So I have a pair of related objects that are being tied through a secondary key that don’t have the same type and I am trying to relate the objects together. In essence I have something like.

public class A 
{
  Guid PK {get;set;}

  string ReferenceKey {get;set;} // is an internal and external key so generically typed
  
  ICollection<B> RelatedClassBObjs {get;set;} // this can be null

}

public class B 
{
  int Key {get;set}

  A RelatedClassAObj {get;set;}
}

Class A’s ReferenceKey is sometimes a reference to Class B’s Key and so is an int, but in other times it can be an external reference and so could be anything from a GUID to a random string.

I’m attempting to relate the 2 classes using Fluent API doing something like

modelBuilder.Entity<B>(entity=>{
  ... //Property set up omitted 
  entity.HasOne(e => e.RelatedClassAObj)
   .WithMany(d=>d.RelatedClassBObjs)
   .HasForeignKey(e=>e.Key)
   .HasPrincipalKey(d => d.ReferenceKey);
});

and I have the alternate key set up for Class A as well

modelBuilder.Entity<A>(entity=>{
  entity.HasKey(e => e.PK)
    .HasName("PRIMARY");
  entity.HasAlternateKey(e => e.ReferenceKey )
    .HasName("reference_key");
  ... // extra setup omitted 
});

With this setup the join SQL generated looks like

JOIN B b ON b.Key = a.ReferenceKey 

However this seems to be attempting to cast/read the string ReferenceKey as an integer and then blows up when there is a non-integer present. In the SQL this seems to be able to be fixed by adding a cast to string around the b.Key

JOIN B b ON CAST(b.Key as string) = a.ReferenceKey 

But I cannot figure out a way to get fluent API to do this. I have no control over the Data bases, nor over the Linq queries (the model is being used by HotChocolate so I do not have direct Linq/SQL control). Any help would be greatly appreciated.