How do you map subclass properties to columns in Table per Hierarchy? - entity-framework

Question

I have a TPH situation where I have an abstract base class and 8 derived classes from it by using a discriminator. Two of them share a list of sub classes.
public abstract class StepBase : FullAuditedEntity<Guid>
{
public int Order { get; set; }
public StepType StepType { get; set; }
}
The thing is I have two types which shares a SubClass
public class DestinationVesselStep : StepBase
{
public virtual List<DestinationVessel> VesselsDestination { get; set; }
}
public class LiquidNitrogenStep : StepBase
{
public virtual List<DestinationVessel> DestinationsBoxes { get; set; }
}
private static void ConfigureVesselsStep(ModelBuilder builder)
{
builder.Entity<DestinationVesselStep>(b =>
{
//Properties
b.HasMany(p => p.VesselsDestination).WithOne().HasForeignKey(x => x.StepId);
});
}
private static void ConfigureLiquidNitrogenStep(ModelBuilder builder)
{
builder.Entity<LiquidNitrogenStep>(b =>
{
//Properties
b.HasMany(p => p.DestinationsBoxes).WithOne().HasForeignKey(x => x.StepId);
});
}
But when I request a LiquidNitrogenStep with two or more destinationBoxes I get the following error:
System.InvalidOperationException : Sequence contains more than one element.
it works fine if I only have one destinationBox
I am expecting to get a LiquidNitrogenStep with all its destination boxes, the error do not happnd with DestinationVesselStep

Answer 1

DestinationVessel.StepId can't refer to both a DestinationVesselStep and LiquidNitrogenStep.
So either add separate foreign keys to DestinationVessel, eg LiquidNitrogenStepId, and DestinationVesselStepId, or make the relationships many-to-many, which uses separate linking tables for each relationship, instead of putting foreign keys on the target Entity.
private static void ConfigureVesselsStep(ModelBuilder builder)
{
builder.Entity<DestinationVesselStep>(b =>
{
//Properties
b.HasMany(p => p.VesselsDestination).WithMany( d => d.DestinationSteps);
});
}
private static void ConfigureLiquidNitrogenStep(ModelBuilder builder)
{
builder.Entity<LiquidNitrogenStep>(b =>
{
//Properties
b.HasMany(p => p.DestinationsBoxes).WithMany(d => d.LiquidNitrogenSteps);
});
}