EF Core FluentAPI Multiple Field Issue

Question

I have inherited some code which is now causing an issue w. The code looks similar to the following (albeit redacted).

public class ObjectX {
   public Guid Id { get; set; }
   public List<ObjectY> ListOfY { get; set; }
}

public class ObjectY {
   public Guid Id { get; set; }
   public ObjectX MyX { get; set; }
   public ObjectZ MyZ { get; set; }
}

public class ObjectZ
   public Guid ObjectXId { get; set; }
   public Guid ObjectYId { get; set; }
   public ObjectX MyX { get; set; }
   public ObjectY MyY { get; set; }
}

So just to be clear,

• ObjectX contains a collection of ObjectY
• ObjectY contains an instance of ObjectZ and ObjectX
• ObjectZ contains an instance of both ObjectX and ObjectY

ModelBuilder has the following:

modelBuilder.Entity<ObjectZ>
.HasIndex(p => new { p.ObjectXId, p.ObjectYId })
.IsUnique();

indicating that ObjectX and ObjectY are unique as a pair but can appear in different combinations.

The query that is being used is

var something = context.ObjectX
                  .Where(x => x.Id = <somevalue>)
                  .Include(y => y.ListOfY)
                     .ThenInclude(z => z.MyZ)
                  .SingleOrDefault(); 

The issue I'm encountering is that while the ThenInclude function successfully retrieves the first ObjectZ that matches ObjectY.Id, it doesn't take into account ObjectX.Id.

Is there a way to adjust the query, Fluent definitions, or other aspects to ensure that ObjectX is returned with a list of ObjectY where ObjectY.MyZ matches both ObjectXId and ObjectYId?

I acknowledge that the current state of the database design and other related components may not be optimal, but as previously mentioned, I inherited this setup.