Property

Question

I am using Entity Framework 6 Code First and I'm configuring the mapping of my domain model with Fluent API. I don't see how to create a navigation properties for a Table which is a little tricky. I have several objects which can make noise, I would like to record that noise in a NoiseRecord Table.

I need some kind of conditional mapping, something like that :

modelBuilder.Entity<NoiseRecord>().HasRequired(n=>n.Origine.OrigineType()=="Car").WithMany(c=>c.NoiseRecords);

That would be the mapping of the Car Navigation Property to avoid that, for example, it includes record related to Planes.

Here is my code

public interface INoisy
{
    int ID {get; set;}
    string OriginType()
    ...
    //And other useful things not related to persistence
}


public class Car : INoisy
{
    ...
    ICollection<NoiseRecord> NoiseRecords { get; set; }
    string OrigineType()
    {
        return "Car";
    }
}

public class Plane : INoisy
{
    ...
    ICollection<NoiseRecord> NoiseRecords {get; set;}
    string OrigineType()
    {
        return "Plane";
    }
}

And a couple of other classes implement INoisy also. Below is the NoiseRecord Table.

public class NoiseRecord
{
    public int RecordID {get; set;}
    public INoisy NoiseOrigine {get; set;}
    public double NoiseMagnitude {get; set;}
}

I'm looking for a way to achieve that with Fluent API.

Thank you !

Answer 1

First of all, it is not possible to use interfaces as navigation properties. But you could use an abstract base class for your noise origins

public abstract class NoiseOrigin
{
    public NoiseOrigin()
    {
        this.NoiseRecords = new Collection<NoiseRecord>();
    }

    public int Id { get; set; }

    public ICollection<NoiseRecord> NoiseRecords { get; set; }
}

public class Car : NoiseOrigin {}

public class Plane : NoiseOrigin { }

public class NoiseRecord
{
    public int Id { get; set; }

    public int OriginId { get; set; }
    public NoiseOrigin Origin { get; set; }

    public double NoiseMagnitude { get; set; }
}

Your fluent API mapping whould look like this

public class NoiseModelContext : DbContext
{
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<Car>().Map(p => p.Requires("Type").HasValue("Car"));
        modelBuilder.Entity<Plane>().Map(p => p.Requires("Type").HasValue("Plane"));
    }

    public DbSet<NoiseOrigin> NoiseOrigins { get; set; }

    public DbSet<NoiseRecord> NoiseRecords { get; set; }
}

To get all car noise records your query will look like

using (var db = new NoiseModelContext()) {
    var records = db.NoiseRecords.Where(p => p.Origin is Car);
    // or like this - the result is the same.
    var records2 = db.NoiseOrigins.OfType<Car>().SelectMany(p => p.NoiseRecords);
}